A POPULAR TREATISE 
 
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A POPULAR TREATISE 
 
 PH OTOGRAPHY 
 
 A DESCRIPTION OF, AND REMARKS ON, THE 
 
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 D. VAN MONCKHOYEN. 
 
 TRANSLATED BY W. H. THORNTHWAITE, PH.D., F.G.S. 
 
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 LONDON: 
 YIETUE BROTHERS & CO., 1, AMEN CORNER, 
 
 PATERNOSTER ROW. 
 1863. 
 
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PREFACE. 
 
 THE high repute of D. Yan Monckhoven on the 
 Continent as a practical photographer, and the very 
 favourable reviews which his works have from 
 time to time received from the leading photographic 
 journals in this country, have led to the following 
 free translation of his " Traite Populaire de Photo- 
 graphy sur Collodion." The alterations and emen- 
 dations which have been made in the original text, 
 it is hoped, will render the whole more immediately 
 available to the English reader, and acceptable as a 
 handbook of photographic art. 
 
 W. H. THORNTHWAITE. 
 April, 1863. 
 
CONTENTS. 
 
 Chapter Page 
 
 Introductory 1 
 
 I. The plan followed in this work 6 
 
 II. On the preparation of substances required in the manu- 
 facture of photographic collodion . . . .11 
 
 III. Preparation of photographic collodion .... 20 
 
 IV. Cleaning glass plates, &c 25 
 
 V. On the dark room, and photographic laboratory . .28 
 
 VI. Coating with collodion and sensitising the plate . . 30 
 VII. Photographic cameras, lenses, &c. .... 36 
 VIII. On the glass room in which the sitter is placed, and the 
 
 rules to be observed in taking portraits and landscapes 48 
 IX. Development of the latent image obtained in the camera- 
 
 obscnra 55 
 
 X. Fixing and strengthening the negative image . . 64 
 XI. Varnishing the picture . . . . . .67 
 
 XII. The dry collodion, collodio-albumen, and tannin processes 7 1 
 
 XIII. Positive collodion process 84 
 
 XIV. The stereoscope 89 
 
 XV. Printing positive proofs 98 
 
 NOTES. 
 
 Appearance of negatives 121 
 
 Distillation of ether 121 
 
 Preparation of pyroxyiine 122 
 
 Employment of the iodides and bromides . . .122 
 
 Nitrate of silver stains 123 
 
 Preparation of the nitrate of silver bath . . . 124 
 
 Preparation of pyrogallic acid 124 
 
 Photographic optics 125 
 
 Spots on the collodion film . . . . . .130 
 
 Crystallisable acetic acid 131 
 
A GLANCE 
 
 AT THE 
 
 PEINCIPAL PHOTOGRAPHIC PEOCESSES 
 
 NOW IN USE. 
 
 INTRODUCTORY. 
 
 AMONGST the various methods which have been from time 
 to time proposed for the production of pictures by the 
 chemical agency of light, and comprehended under the 
 general term Photography, there are only four the 
 DAGUERREOTYPE, CALOTYPE, ALBUMEN, and COLLODION 
 processes which have been to any extent practically 
 successful. 
 
 The photographic piature is obtained in the 
 
 Daguerreotype process, on polished metal plates ; 
 Calotype, on paper ; 
 
 Albumen, on a film of albumen on glass ; 
 Collodion, on a film of collodion on glass. 
 
 And it is an interesting fact that, although at first sight 
 these processes do not appear to have any connection with 
 each other, there nevertheless does exist one general 
 principle of action, which will be obvious, even to the 
 superficial observer. 
 
 THE DAGUERREOTYPE. This process was. discovered by 
 Niepce and Daguerre. A silver, or silvered copper, plate, 
 highly polished, is placed in the dark on a china dish, con- 
 taining iodine. The vapour of this substance combines 
 with the silver of the metallic plate in such a manner as 
 to produce iodide of silver, a substance sensitive to light. 
 In fact, it is sufficient to expose it behind a perforated card 
 in the daylight for some considerable time to produce an 
 impression ; but should the time of exposure be much 
 shortened there will not be any picture visible on the 
 
& PHOTOGRAPHIC PROCESSES. 
 
 layer of iodide of silver, although such really exists, and 
 can be developed, or made to appear. This can be effected 
 by placing the plate over mercury heated to about 148 
 Fahr., so that it receives the vapours which arise there- 
 from, when an exact image of the perforated card will be 
 apparent in a very few seconds. There always remains a 
 certain quantity of iodide of silver which has not been 
 altered by light, because it has been protected from the 
 action of this agent by the opaque body which covered 
 . the plate in certain places. If this iodide of silver were 
 not removed, it is easy to understand that it would become 
 changed as soon as exposed to the light ; and therefore 
 it is necessary to dissolve it by a body which has received 
 the name of a fixing agent. Many substances dissolve 
 iodide of silver, such as the various iodide*, cyanides, and 
 alkaline hyposulphites ; but amongst these the most useful 
 is the hyposulphite of soda. 
 
 The Daguerreotype process just described will be per- 
 ceived to essentially consist of a layer of iodide of silver, 
 the use of a developer to bring out the latent picture, and 
 a fixing agent for removing that portion of the iodide of 
 silver not acted upon by the light. 
 
 THE CALOTTPE process was the invention of Mr. Fox 
 Talbot, and, in consequence, is sometimes termed Talbo- 
 type. It consists in spreading, on a sheet of paper, first a 
 solution of iodide of potassium, and then a solution of nitrate 
 of silver. These two bodies, by their mutual reaction, 
 produce a yellowish-white, insoluble powder ; then, by 
 washing the paper in water contained in a porcelain basin, 
 all the excess of nitrate of silver is carried away, and 
 finally there results a paper the pores of which are com- 
 pletely impregnated with iodide of silver. If this iodised 
 paper be exposed to the light, behind a perforated card, 
 the iodide of silver will become black at the places where 
 the light strikes upon it ; or if a very short exposure 
 be given to the paper, on examination by yellow light no 
 image will be perceived. The picture can, however, be 
 developed by immersing the paper in an aqueous solu- 
 tion of gallic acid, mixed with a very small quantity of 
 another aqueous solution of nitrate of silver and acetic 
 acid. This mixture constitutes Mr. Talbot's developer. 
 
INTRODUCTORY. O 
 
 At the end of some minutes the image shows itself, increases 
 in vigour, and becomes very distinct ; the paper is then 
 removed from the basin of gallo nitrate of silver, washed 
 in water, and the iodide of silver not affected by the light 
 is dissolved out with a solution of hyposulphite of soda. 
 
 The two processes of Daguerreotype and calotype, 
 although employing such different substances as metal 
 and paper, nevertheless have many points of resemblance, 
 as in both the pictures are obtained on iodide of silver, 
 requiring development and subsequent fixing ; but when 
 the respective pictures are examined, a very important 
 difference will be perceived in their general aspect. A 
 proof taken by the Daguerreotype will exhibit a counterpart 
 of the original, with all the lights and shades correct. If 
 it be a view taken with the aid of a camera, the sky will 
 appear white, the trees a little darker, and the shadows 
 black as in nature ; and, in the case of a portrait of a person 
 standing before a white wall, the picture of the wall will 
 be white, the hair and features differently tinted, and the 
 dress black ; consequently, it is usual to call this image 
 direct, or positive. 
 
 It is quite different with the calotype picture ; in fact, 
 the view will have a black sky, the trees lighter, and the 
 shadows white ; and, if it were the portrait, the wall black 
 and the dress white ; or, in other words, the picture will 
 in every respect, as to depth of tint, be the reverse of the 
 original, and for this reason is called indirect or negative. 
 
 Figs. 1 and 2 give an idea of these negative and 
 
 Fig. 1. < Fig. 2 
 
 positive images. Thus Fig. 1 represents a black cross on 
 a white ground. If it be reproduced by the Daguerreo- 
 type an exact copy is obtained; whilst if the calotype 
 process be used, the result will be an inverted image, or 
 the cross will be white on a black ground; in fact a 
 B 2 
 
PHOTOGRAPHIC PROCESSES. 
 
 negative image, as shown at Fig. 2. Figs. 3 and 4 show 
 another example of these negative and positive proofs.* 
 
 There are many drawbacks against the employment of 
 the Daguerreotype process ; for instance, the plate pos- 
 sesses a dazzling brightness, which forces the observer to 
 incline himself in some favourable angle to be able to 
 examine the details of the picture ; besides, it must be 
 protected by glass, because the image which it bears on its 
 surface is destroyed by the least friction ; lastly, and this 
 
 Fig. 3. 
 
 is above all its principal disadvantage, it only gives a single 
 image, whilst the other methods furnish an indefinite 
 number. When a negative image is once obtained, it can 
 be employed to produce a series of other images, which 
 will also be reversed in relation to the negative, and con- 
 sequently positives. Take for example Figs. 3 and 4. 
 Suppose Fig. 3 the model to be reproduced, Fig. 4 will be 
 the negative image on the paper. But if the latter be laid on 
 another sensitive sheet of paper, and exposed thus arranged 
 
 * Sec Note 1. 
 
INTRODUCTORY. 5 
 
 to the sun, its rays will pass through the white part& ; and 
 impress the sensitive paper which is underneath, but will 
 be stopped by the black parts ; and thus will the facsimile 
 of Fig. 3 be produced. It will be understood that the 
 same negative Fig. 4 can be used as often as required, and 
 an unlimited number of positives analogous to Fig. 3 thus 
 obtained. 
 
 From the necessity and manner of employing a paper 
 negative to produce the required positive impressions, a 
 very correct idea will be formed of the motives which have 
 
 Fig. 4. 
 
 led photographers to replace paper by a more homogeneous 
 substance ; however fine a surface paper may appear to 
 possess, if it be examined by transmitted light it is always 
 very uneven in texture, which circumstance greatly 
 injures the delicate tints and sharpness of detail in the 
 positive proofs. 
 
 THE ALBUMEN PROCESS. The white of an egg, other- 
 wise called albumen, is a transparent liquid, which, spread 
 
O PHOTOGRAPHIC PROCESSES. 
 
 on a plate of glass, leaves by evaporation a coating as 
 clear as the glass itself, so that when employed as a 
 photographic vehicle the most minute details are preserved 
 with perfect fidelity. 
 
 The manner of operating with albumen is exactly the 
 same as for the negative paper. In the albumen, properly 
 prepared, is dissolved a small quantity of iodide of potas- 
 sium ; this is spread on a well cleaned plate of glass ; the 
 dried glass is immersed in nitrate of silver, exposed to the 
 light in a camera, developed as a proof on paper, and fixed 
 by hyposulphite of soda. 
 
 The advantage that albumen offers over paper, is the 
 production of finer details in the picture. It is not, how- 
 ever, at all an easy or sensitive process, and therefore 
 unsuitable for taking portraits, as at least ten minntes 
 exposure is required, even in a very good light, to pro- 
 duce an impression. 
 
 THE COLLODION PROCESS, which employs a film of 
 collodion spread on glass, possesses all the good qualities 
 of albumen, with the very great advantage of being, at 
 least, sixty times more sensitive, and withal easier of 
 execution. It is this process, and the subjects imme- 
 diately connected therewith, that will be treated upon in 
 the following chapters. 
 
 CHAPTER I. 
 
 THE PLAN FOLLOWED IN THIS WORK. 
 
 IN this chapter it is intended to give a brief summary of 
 the subjects to be subsequently described in detail under 
 their several heads. 
 
 If a little pyroxyline or gun-cotton be immersed in 
 a mixture of about one part in volume of alcohol, and two 
 parts of ether, it will almost entirely dissolve. In order 
 to obtain a sufficiently transparent solution, it must stand 
 for twenty -four hours in a bottle well corked, and then 
 be poured out into another bottle, taking care not to dis- 
 
THE PLAN FOLLOWED IN THIS WORK. t 
 
 turb the thick part which remains at the bottom. This 
 clear liquid is collodion. 
 
 If a small quantity of collodion be poured on a glass well 
 cleaned, the ether and alcohol will evaporate, and leave on 
 the glass a transparent film. This film is very firm, and 
 adheres strongly to the glass ; it is that which serves as a 
 vehicle for the photographic materials; or, in clearer terms, 
 it is that which is destined to form the surface which will 
 retain the photographic image. It may easily be con- 
 ceived that for the purpose of rendering this film sen- 
 sitive to light, iodide of silver must be formed in its 
 texture ; this is done by dissolving iodide of potassium, 
 or some other iodide, in the collodion. 
 
 It is important to choose a proper iodide, but for the 
 present purpose the use of a collodion containing iodide 
 of potassium will suffice to trace what results and changes 
 take place. On a well-cleaned glass plate pour a certain 
 quantity of collodion in such a manner as to cause it to 
 flow over its surface ; then incline the plate, that the 
 excess of liquid may flow off. After the ether and alcohol 
 are evaporated, or, in other terms, after the plate has 
 become dry, a coating of pyroxyline will be obtained ; 
 but this time it will have an iodide intimately mingled 
 with it. 
 
 In proportion as more or less gun -cotton is dissolved 
 in the mixture of ether and alcohol, a liquid of greater 
 or less density is obtained, and consequently the thickness 
 of coating of pyroxyline will also vary on the glass. The 
 proportion of iodide added to the collodion also regulates 
 the quantity which remains on the glass ; from which it 
 follows that it is not a matter of indifference what formula 
 is employed in its preparation : on the contrary, it is 
 necessary to study with the greatest care the relative quan- 
 tities of the. chemical substances which constitute photo- 
 graphic collodion. These quantities will depend upon the 
 temperature, and yet more upon the results desired to 
 be obtained. 
 
 The glass plate having the collodion spread over it, is 
 now sensitised by being dipped into a solution of nitrate 
 of silver, which converts the iodide of potassium into 
 iodide of silver, sensitive to light. 
 
 It need hardly be mentioned that the iodide of silver 
 
8 PHOTOGRAPHIC PROCESSES. 
 
 being affected by light, the preceding operation of sensitis- 
 ing ought to be done in the dark. This word ought not 
 always to be taken literally ; in photography, we under- 
 stand by darkness a light too feeble to affect the sensitive 
 coating. A wax candle is generally used, or ordinary 
 daylight neutralised by a yellow glass; for a glass of 
 this colour prevents any action on photographic sub- 
 stances. 
 
 The sensitised plate now requires to be placed in a 
 camera, an apparatus composed of a box of wood and an 
 arrangement of lenses, which possess the property of 
 forming with perfect accuracy an image of any required 
 object on the sensitised plate. As a general rule, the col- 
 lodion plate is left in this apparatus from ten to twenty 
 seconds, according to the brightness of the object ; it is 
 then removed, and taken back into the dark room. 
 
 If at this moment the collodion film be examined with 
 attention, no trace of an image will be perceived, but it 
 can be made to appear in the same manner as has before 
 been mentioned, by developing with gallic acid. There 
 are also many other developers for bringing out the latent 
 image, such as pyro -gallic acid, proto -sulphate of iron, 
 proto -sulphate of uranium, &c. Whatever the developer 
 may be that is used, it is dissolved in water, and poured 
 over the coated surface of the glass. In a few seconds 
 the image appears as a negative, and the reduction is 
 allowed to proceed ; or, in other terms, the proof left to 
 darken, until it is judged to be sufficiently distinct. The 
 glass is then plunged into water, which removes all soluble 
 substances, then into a fixing solution, such as cyanide of 
 potassium, or hyposulphite of soda, which dissolves the 
 semi-opaque coating of iodide of silver ; finally, the glass 
 is washed in a current of cold water, and dried in the air. 
 
 If the proof be examined by transmitted light, it will 
 be found to be a true negative ; that is to say, supposing 
 a view has been taken, the sky, the white houses, and 
 in general all objects strongly illuminated, are shown of 
 a black colour; while dark objects, on the contrary, ap- 
 pear transparent (Figs. 3 and 4). 
 
 The use of such a negative as before' mentioned, 
 is to give a number of other proofs either upon glass 
 or upon paper ; and if the tints be in good harmony 
 
THE PLAN FOLLOWED IN THIS WORK. 
 
 with the original model, a satisfactory picture will be 
 obtained. 
 
 To understand the above requires a proper compre- 
 hension of the principle, that in spite of the opposition 
 of lights and shades shown in a negative, with respect to 
 a given model, there must nevertheless be preserved a 
 perfect harmony between the tints. This phrase may 
 appear obscure, but a well selected example will make it 
 clear. Suppose a series of ten bands be fixed on a wall, 
 of which the first is absolutely black, the last perfectly 
 white, and the others of intermediate tints. The first will 
 then be black, the second of a greyish black, the third a 
 little less dark, the fourth still less, and thus lighter and 
 lighter, to the perfectly white. 
 
 If a corresponding figure be reproduced on collodion, 
 it will be found, if the nega- 
 tive be a good one, that these 
 ten tints are completely in- 
 verted. In the place of the 
 first black tint of the model, 
 will be one perfectly trans- 
 parent on the negative, whilst 
 the last will be of an opaque 
 black, the intermediate ones 
 having a regular gradation ; for 
 if it were otherwise, a proof 
 taken from such a negative 
 would not represent the true shades of the original model. 
 The Figs. 5 and 6 are intended to show this effect on 
 three bands ; but the result would be analogous for any 
 larger series. 
 
 The conditions necessary to obtain this exactitude are, 
 that the coating of collodion, be of proper thickness, and 
 sufficiently furnished with iodide of silver to yield a de- 
 composition of such intensity as to produce a thick coating 
 of reduced material ; for if the light has not been able to 
 decompose enough iodide in the coating of collodion, a 
 perfect black can never be produced. It follows, then, to 
 obtain an intense negative, there must be employed a thick 
 collodion strongly iodised, and a concentrated bath of 
 nitrate of silver. 
 
 The foregoing are the general details for producing 
 B 3 
 
 Figs. 5 and 6. 
 
10 PHOTOGRAPHIC PROCESSES. 
 
 negatives upon collodion. This process, however, like 
 that of the Daguerreotype, can be made to "give direct or 
 positive proofs at one operation ; but in that case the 
 picture requires to be viewed by reflected, instead of by 
 transmitted, light. 
 
 All the operations necessary to obtain a negative upon 
 collodion require to be performed in rapid succession. But 
 if it be wished to delay the exposure and development 
 of the picture for some time after sensitising the plate, it 
 is re -coated with gelatine, or other suitable substance. 
 The advantage of this method of operating, besides 
 allowing some time to elapse between the exposure and 
 development, is that it does not require the whole of the 
 materials to be taken to the place where it is wished to 
 operate ; and consequently, although much less sensitive 
 than wet collodion, is very applicable for views, &c. This 
 method is known by the name of the Dry Collodion Process. 
 
 Some remarks on the stereoscope, an instrument par- 
 ticularly adapted for viewing photographic pictures, and 
 full details for printing positive proofs from collodion 
 negatives, and a few notes on optical photography and 
 other photographic subjects, will complete the work. 
 
 The following is a list of the subjects treated on in the 
 respective chapters : 
 
 CHAPTER 
 
 II. The Preparation of the Substances required in the manufacture 
 of Photographic Collodion. 
 
 III. The Preparation of Photographic Collodion. 
 
 IV. Cleaning the Glasses. 
 
 Y. The Dark Room, or Photographic Laboratory. 
 VI. Coating with Collodion and Sensitising the Plate. 
 VII. Photographic Cameras, Lenses, &c. 
 VIII. The Glass or Operating Room, and the Rules for taking Views 
 
 and Portraits. 
 
 IX. Development of the Image obtained in the Camera. 
 X. Fixing and Strengthening the Negative Image. 
 XI. Varnishing the Collodion Coating. 
 
 XII. Dry Collodion, including the Collodio-Albumen and Tannin 
 Processes. 
 
 XIII. Positive Collodion Process. 
 
 XIV. The Stereoscope. 
 
 XV. Printing Positive Proofs. 
 
 Notes on Optical Photography and other Photographic Subjects. 
 
PKEPARATION OP SUBSTANCES FOR COLLODION. 11 
 
 CHAPTER II. 
 
 ON THE PREPARATION OF SUBSTANCES REQUIRED IN THE 
 MANUFACTURE OF PHOTOGRAPHIC COLLODION. 
 
 A MIXTURE of alcohol, sulphuric ether, and gun-cotton 
 forms a liquid called plain collodion, to which is added, 
 to render it suitable for photographic purposes, an iodide 
 or bromide ; it is then termed iodised or sensitised col- 
 lodion. 
 
 1. Alcohol. 
 
 Spirits of wine, or alcohol, is a liquid well known, and can 
 generally be procured sufficiently pure for photographic 
 purposes ; it boils at about 172 Fahr., and burns with 
 a bluish flame without leaving a residue. One hundred 
 ounces by weight of alcohol measure about 125 fluid ounces, 
 and 100 fluid ounces weigh about 80 ounces. It should 
 be perfectly clear, transparent, and absolutely free from 
 any floating impurities ; should it be otherwise, it must be 
 carefully filtered. The operation of filtering, applicable 
 to other liquids as well as alcohol, is thus performed. A 
 circular sheet of filtering paper is first folded. in two, as 
 
 Figs. 7, 8, 9, 10. Method of folding Filtering 
 Papers. 
 
 Fig. 11. Apparatus for 
 Filtering. 
 
 represented by Figs. 7 and 8 ; then a new fold is made in 
 the middle, Fig. 9 ; the filter is then opened out, as shown 
 
12 
 
 PHOTOGRAPHIC PROCESSES. 
 
 at Fig. 10, and placed in a funnel, 6, furnished with its 
 support, Fig. 11. The alcohol or other fluid 
 to be filtered, is poured carefully into the fil- 
 tering paper, through which it will pass per- 
 fectly clear. Should the first portion that 
 runs through not be quite bright, it must be 
 returned to the filter. When a very rapid 
 Fig. 12. Plaited filtration is desired, the filter paper may be 
 folded into a number of plaits, as shown at 
 Fig. 12, which affords a larger surface of paper for the 
 liquid to pass through. 
 
 The strength of alcohol is conveniently ascertained by 
 a specific gravity hydrometer. This instrument is formed 
 of glass, Fig. 14. It consists of a glass bulb with a glass 
 stem attached at the top, and a smaller bulb filled with 
 mercury, to serve as a counterpoise at the bottom. In 
 the stem is placed a graduated scale of specific gravities, 
 and the whole is so arranged that when 
 placed in pure distilled water, the instru- 
 ment floats, and the surface of the water is 
 coincident with or I'OOO on the scale. When 
 placed in alcohol or any fluid lighter than 
 water, the hydrometer sinks according to its 
 strength or specific gravity. A test-glass or 
 cylinder, Fig. 13, is used to hold a sample of 
 the alcohol or other liquid to be tested, and 
 care must be taken when the hydrometer is 
 placed in it that it floats perfectly free in the 
 fluid, and that no air bubbles attach them- 
 selves to its surface. The specific gravity is 
 then immediately indicated by noting the 
 degree cut by the surface of the fluid. Alcohol, suitable 
 for photographic purposes, should not have a greater 
 specific gravity than *819. Its best strength is about 
 803 to -810. 
 
 2. Ether. 
 
 It is comparatively easy to procure alcohol of sufficient 
 purity for photographic use, to what it is to obtain pure 
 sulphuric ether. Wlien manufactured on a large scale for 
 ordinary pharmaceutical purposes, there is generally so 
 
 Figs. 13, 14. 
 Hydrometer 
 and Glass. 
 
PREPARATION OF SUBSTANCES FOR COLLODION. 13 
 
 little care taken, that the ether becomes contaminated with 
 eulphovinic acid, aldehyde, or, worse than all, a peculiar 
 principle resembling ozone, which is capable of decom- 
 posing iodides and liberating free iodine, therefore highly 
 detrimental to its photographic action. The formation 
 of this substance is much accelerated by the joint action 
 of air and light ; the knowledge of this circumstance is, 
 therefore, of some importance to photographers, as it 
 indicates a very necessary precaution to be taken to keep 
 ether, and liquids containing it, particularly collodion, in 
 well filled and closed bottles. 
 
 Sulphuric ether is a colourless liquid, and very volatile ; 
 when poured into water it floats about like oil, and a very 
 small quantity is dissolved. It is much lighter than water, 
 100 ounces by weight of ether being equal in volume 
 to 135 ounces by weight of water. Ether is tested as to 
 its strength by the specific gravity hydrometer, in the 
 same manner as described for alcohol on the opposite page. 
 It should have a specific gravity of "750 to *720 to be of 
 any use in photography. 
 
 In consequence of the highly volatile nature of ether, 
 and its vapour being very explosive when mixed with 
 atmospheric air, it is necessary, to prevent accidents, to 
 avoid pouring ether from one vessel to another in a 
 close room, or in proximity to a fire, or flame. As 
 the vapour of ether is much heavier than the air, it 
 naturally tends to fall, and therefore it is a proper 
 precaution to take, when employing ether or fluids con- 
 taining it as collodion, for example by artificial light, 
 to have the source of light situated at some distance 
 above the vessel from which the ether or collodion is 
 poured. 
 
 Ether, if not sufficiently pure for photographic purposes, 
 can generally be made available by the following method 
 of rectification : 
 
 Into a tall bottle, Fig. 15, is to be poured the ether to 
 be purified, together with one-fourth of its volume of 
 water, and the opening closed with a cork ; the whole is 
 then strongly agitated, and left to settle for some few 
 minutes. Two layers of liquid will be perceived, the 
 under layer being water slightly etherised, and the upper 
 ether. The cork is now removed, and the shorter end 
 
14: 
 
 PHOTOGRAPHIC PROCESSES. 
 
 Fig. 16. Fig. 15. 
 
 of an ordinary glass syphon, having a small bore, and 
 previously filled with water, is introduced through the 
 neck of the bottle, and quite to the bottom of the liquid. 
 The smallness of the bore, and 
 keeping the finger over the 
 longer end of the tube, will 
 enable the above to be done 
 with facility, without the water 
 from the syphon running out. 
 The finger being removed, the 
 syphon begins to act, and the 
 etherised water from the bottom 
 of the bottle is quickly drawn 
 off. When the under layer has 
 nearly disappeared, the orifice 
 of the tube is again stopped with the finger, and the 
 syphon removed. 
 
 A fresh quantity of water is now poured into the 
 bottle containing the ether, which is again agitated and 
 drawn off by the syphon as before explained. 
 
 This operation is called " washing," and the ether after 
 this process is called " washed ether." 
 
 If bent glass tubes can be conveniently made or 
 obtained, the following arrangement may be found more 
 convenient than the ordinary syphon, it is shown at 
 Fig. 17 : A, the bottle where the ether 
 and water is shaken together ; it is fur- 
 nished with a good cork pierced with two 
 holes, in one of which is fitted a narrow 
 tube (a) about ths of an inch internal 
 diameter, and in the other, a curved 
 syphon tube (6), of which the shorter 
 end inside the bottle reaches to the 
 bottom. If the cork be properly fitted, 
 it is only necessary to blow slightly 
 through the tube (a) to cause the 
 liquid to rise in the tube (6) and flow 
 over. When nearly the whole of the 
 underlay er of liquid has passed over, the 
 syphon is stopped with the finger, the 
 cork removed, and the fresh quantity of water added, 
 and the operation gone through a second time. 
 
 Fig. 11. Bottle with 
 Syphon. 
 
PREPARATION OF SUBSTANCES FOR COLLODION. 15 
 
 The ether having been well washed, now requires to 
 be dried and distilled ; this is done by pouring the ether 
 remaining in the washing bottle into a distilling vessel 
 containing some few pieces of quicklime. 
 
 A convenient arrangement of apparatus for the distil- 
 lation of small quantities of ether, is shown at Fig. 18 ; 
 where larger quantities are operated on, the glass retort 
 should be replaced by a vessel of zinc or tin plate. A is 
 a small furnace for' charcoal, B a vessel of copper or iron 
 of some convenient form, to hold a small quantity of water, 
 C a glass retort or other vessel, the opening of which 
 is attached, by means of a cork, to a small leaden tube 
 about the thickness of the little finger, and 1 J yards long ; 
 
 Fig. 18. Apparatus lor distilling Ether. 
 
 a portion of this tube is surrounded by another about 
 2 inches in diameter, and f ths of a yard long ; the top and 
 bottom of this tube is closed perfectly water-tight round 
 the smaller tube, it has also an overflow tube (a) at the 
 top part, -and a funnel and tube (6) at the bottom, 
 through which a stream of cold water can be passed 
 from any convenient vessel, as F, and discharged into the 
 receptacle H. The end of the small leaden tube is bent 
 so as to dip into a perfectly clean bottle (G) ; in every 
 other respect the figure will convey a correct idea of the 
 construction of the apparatus. 
 
 When about to be used, each separate part of the 
 apparatus should be perfectly cleaned and washed out 
 
16 PHOTOGRAPHIC PROCESSES. 
 
 with water, and arranged as described and shown in the 
 cut. The glass retort (0) or other vessel, is filled for 
 about one -fourth its volume, with small pieces of quick- 
 lime, and the washed ether poured on to it until two- 
 thirds of the bulk of the retort is filled ; the end of the 
 leaden tube is then attached to the neck of the retort, and 
 the refrigerator E D arranged in an inclined position, 
 and firmly fixed by its support (d) so that the bent end 
 of the tube dips into the mouth of the bottle, G, which 
 is to receive the distilled ether. The whole being thus 
 arranged, a small quantity of water is poured into the 
 vessel B, so that the lower portion of the retort is 
 immersed in it, forming what is called a water bath; 
 some lighted charcoal is now placed in the furnace A, 
 and the water in the vessel B becoming heated, com- 
 municates its heat to the ether in the retort, which begins 
 to evaporate, and in a short time drops of ether appear 
 at the bottom of the leaden tube, and the distillation 
 begins.* The water in the vessel B gets more and more 
 heated as the bulk of ether in the retort diminishes, until 
 no more drops are perceived to fall from the end of the 
 tube ; the fire is now removed, the apparatus separated, 
 and the retort (0) or other vessel at once cleaned out, 
 for should this be delayed, it becomes very difficult of 
 performance. 
 
 The heat of the fire must be kept as much as possible 
 from the bottle (G) containing the distilled ether, and a 
 current of very cold water passed through the refrigerator 
 E D, otherwise the ether vapour is not condensed. Sul- 
 phuric ether, rectified in the manner described, although 
 not absolutely and chemically pure, is nevertheless well 
 adapted for photographic purposes. 
 
 3. Gun-cotton. 
 
 Gun-cotton, also termed " pyroxyline," is nothing more 
 than ordinary cotton combined with peroxide of nitrogen. 
 It can be prepared by plunging cotton wool for a few 
 minutes into concentrated nitric acid, then washed in 
 water and dried; but in order to obtain a good pyroxy- 
 line for photographic purposes, a particular process must 
 
 * See Note 2. 
 
PREPARATION OF SUBSTANCES FOR COLLODION. 17 
 
 be followed, and a rigorous attention paid to each 
 separate detail. Gun-cotton in appearance much re- 
 sembles ordinary cotton, but it is heavier, and its fibres 
 break more easily ; it possesses also a slightly yellow tint, 
 which resembles that of raw cotton as imported into 
 Europe from the colonies. It is insoluble in water, 
 alcohol, pure ether, sulphuret of carbon, or chloroform, 
 but it dissolves in acetate of ethyle and methyle, methylic 
 alcohol, acetone, and also in alcoholised ether. 
 
 Pyroxyline burns with violence when brought in con- 
 tact with any flame ; so much so as in many instances to 
 answer the purpose of common gunpowder. 
 
 The solution of gun-cotton in alcoholised ether is called 
 collodion, and is employed in surgery and photography ; 
 but for this latter purpose it requires to be specially 
 manufactured. 
 
 The following is the method of preparing gun-cotton for 
 photography, although we strongly recommend its being 
 purchased ready made, as photography being now so ex- 
 tensively employed, gun-cotton is prepared on a large 
 scale, and at a low price. 
 
 In a porcelain mortar is placed 2 ozs. of saltpetre in 
 fine powder, and over it is poured 3 ozs. by weight of 
 sulphuric acid of commerce. With the pestle, or a large 
 glass tube, the materials are well mixed, so as to obtain 
 a homogeneous paste. In this is immersed, in successive 
 portions, oz. of carded cotton, free from any mechanical 
 impurities. The cotton is pressed down with the pestle 
 until thoroughly wetted and imbedded in the liquid paste. 
 The mortar is then covered with a plate, to prevent the 
 nitrous vapours which are given off from vitiating the air 
 of the laboratory. It is also advisable to perform this 
 operation, if possible, in the open air. 
 
 The cotton is left in this mixture for ten minutes; 
 the mortar is then placed in an inclined position, and 
 water poured into it, at the same time pressing the cotton 
 with the pestle so as rapidly to remove the excess of acid. 
 After washing for a half minute in this manner, it is taken 
 up with the hands and thrown into a wooden tub filled 
 with water, and well kneaded ; or else held under a water- 
 cock, and constantly worked about, and from time to time 
 pressed strongly between the hands. This washing should 
 
18 PHOTOGRAPHIC PPtOCESSES. 
 
 be thoroughly done, until a portion of the cotton, when put 
 in contact with blue litmus paper,* does not produce a red 
 stain. It is then strongly pressed, and left to dry in the 
 air or in the sun, having previously spread it out thinly, 
 so as to present a large surface to the air. When the 
 cotton is dry it is preserved in glass bottles, well stopped. 
 Gun-cotton, thus prepared, very often gives traces of sul- 
 phate of potass ; but as this substance is absolutely inso- 
 luble in ether and alcohol, it is of no importance. 
 
 Large quantities of gun-cotton should not be bought 
 or prepared at one time, as it appears to be liable to 
 decompose by keeping. 
 
 Gun-cotton, or pyroxyline, can be prepared according 
 to the formula given above from paper, linen, or hemp ; 
 but these preparations have not been sufficiently studied 
 for us to recommend their employment in photography. 
 
 At the end of this volume (JSfote 3) some details are 
 given relative to the manufacture of gun-cotton on a large 
 scale by a mixture of nitric and sulphuric acids. In 
 general, the gun-cotton so prepared is less soluble than 
 that which has just been described ; it, however, yields 
 an excellent collodion, especially adapted for coating large 
 plates, from its being very adherent. 
 
 Gun-cotton was discovered by M. Schonbein, a Ger- 
 man chemist, in 1846. The photographic process which 
 employs collodion as its basis was first described by 
 Mr. Archer, in England, in 1851. M. Schonbein prepared 
 gun-cotton by steeping cotton in monohydrated nitric 
 acid. Afterwards M. Meynier discovered the advantage 
 of using a mixture of concentrated nitric and sulphuric 
 acids, and the method of preparation with saltpetre and 
 
 * Blue litmus paper is turned red by acids ; red litmus paper is turned 
 blue by alkalies. These two papers can be bought ready prepared, or 
 they can be made in the following way : Half a pound of litmus, in 
 small cakes, is boiled in an iron vessel- with one quart of water for some 
 minutes, and then poured through a fine piece of linen, to separate the 
 undissolved portion. This solution is spread over paper by means of a 
 camel's hair brush, and the blue paper thus obtained hung over a cord to 
 dry. To make the red paper, a small quantity of vinegar is added to the 
 foregoing blue liquid until it becomes of a reddish colour. It is best to 
 cover the paper on both sides, and to cut it into small bands, which 
 should be kept in closed bottles, so as to prevent the action of acid or 
 alkaline vapours. 
 
PREPARATION OP SUBSTANCES FOR COLLODION. 19 
 
 sulphuric acid is due to M. Marc Antoine Gaudin, calcu- 
 lator in the Bureau des Longitudes of France. 
 
 In connection with the method of preparing collodion, 
 presently to be described, will be indicated some other 
 important points as further guides to the selection or 
 manufacture of a good gun-cotton. 
 
 4. The Iodides and Bromides employed in the Prepara- 
 tion of Photographic Collodion. 
 
 A great number of iodides, bromides, and their com- 
 pounds have been at various times proposed for sensitising 
 collodion, but the formula most to be recommended is a 
 mixture of iodide and bromide of cadmium. In Note 4 
 will be found some remarks on the employment of the 
 iodides and bromides of potassium and ammonium. 
 
 Cadmium is now easily procured, almost in a pure state, 
 and at a comparatively cheap price. This metal is generally 
 found in commerce in small cylindrical ingots, about four 
 inches in length, and one -fourth in diameter. Its purity 
 can be known by its making a ringing crackling noise 
 when bent, like tin. If it bends with difficulty, and pro- 
 duces no sound when bent, it contains some other metals, 
 usually copper and zinc. 
 
 Iodine is a crystalline substance, having the aspect of 
 black-lead, or plumbago, volatile at a slight increase of 
 temperature, giving off purple vapours, highly corrosive, 
 and irritating to the eyes ; it should always be preserved 
 in glass-stoppered bottles. It is obtained from the ashes 
 of burnt sea-weeds. 
 
 Bromine. This substance is obtained from sea-water, 
 after all the common salt has been removed by boiling. 
 It is a very dense, dark red liquid ; its vapour is highly 
 injurious and corrosive, and, from its great volatility, is 
 always kept under a stratum of water or sulphuric acid, 
 and in glass-stoppered bottles. Both iodine and bromine 
 are easily procured from any chemist. 
 
 Iodide of cadmium is thus prepared : In a glass flask, 
 containing a quart of water, at first put in 8 ozs. of iodine, 
 and immediately after 4 ozs. of cadmium in small pieces. 
 The flask is placed on a stove, moderately heated, in such 
 a manner that the water in the flask shall be kept only 
 
20 PHOTOGRAPHIC PROCESSES. 
 
 warm, not boiling. At the end of a few hours, especially 
 if shaken from time to time, the liquid, from red, which it 
 was at first, will become entirely colourless. Leave it 
 to cool, and then filter. The cadmium that remains may 
 be used for another operation. 
 
 The solution of iodide of cadmium thus obtained, is 
 evaporated in a porcelain capsule. After a certain time 
 crystals will appear in the liquid. It is then placed on a 
 very hot store, where all the water is driven off, and a dry 
 mass obtained. The resulting substance is detached from 
 the capsule with a knife, then reduced to a fine powder 
 in a mortar, and finally preserved in a stoppered bottle. 
 
 The iodide of cadmium thus prepared is of a yellow tint, 
 very soluble in water and alcohol, but less soluble in ether. 
 
 Bromide of cadmium is made by pouring 6 ozs. of 
 bromine into 1 quart of water, contained in a stoppered 
 flask ; 4 ozs. of cadmium, in small pieces, are now added, 
 and the flask closed. This mixture is left for some days, 
 and very carefully shaken from time to time ; the liquid 
 gradually becomes discoloured, from the absorption of the 
 bromine ; when this takes, place it is filtered and evapo- 
 rated to dryness, as described for iodide of cadmium. 
 
 Bromide of cadmium is of a white colour, and less 
 soluble in water and alcohol than the iodide. These sub- 
 stances, when prepared for sale on a large scale, are 
 obtained beautifully crystallised, which may be taken as 
 an evidence of their purity. 
 
 CHAPTER III. 
 
 PREPARATION OF PHOTOGRAPHIC COLLODION. 
 
 As the preparation of photographic collodion requires a 
 considerable degree of nicety in the operations of mea- 
 suring and weighing, it will not be out of place here to 
 make a few remarks relative thereto that may be of some 
 utility to the practical photographer. 
 
 Liquids are measured in glass vessels graduated into 
 
PREPARATION OF PHOTOGRAPHIC COLLODION. 
 
 21 
 
 ounces, drachms, and minims, the indicating signs and 
 relative quantities of which are shown 
 in the following table : 
 
 1 pint contains 20 ounces, ^ xx. 
 
 5 j, or 1 ounce, contains 8 drachms, 5 viij. 
 
 5 j, or 1 drachm, contains 60 minims. 
 
 Three of these graduated glasses 
 will be found necessary one of the 
 shape Fig. 19, to hold 1 pint, and Fig . 2 o. Fig. iy. 
 divided into ounces; another of the Divided Measuring Glasses, 
 same shape, to contain 2 ozs. and divided into drachms, 
 and a small measure, of the form of Fig. 20, holding 
 2 drachms and graduated into minims. When used for 
 measuring liquids, they should be held horizontally, on a 
 level with the eye, and the fluid poured in until its surface 
 reaches the line corresponding with the required figure 
 on the glass. As these graduated glasses have lines cor- 
 responding with each other both at the front and back, the 
 proper position of the measure as regards its level is easily 
 shown. 
 
 \Fig. 21. Table Balance. 
 
 The table balance, Fig. 21, will be found the most con- 
 venient form for weighing quantities up 
 to 2 Ibs. It should have a set of weights 
 from \ oz. to 2 Ibs. 
 
 For weighing smaller quantities, the 
 hand scales, Fig. 22, is required. The pans 
 should be made of glass, and there should 
 be a suitable set of weights, from \ grain 
 to 2 drachms. Glass is the best material 
 for the scale-pans; but if formed of metal, 
 it will be requisite, before proceeding to 
 weigh any chemical, to place a piece of Fifft 22 . Ha nd 
 paper of equal dimensions in each pan, by Scales, 
 which arrangement the whole of the substance is con- 
 
22 PHOTOGRAPHIC PROCESSES. 
 
 veniently removed after weighing, and any injurious action 
 avoided. When fluids are required to be weighed, a 
 glass or other vessel to hold the liquid, is first accurately 
 balanced or counterpoised, and then the weighing done 
 in the ordinary manner. 
 
 The preparation of Iodised Collodion requires the 
 following substances : 
 
 Ether, sp. gr. -720 3 ounces. 
 
 Alcohol, sp. gr. -805 li ,, 
 
 Gun-cotton 16 grains. 
 
 Iodide of Cadmium in powder 18 ,, 
 
 Bromide of Cadmium ,, 6 ,, 
 
 The gun-cotton is first put into a suitable glass bottle, 
 afterwards the iodide and bromide of cadmium and the 
 alcohol. The mixture is then strongly agitated to dis- 
 solve the salts of cadmium, and to open the fibres of 
 the cotton, and facilitate its subsequent solution. The 
 ether is now added, and the whole again well shaken 
 until the cotton is dissolved, when the bottle is closed 
 with a good cork, and left to settle for twenty -four hours, 
 after which the clear and limpid portion is decanted into 
 small glass bottles for use. 
 
 From the circumstance that collodion containing the 
 iodiser as above is liable to decompose, it will generally 
 be found preferable to prepare the collodion and iodising 
 solution separately in the following manner. 
 
 Plain thick Collodion, without iodides or bromides, is 
 first prepared as follows : 
 
 Into a bottle of about one quart capacity is placed 
 
 No. 1. 
 
 Gun-cotton 450 grains. 
 
 Alcohol 7 ounces, 
 
 Ether 25 
 
 These materials are very strongly agitated together, 
 and left to settle for some days. 
 
 A solution of iodide and bromide is also prepared 
 thus : 
 
 No. 2. 
 
 Alcohol - 3f ounces. 
 
 Iodide of Cadmium 154 grains. 
 
 Bromide of Cadmium 54 grains. 
 
PREPARATION OF PHOTOGRAPHIC COLLODION. 23 
 
 The iodide and bromide of cadmium should be ground 
 very fine in a porcelain or glass mortar with a small 
 quantity of the alcohol, then the remainder added, and 
 when the salts are dissolved, the whole carefully filtered. 
 The clear solution must be preserved in a well-stopped 
 bottle. 
 
 To prepare Sensitised Collodion, pour into a four- 
 ounce bottle 
 
 Thick Collodion (No. 1.) 1 ounce. 
 
 Solution of Iodide and Bromide (No. 2.) ... 3 drachms. 
 
 Alcohol 6 drachms. 
 
 Ether If ounce. 
 
 Immediately after the bottle has been well shaken, so 
 as properly to mix the ingredients, the sensitised or 
 iodised collodion is ready for use, but is improved by being 
 kept a few hours after sensitising before being applied. 
 
 Both the plain collodion and the alcoholic solution of 
 iodide and bromide of cadmium can be preserved for any 
 length of time without deterioration, provided they are 
 kept separate and in well-closed bottles ; and the sensi- 
 tised collodion can, therefore, be prepared when required 
 with great facility. 
 
 The formula for sensitised collodion just given will be 
 found to work best at a mean temperature of 60 Fahr. 
 When the weather is very hot a little more alcohol must 
 be added, and the quantity of ether slightly diminished ; 
 and, on the contrary, when the atmosphere is very cold 
 the alcohol may be diminished, and the ether increased. 
 
 When a glass plate is coated with collodion, a larger 
 quantity is poured over its surface than is really required, 
 the surplus being received in a bottle ; it will therefore 
 be easily understood that after a considerable number of 
 plates have, been coated, the proper relative proportions 
 of the constituents of the collodion will have been dis- 
 turbed by evaporation, and that both ether and alcohol 
 must be added to bring it to its normal condition. It 
 must be borne in mind in making the required addition of 
 ether and alcohol, that ether being much more volatile 
 than alcohol, a larger relative proportion will have evapo- 
 rated, and consequently a larger quantity of ether mast 
 be used than of alcohol. 
 
24: PHOTOGRAPHIC PROCESSES. 
 
 If the layer of collodion on the glass appears too thin, 
 a little of the thick collodion, No. 1, must be added ; if, 
 on the contrary, it be too thick, and in consequence does 
 not spread evenly over the glass, it can be diluted with 
 a small quantity of a mixture of two parts of ether and 
 one of alcohol. 
 
 If the collodion film detaches itself from the glass plate 
 after being sensitised in the silver bath, it indicates that a 
 larger proportion of ether is required, or that the gun- 
 cotton employed is not suitable, in which case recourse 
 may be had to a gun-cotton prepared according to the 
 formula given in Note 3, which produces a very adhesive 
 collodion, especially applicable when glasses of large 
 dimensions are employed. 
 
 If too much alcohol be added to the collodion, the film 
 is liable to become detached, and the coating itself has a 
 wavy uneven appearance. If there be too much ether 
 the layer is very adhesive, but it is difficult to get the 
 collodion to spread itself evenly over the plate, especially 
 if it be of any large size. 
 
 Collodion ought to be preserved in well-stopped bottles, 
 but it is indifferent whether bottles with glass stoppers 
 or furnished with good corks be employed ; they ought, 
 however, as much as possible, to be kept quite full, and 
 in the dark. 
 
 Iodised collodion is never good the first day of its pre- 
 paration ; it must be kept for at least two days to acquire 
 all its properties ; neither must it be kept too long, for 
 impressions are then taken with it less rapidly. 
 
 Collodion is very unstable; sometimes without any 
 apparent reason it becomes slow in producing im- 
 pressions ; at other times it changes to a red colour at 
 the end' of a few days. In this latter case recourse ought 
 to be had to a new preparation, and care taken to ascer- 
 tain if the materials previously employed were sufficiently 
 pure. The colour of good collodion is commonly of a 
 very light lemon colour, although sometimes completely 
 colourless. 
 
 A very clear and perfectly settled collodion must 
 always be made use of. The following is an excellent 
 little apparatus for pouring out collodion free from 
 sediment. 
 
CLEANING GLASS PLATES, ETC. 25 
 
 A very tall and narrow bottle must be procured of the 
 form indicated by Fig. 23. The cork a is pierced with 
 two holes made with a round file ; 
 two small glass tubes are fitted to it, 
 of which A goes a little way through 
 the cork, and the other is bent down 
 in the form of H> only one branch is 
 shorter than the other. The longer 
 branch is dipped into the collodion at 
 a short distance from the bottom. 
 After a certain quantity of collodion 
 has been used for several hours, what 
 remains should be poured into the 
 bottle by lifting the cork a, which 
 must be again replaced. The next 
 morning the collodion will be per- 
 fectly settled, and by blowing into 
 the tube A, the clear liquid passes by the tube D a B, 
 from the extremity of which it is received into a proper 
 bottle. 
 
 Care must be taken that the surface of the collodion be 
 lower than the extremity of the tube B ; should it be 
 otherwise the tube must be raised by causing it to pass 
 through the cork, or else the collodion would continue 
 to flow after the required quantity had been decanted. 
 
 CHAPTER IV. 
 
 CLEANING GLASS PLATES, ETC. 
 
 GLASS plates for photographic purposes are employed 
 with ground edges that is to say, the glasses, after 
 being cut with a diamond, are ground on their edges by 
 means of a fine file, aided by oil of turpentine. The 
 object of this operation is to prevent the operator from 
 cutting himself upon the sharp edges of the glass. 
 
 In place of crystal sheet, ordinary patent plate, or 
 even flatted crown glasses may be used, especially for 
 
Zb PHOTOGRAPHIC PROCESSES. 
 
 the smaller-sized (under half- plate). Patent plate being 
 more perfectly polished than flatted crown, is also more 
 easily cleaned, and therefore preferable. 
 
 Whatever be the kind of glass employed, the following 
 is the method which should be pursued in cleaning the 
 plates whether they have been used before or not : 
 
 A mixture of equal quantities of nitric acid and water 
 is made, and the glasses covered therewith on both sides 
 by the aid of some cotton-wool fastened to the end of a 
 stick ; and as each plate is successively treated in this 
 manner, they are placed against the wall to drain. 
 
 Instead of nitric acid a solution of carbonate of potash, 
 of the strength of one pound to one quart of water, may 
 be advantageously employed. The liquid acts energe- 
 tically upon plates that have been previously used, and 
 is free from the objection to which nitric acid is open, 
 namely, that of staining the hands yellow. 
 
 It is always a good plan to clean a number of plates at 
 the same time as many as twenty, for instance because it 
 is necessary to allow the alkaline or acid solution to act for 
 at least an hour. The plates are then submitted to the 
 action of a strong current of water, and rubbed at the same 
 time on both sides with a sponge, in order to remove all 
 impurities. It is almost unnecessary to add that they are 
 finished by allowing the water to flow in all directions, 
 copiously, on the inclined plate, to carry off every trace of 
 dust. The glasses are then placed in a grooved frame, similar 
 
 Fig. 24. Support for Cleaned Plates. 
 
 to Fig. 24, which precludes the necessity of description, 
 where they are allowed to drain and dry. The photo- 
 
CLEANING GLASS PLATES, ETC. 
 
 27: 
 
 grapber should furnisli himself with several of these 
 JraiDing frames of different sizes, for they will be found 
 very convenient. 
 
 The glass having been cleaned, is not yet sufficiently 
 pure to receive the collodion : it is further necessary to 
 resort to a more complete polishing. For this purpose an 
 oak plate -holder, of the form A B, Fig. 25, and of 
 suitable size should be used. At the end B is placed a 
 piece of wood about the thickness of a crown -piece. A 
 
 Fig. 27. Fig. 26. Fig. 25. 
 
 Tripoli Bottle and Plate-holder. 
 
 groove, c d, admits of a second piece, e, fixed underneath 
 by a clamp-screw, Fig. 27, to fix the plate a b, of any 
 size within the dimensions of the plate-holder. 
 
 In addition to this, there should be near at hand a box 
 containing powdered tripoli, and a bottle furnished with 
 a tube of small bore, Fig. 27, containing alcohol. The 
 glass being fixed on the plate -holder, Fig. 27, is well 
 dusted with tripoli, a few drops of alcohol are poured 
 upon it, and then, by means of a little cotton -wool, or 
 papier Joseph, the mixture is rubbed all over, carefully 
 avoiding contact between the fingers and the glass. 
 The rubbing is repeated, but without pressing too hard, 
 until the alcohol has entirely evaporated, and the plate is 
 dry. The excess of adherent tripoli being removed by a 
 c 2 
 
28 PHOTOGRAPHIC PROCESSES. 
 
 dry linen cloth set apart for this especial purpose, the 
 final polish is given with an exceedingly dry buckskin or 
 chamois leather, which should also be used exclusively for 
 this operation. 
 
 The plate is then removed from the plate -holder, its 
 edges and back wiped, and placed in a grooved plate - 
 box. Care should be taken that that side of the glass 
 which has been polished for the reception of the collodion 
 film, should in each case face the same way, in order to 
 avoid errors in pouring on the collodion. 
 
 The plates should never be cleaned more than twelve 
 hours before using, especially if the box in which they 
 are contained is likely to be carried about, as in that case 
 they would again become covered with minute particles 
 of dust 
 
 CHAPTER V. 
 
 ON THE DARK ROOM, AND PHOTOGRAPHIC LABORATORY. 
 
 IN the practice of photography, three different rooms are 
 necessary : one well lighted, in which the sitter is placed ; 
 another of commodious dimensions, which serves the 
 purpose of a laboratory ; and a third made quite dark, in 
 which are performed all those operations which may not 
 see the light of day. 
 
 The laboratory should be of such dimensions as are 
 adapted to meet the wants of the photographer. Amateurs 
 generally take plenty of room, because in most cases it 
 costs them nothing ; but professional photographers are 
 oftener obliged to content themselves with a small apart- 
 ment, which frequently serves the double purpose of dark 
 room and laboratory. 
 
 However this may be, it is best to have a large room, 
 where preparations can be made, positive proofs printed, 
 &c., on the ground floor, well furnished with drawers 
 and tables. 
 
 The dark chamber ought to be, on the contrary, very 
 
DARK ROOM, AND PHOTOGRAPHIC LABORATORY. 29 
 
 simple. Two or three tables are sufficient, and the light 
 ohould either be entirely excluded by pasting black paper 
 over the windows, and the operations conducted by the 
 light of a candle or a gas jet, surrounded by a square 
 lantern of yellow glass, or else, as often preferred, the dark 
 room is so arranged that the light comes exclusively 
 through a frame of yellow glass about 10 inches by 8 inches, 
 and this covered with a sheet of very thin white paper, in 
 order to impede the passage of the direct solar rays. A 
 hinged frame is fitted in front of this square of yellow 
 glass in such a way as to admit of its being totally or 
 partially covered, in order to diminish or increase the 
 amount of illumination at pleasure. 
 
 Fig. 28. Dark Chamber. 
 
 It is necessary to select glass of a deep yellow colour, 
 and avoid the paler kinds. 
 
 The drawing (Fig. 28) represents the dark chamber 
 which has been used for many years by M. Monkhoven. 
 
 The entrance is at the bottom of the room, and the 
 door, for greater security, covered with a black drapery. 
 A cistern of water, furnished with a tap, supplies the 
 necessary means for washing, and underneath this is 
 
30 PHOTOGRAPHIC PROCESSES. 
 
 placed the sink, with a pipe to convey the waste water 
 outside. On one side should be placed the dishes used 
 for nitrate of silver bath, and for sensitising albumenised 
 paper, and on the other those which appertain to fixing, 
 and other operations incompatible with the nitrate of 
 silver solution. Shelves should also be fitted up to 
 support funnels while filtering, bottles, &c. 
 
 A second reference to Fig. 28 will show the arrange- 
 ment by which the amount of light is regulated; it will 
 be seen, in fact, that by lowering the yellow frame, which 
 is shown in that position in the drawing, the room 
 becomes inundated with light. This frame need be 
 closed only when the plate is immersed in the nitrate 
 of silver bath, and during the development of the image. 
 When the required intensity has been attained in the 
 last operation, the plate is washed and the frame lowered 
 in order to see more clearly. If the sun shines on this 
 window, it is absolutely necessary to paste over it some 
 thin paper to stop the too direct rays. 
 
 CHAPTER VI. 
 
 COATING WITH COLLODION AND SENSITISING THE PLATE. 
 
 THE nitrate of silver bath is prepared by dissolving 
 Pure Nitrate of Silver 2 ounces. 
 
 IN 
 
 Distilled or Bain Water 24 ounces. 
 
 This liquid is filtered and poured into a gutta-percha 
 tray. The collodion, spread upon the glass, is plunged into 
 the nitrate of silver bath ; the film whitens by the trans- 
 formation of the iodide of cadmium into iodide of silver, 
 which is sensitive to light, and it is in this state that it 
 should be exposed in the camera. 
 
 Such is a general statement of the process to be now 
 described somewhat in detail. 
 
COATING AND SENSITISING THE PLATE. 
 
 31 
 
 The collodion ought to be contained in a bottle with 
 a wide month (Fig. 29), which month should always 
 be carefully cleaned before pouring the col- 
 lodion on the glass. 
 
 The box containing the cleaned glasses 
 being placed in the dark chamber, a plate is 
 withdrawn, and the dust removed from the 
 polished side by means of a large badger-hair 
 brush ; then holding the plate by one corner 
 (Fig. 30), in the right hand, the collodion is 
 poured upon it from the left hand, com- 
 mencing at the corner B. It is then allowed 
 to flow by inclining the plate from left to right, 
 and finally draining back into a separate 
 bottle from the corner D, Fig. 31. If, at this moment, 
 the plate be examined in a particular light, it will be seen 
 that it is covered with an infinity of small ridges in the 
 
 Fig. 29 
 
 Fig. 30. Coating tiie Plate. 
 
 direction B D (Fig. 30) ; but on inclining the plate 
 rapidly from left to right, these ridges will disappear. 
 As soon as this happens, the plate is ready to be immersed 
 in the nitrate of silver bath ; but it is always advisable 
 to wait a few seconds (and how many, experience alone 
 can indicate precisely), so that the film may be suffi- 
 ciently " set." There are certain characteristics by which 
 it may be determined if the right moment has arrived for 
 sensitising the plate ; these are : 
 
 1. If the plate is immersed in the bath before the 
 
32 
 
 PHOTOGRAPHIC PROCESSES. 
 
 collodion has been allowed time to " set," the film will 
 become detached in fragments ; and, in this case, it will 
 be necessary to filter the bath. 
 
 2. If the immersion take 
 place at the right time, the film 
 whitens gradually. 
 
 3. If, on the other hand, the 
 film be allowed to become too 
 dry before immersion, it 
 whitens instantly, and a good 
 proof is never obtainable under 
 these circumstances. 
 
 Up to a certain point it is 
 not difficult to determine when 
 the plate should be immersed 
 in the nitrate of silver bath. It 
 will be found if the plate is 
 looked at in a certain light, that 
 it has assumed a dull, un- 
 polished appearance. This, 
 which is the right moment 
 for immersion, will be arrived 
 at in summer probably in about 
 twenty seconds, while in winter it will probably take 
 sixty seconds. 
 
 Nitrate of silver bath is very easy to 
 prepare. It is quite as well for those 
 whose operations are conducted on a 
 somewhat extensive scale to have a 
 considerable quantity of bath solution, 
 and keep it in a large bottle to which is 
 adapted a funnel and filter, Fig. 32. 
 The same filter will last a long time ; 
 and, on leaving work, the nitrate of 
 silver bath whicli has been used during 
 the day is poured into the filter, and in 
 this way a solution in proper condition 
 is always maintained at hand. 
 
 . 32. Apparatus for For the nitrate of silver bath, dishes 
 fi %1ir N Bl r th. e ' in gutta-percha, porcelain, or wood with 
 glass bottoms, are used, Figs. 33, 34, 37. 
 Gutta-percha dishes are, perhaps, most frequently em- 
 
 Fig. 31. Receiving the Collodion 
 into a separate Bottle. 
 
COATING AND SENSITISING THE PLATE. 
 
 33 
 
 Figs. 33 and 34. Dishes in 
 
 Porcelain and Wood with Glass 
 
 Bottom. 
 
 ployed,* but as vertical baths in glass and gutta-percha 
 are also used, we shall say a few 
 words in reference to them. 
 
 The reason why we recom- 
 mend a gutta-percha dish in 
 preference to one in porcelain 
 is, that the film itself can be 
 better seen, as also the impuri- 
 ties which float in the solution. 
 
 There are several methods of 
 immersing the plates in the 
 nitrate of silver bath ; and as 
 this is one of the most impor- 
 tant points in the present chapter, we will pause to con- 
 sider it somewhat in detail. 
 
 The dish containing the nitrate of silver bath being 
 much larger than the plate, 
 is raised at one end, Fig. 38, 
 in order that the solution 
 shall accumulate at the op- 
 posite end ; the plate, pre- 
 viously coated with collo- 
 dion, is placed against the other edge, and held there by 
 means of the finger or a silver wire hook; lowering then 
 the plate by a continuous motion, and allowing the dish at 
 the same time to assume the 
 horizontal position, the liquid 
 flows at once, and without 
 stopping, over the whole of the 
 plate : after this the dish 
 should be raised and lowered 
 during a minute or so. Then 
 introducing underneath the 
 plate a hook made of flat- 
 tened silver wire, Fig. 35, and 
 by its means withdrawing the 
 plate from the bath, it will be 
 seen to be covered by a num- 
 ber of veins which show that the nitrate of silver bath 
 
 Fig. 37. Gutta-percha Di.h. 
 
 Figs. 35, 36, 39, 
 
 * This remark is correct only as far as regards the practice of conti- 
 nental photographers, in England glass and porcelain baths are always 
 employed. 
 
 c 3 
 
PHOTOGRAPHIC PROCESSES. 
 
 has not thoroughly penetrated the film, and that, there- 
 fore, the plate should be raised and lowered alternately 
 until the silver solution flows evenly and smoothly over 
 the whole surface of the film. 
 
 It is at this point that the plate should be withdrawn, 
 the fingers being covered with India-rubber finger-stalls, 
 
 in the absence of which 
 box -wood forceps, or an 
 American clip, should 
 be used, as the nitrate 
 of silver blackens the 
 hands very strongly 
 (Note 5). The plate 
 is allowed to drain from 
 the excess of adherent 
 nitrate of silver solution, 
 and is then placed in 
 the camera frame. 
 
 This method of ope- 
 rating requires only a 
 small quantity of nitrate 
 of silver bath solution, 
 which is accordingly 
 exhausted in a propor- 
 The plan we are about to describe 
 
 Figs. 40, 41. Vertical Glass Bath. 
 
 tionately shorter time. 
 
 requires, on the contrary, a large bulk of solution, which 
 
COATING AND SENSITISING THE PLATE. 
 
 has the advantage of becoming very slowly exhausted. 
 Moreover, a vessel may be used which is only just large 
 enough to allow the plate to be immersed and withdrawn 
 with freedom. 
 
 The solution is contained in a vertical bath, either of 
 glass or gutta-percha, Fig. 40 ; and by means of a hook 
 or dipper of gutta-percha, which is introduced on the 
 lower side of the vessel, the plate is immersed by one 
 continuous motion into the fluid, raising and lowering 
 it alternately as before. The plate is finally withdrawn 
 ready for exposure, when the ridges or lines thereon have 
 disappeared. In Note 6 are given details for the prepa- 
 ration of nitrate of silver bath. 
 
 Another plan we can much recommend is as fol- 
 lows : Two silver hooks are first procured, made oi 
 flat sheet silver, and bifurcate, of the shape shown in 
 Fig. 37. The nitrate of silver bath being contained in a 
 dish (Fig. 42) of gutta-percha, the plate is held between 
 the two hooks, the film 
 being uppermost, and 
 plunged at one stroke 
 beneath the liquid, tak- 
 ing care at the same 
 time that one end is 
 immersed before the 
 other, for unless this be 
 done the liquid will spirt 
 out of the dish. The 
 plate being once fairly 
 covered by the solution, 
 one of the hooks is re- 
 moved ; and with the 
 other the plate is raised 
 and lowered, in order to 
 get rid of- the veins or greasiness of which we have spoken 
 above. 
 
 Instead of two hooks, it may be found more advan- 
 tageous to use the two combined in one, as shown in 
 Fig. 42. We may observe, in passing, that the silver 
 hooks may be replaced by others made of whalebone. 
 In order to make these, it is necessary to hold them in 
 the flame of a spirit-lamp until they bend, and to allow 
 
36 PHOTOGRAPHIC PROCESSES. 
 
 them to cool, maintaining pressure in the proper curve 
 by means of the fingers until quite cold. 
 
 Whichever method is followed in immersing the plate 
 in the nitrate of silver bath, it is indispensably necessary 
 that it be the result of one steady and continuous motion; 
 for if this be not the case, lines will be formed upon the 
 film, which will become apparent very soon in irreparable 
 stains. 
 
 To preserve the hands from the action of nitrate of 
 silver, some amateurs use India-rubber finger-stalls, or 
 gloves of the same material ; but such apparatus will be 
 found very inconvenient, and those who intend to be suc- 
 cessful in photography should make up their minds before 
 going into it, to sacrifice the delicacy of their hands and 
 the whiteness of their shirt-cuffs. 
 
 We presume it is hardly necessary to observe that, at 
 the time of sensitising the plate, the room should be made 
 quite dark an operation easily accomplished by moving 
 the shutter in front of the yellow glass until the light is 
 almost entirely excluded. With a little practice this will 
 be found comparatively easy. 
 
 As soon as the plate is placed in the camera-back, the 
 window and door may be opened, and the bath covered 
 with a plate of glass, in order to preserve it from dust. 
 
 CHAPTER VII. 
 
 PHOTOGRAPHIC CAMERAS, LENSES, ETC. 
 
 THE common camera-obscura is supposed to have been 
 discovered by Baptiste Porta, about the year 1590. It 
 may be simply described as a box, at one end of which 
 is fixed a piece of ground glass, and at the other a convex 
 or magnifying -glass, mounted in a sliding tube to regulate 
 the focus. 
 
 All convex or concave glasses are called lenses; the 
 focus of a convex glass or lens is the distance between 
 
PHOTOGRAPHIC CAMERAS, LENSES, ETC. 37 
 
 the glass when exposed to the sun, and the point or spot 
 of light where the rays unite (Fig. 43). (See Note 6.) 
 
 If the distance between the A 
 
 magnifying lens and the ground 
 glass of an ordinary camera, be 
 regulated to the focus as de- 
 scribed, and the lens directed 
 towards some distant objects, it 
 will be seen, on so shading the 
 ground glass with a black cloth Ftg ' 43> 
 
 placed over the head as to prevent any lateral rays of 
 light falling on it, that the image of those distant objects 
 are clearly represented reversed on the ground glass. If 
 the camera be now directed to some near objects they 
 will not appear distinct, and the lens will require to be 
 drawn out further from the ground glass before they are 
 shown with perfect sharpness. This adjustment of the 
 lens is called focussing the image. 
 
 It will be found impossible, however, to focus the 
 whole of the objects perfectly ; there will always be cer- 
 tain parts of the picture which want distinctness. But if 
 a piece of cardboard, having a small hole in it, be placed 
 & short distance in front of the lens, the image on the 
 shaded ground glass will become much more distinct 
 and sharp, or, in other words, the picture can be better 
 focussecl. Any similar arrangement to that described is 
 called a stop or diaphragm. 
 
 The foregoing remarks will explain the principles and 
 construction of the photographic camera, which essentially 
 
 Fig. 44. Ordinary form of Photographic Camera. 
 
 consists of two parts the lens or objective, and the box 
 or camera. However, it will be easily understood that 
 
38 
 
 PHOTOGRAPHIC PROCESSES. 
 
 these two apparatuses, to be rendered suitable for the 
 various purposes of photography, must of necessity re- 
 quire more special and compli- 
 cated construction than has been 
 described. 
 
 The ordinary form of a photo- 
 graphic camera, Fig. 44, consists 
 of a box, B, in which slides 
 another box, A, holding the frame 
 C with the ground glass. For 
 the purpose of fixing the sliding 
 part A, a board, D, is fastened to 
 the box B in which is a groove, 
 as shown in the drawing. On 
 the lower side of the box A is 
 fixed a plate with a thumb-screw 
 passing into the groove. Thus, 
 within certain limits, the two 
 boxes A and B can be adjusted to 
 various lengths, and fixed at the 
 required focus by the aid of the 
 thumb-screw. The lens is placed 
 in front of B. 
 
 This form of camera has gene- 
 rally a single sliding-box, A ; but 
 sometimes, however, for the sake 
 of portability, they are constructed 
 with several slides. The mate- 
 rial of which these cameras are 
 made is usually mahogany or 
 walnut wood. 
 
 The tripod, or camera stand, 
 for supporting the camera, is 
 usually of two kinds one for 
 travelling, the other for use in 
 the operating room for portraits, 
 &c. 
 
 The travelling stand, Fig. 45. 
 
 consists of a strong wooden or 
 I*. 45. Tripod Stand. ^j ^^ ^ ^.^ ^ 
 
 made to slip three feet, which for greater strength and 
 firmness are made double. These feet for convenience in 
 
PHOTOGRAPHIC CAMERAS, LENSES, ETC. 
 
 travelling, can easily be doubled up, and removed from 
 the triangle by unscrewing the joints. 
 
 There are many different models of tripod stands for 
 travelling, but they are all more or less on the principle 
 of the one just described, and are made lighter or stronger 
 as may be required for the size of camera. A black 
 
 Fig. 46. Stand for Operating Room, and Camera for " Cartes de Visite." 
 
 cloth, so constructed as to cover over the extended tripod 
 stand, forms a convenient dark chamber for changing 
 sensitised glasses from or to the camera back when dry 
 collodion plates are employed. 
 
 The stand used in the operating room or studio, not 
 
PHOTOGRAPHIC PROCESSES. 
 
 requiring to be moved any distance from place to place, 
 may be of a much stouter and heavier construction than 
 the ordinary tripod stand. The form of camera stand repre- 
 sented Fig. 4(5, combines solidity with facility of adjust- 
 ment. The upper board supports the camera, and in order 
 to allow of a tilting motion is connected with two half 
 circles of wood, which can be fixed in position by a thumb- 
 screw to an upright sliding frame, moving in a socket of the 
 firm tripod stand. This sliding frame serves to adjust the 
 height of the camera. Sometimes this form of stand has 
 a winch, with rack or chain, to facilitate the raising and 
 lowering of the camera. This addition is very convenient, 
 especially when a heavy camera is employed. 
 
 A convenient form of camera for travelling, and suit- 
 able for plates 12 inches by 10 inches, and larger sizes, is 
 represented at Fig. 47. B is a fixed box, pierced in front 
 with a round hole, to which is attached the lens. Under- 
 neath, and on the side (c) are two pieces of brass, in each 
 of which can be fixed a thumb-screw, as seen at a. The 
 sliding body A has also two similar pieces, one at d, the 
 other underneath, each having a thumb-screw. The top 
 of the tripod (which is seen in the figure) has a hollow, 
 in which a long piece of wood b can be fixed ; this has a 
 groove in the middle, to admit the two thumb -screws. 
 
 Fig. 47. Camera without a Tail-piece. 
 
 By this arrangement, on turning the screw a, a very 
 great degree of firmness is given to the part B of the 
 camera ; also to the tail-board 6, and the top of the 
 tripod. The sliding body A can be drawn out or in, 
 and fixed as the operator wishes. The instrument can 
 also be used on its side (the two pieces of brass which 
 
PHOTOGRAPHIC CAMERAS, LENSES, ETC. 
 
 41 
 
 are seen at c and d serve for this purpose), enabling up- 
 right views to be taken with the same facility as long ones. 
 
 This form of camera is more convenient than the ordi- 
 nary form, Fig. 44, especially for taking large views ; 
 besides which, the immoveable tail-board of the model, 
 Fig. 44, prevents its being conveniently used on the side 
 for upright pictures. 
 
 Another form of camera, suitable both for the operating 
 room and for travelling, is represented, Fig. 48. It will 
 
 A. 
 
 Fig. 48. Bellows-body Camera. 
 
 be found extremely light and portable. The construc- 
 tion of this form of camera will be easily understood from 
 the cut. M is a square bellows body, connected with the 
 wooden frames A, a. The frame A, holding the lens, is 
 firmly fixed to a board n, n, which can be lengthened or 
 shortened at will. The frame a holds the ground-glass 
 frame and dark slides. 
 
 Whatever may be the form of camera employed, the 
 general principles to be observed in its use are the 
 same. For the purpose of illustration, suppose a camera 
 mounted , on its stand, as shown in Fig. 55, p. 49, and 
 directed towards a person who stands for a model. On 
 drawing out the sliding body more or less, a point is 
 reached where the proper focus is obtained. As before 
 mentioned, the head of the operator and the top of the 
 camera must be covered with a black cloth, so that the 
 sharpness of the image on the ground glass can be properly 
 examined. Fig. 55 represents an operator focussing a person 
 who is placed before him. If the ground glass be replaced 
 
42 
 
 PHOTOGRAPHIC PROCESSES. 
 
 Fig. 9. Camera, or Dark Frame. 
 
 by a glass plate, covered with sensitised collodion, an image 
 will be obtained representing the model. The proper 
 placing of the sensitised plate is accomplished by means 
 of a frame represented in Fig. 49, and which is always 
 
 sold with and forms part of 
 the camera. This frame, or 
 camera back, is represented 
 open, in order to make the 
 figure better understood. The 
 glass plate, coated with collo- 
 dion, after having been taken 
 out of the silver bath and well 
 drained, is placed in the ca- 
 mera frame, with the layer of 
 collodion towards the shutter 
 a (which has been previously 
 closed) ; then the door b is 
 shut and fastened with hooks, 
 so that the sensitised layer 
 is thus preserved from the 
 light. The ground-glass frame is then removed from 
 the camera, and the frame (Fig. 49) put in its place. 
 If the thin sliding board or shutter a be now raised, the 
 sensitised surface of the glass plate, being exactly in the 
 same position as occupied by the ground glass, receives the 
 same image. When it is thought that the light has acted 
 long enough, the shutter a is closed, the frame removed, 
 and taken into the dark room, where, on opening the door 6, 
 the glass plate is removed, and submitted to an operation 
 to be described under the title of developing the image. 
 
 The inner portion of the frame that 
 holds the sensitised plate has project- 
 ing corners of silver wire, so arranged 
 that the plate only touches at these 
 parts. Thus the woodwork of the 
 frame is in a great measure protected 
 from the corrosive action of the nitrate 
 of silver; and if the precaution be 
 taken of placing a piece of blotting - 
 
 Fig. 50. Glass Frame. P a P er n the lower Comers and back of 
 
 the plate, previously to closing the door 
 6, the risk of drops of nitrate of silver injuring the frame, 
 
PHOTOGRAPHIC CAMERAS, LENSES, ETC. 
 
 and falling during its transport from the dark chamber 
 to the operating room, will be avoided. 
 
 With a camera of a certain size it is very often required 
 to take smaller pictures, as well as the full size the lens 
 will produce. This is accomplished by having some extra 
 frames of wood (Fig. 50) fitting into the larger frame, and 
 carefully adjusted, that when the 
 plate is placed in one of these extra 
 frames its surface shall be exactly 
 coincident with the position of the 
 ground glass upon which the focus 
 was obtained ; if otherwise, it would 
 be impossible to produce a sharp 
 and distinct picture. 
 
 The glasses employed in photo- 
 graphy are usually of patent plate, 
 although good ordinary glass may 
 be employed for very small sizes. 
 The glass plates are kept in grooved 
 wooden boxes (Fig. 51). 
 
 There are two kinds of photographic lenses those 
 called single lenses, for views ; and double, or combination 
 lenses, for portraits. 
 
 The following are the diameters and focal lengths of 
 portrait and view lenses suitable for the various sized 
 glasses usually employed : 
 
 51 - Plat9 Box - 
 
 FOR PORTRAITS. 
 
 Size of Pictures. 
 Inches. 
 
 Ninth size . . . 
 Quarter plate . . 
 Ditto for rapid action 
 Third size ditto 
 Half plate ,. . . 
 Whole plate . . 
 
 3 b , 
 
 5 
 8$ 
 
 y2 
 
 1 
 
 T 
 
 4 4 
 
 Diameter of Lenses. 
 
 Focal Length. 
 
 Inches. 
 
 Inches. 
 
 . it 
 
 3J 
 
 : | : 
 
 5^ 
 
 
 7 
 
 '. si 
 
 7 
 9J 
 
 FOR PORTRAITS AND GROUPS. 
 
 Size of Pictures. 
 
 Inches. 
 
 9 by 7 
 
 10 8 
 
 12 10 
 
 15 12 
 
 Diameter of Lenses. 
 Inches. 
 
 a 
 
 Focal Length. 
 Inches. 
 
 13 
 15 
 19 
 
44: PHOTOGRAPHIC PROCESSES. 
 
 FOR VIEWS. 
 
 Size of Pictures. Diameter of Lenses. Focal Length. 
 
 Inches. Inches. Inches. 
 
 6 by 5 ... If ... 8 
 
 7 ,, 6 ... 2 ... 10 
 9 7 ... 2| ... 14 
 
 12 10 ... 3 ... 16 
 
 16 12 ... 4 ... 24 
 
 The single, or view lens, is composed of an achromatic 
 lens, mounted in a tube of brass (Fig. 52), as shown in 
 the figure. D, the brass cover 
 of the lens. F, a small brass 
 tube, holding diaphragms of 
 various sizes. 0, the brass tube, 
 having the lens at A screwed 
 within it, and also furnished with 
 an outside screw, which allows 
 the whole mounted lens to be 
 
 52. Single, or View Lens. fixed t() the Hng Qf m ^ ^ 
 
 which is attached to the front of the camera. 
 
 The view lens is used in the following manner : It 
 is fixed to the camera by being screwed into the brass 
 ring ; the cover D is removed, when the image may be 
 focussed. All the diaphragms should be removed, except 
 the one to be employed. The smaller the opening of the 
 diaphragm, the sharper the image ; but then a longer 
 time will be required to produce an impression. Thus, 
 a diaphragm of J inch requires four times as long exposure 
 as one of -J- inch ; but then the picture produced is much 
 sharper. It is thus that the operator can, when required, 
 sacrifice sharpness of detail for rapidity of action. 
 
 The lens requires from time to time to be cleansed with 
 a soft wash-leather ; but in remounting the same in its 
 cell, it is of the greatest importance that the convex side 
 of the lens should be towards the sensitive plate.* 
 
 The compound, or portrait lens, is composed of a 
 greater number of lenses. It has a compound lens in 
 front, which is very thick, being formed of two cemented 
 together, like the view lens, and two other lenses at the 
 
 * View lenses are sometimes mounted, with the diaphragms or stops 
 fixed in the large tube holding the lens, which either slides in another 
 tube or is actuated by rackwork, to facilitate the obtaining a correct focus. 
 
PHOTOGRAPHIC CAMERAS, LENSES. ETC. 45 
 
 back. Whenever the lenses are removed to be cleaned, 
 or for any other purpose, it is important that they be 
 replaced in exactly the same order as when purchased, 
 otherwise the picture produced can never be good and 
 sharp. Fig. 53 shows the form of the double, or com- 
 
 Fig. 53. Double, or Compound Lens. 
 
 pound lens. D is the cover, or cap ; B G, a double tube, 
 sliding one over the other, capable of being adjusted by 
 turning the milled head F connected with the rackwork. 
 Its use is, after the focus has been roughly obtained, by 
 drawing out the sliding body of the camera, to finally 
 adjust the same with the greatest ease and nicety. C is 
 a portion of a larger tube, adapted to screw upon the 
 tube B, and serves to protect the lens from lateral rays 
 of light : B, A, the ends where the lenses are fixed. 
 G, the tube, having a screw at the end for the purpose of 
 attachment to the ring E. This ring of metal is fixed by 
 screws upon the front of the camera. H, a diaphragm, 
 or stop, fitting the interior of the tube 0. 
 
 The above are the chief points of difference between 
 the two varieties of lenses known as the single and 
 double. The brass mountings of both forms are blacked 
 inside, to prevent internal reflection, and should this dull 
 black coating be at any time ren- 
 dered im'perfect, it can be repaired 
 by the application of a mixture of 
 lamp-black and gum -water.* 
 
 * In the most recently improved form 
 of compound lens, the sliding body is pierced 
 so as to allow a series of diaphragms, or 
 stops, to be introduced between the two 
 lenses, as shown in the illustration, Fief. 54. 
 
 mi 
 
 1 his arrangement is more correct in prin- 
 ciple, and produces better results, than the simple external stop. 
 
4:6 FHOTOGKAPH1C PKOCESSES. 
 
 With respect to the optical differences of these two 
 forms, and their special uses, it is to be noted that 
 the single lens, although of the same size as the double 
 combination, does not give so brilliant an image upon 
 the ground glass, because the diaphragms intercept an 
 enormous quantity of light. The double lens, on the 
 contrary, has two. lenses, combined in such a way that a 
 diaphragm is not necessary ; consequently, the images pro- 
 duced are well illuminated. By stopping off a single lens, 
 the sharpness of the image is rendered perfect, whereas 
 with the double combination such a degree of sharpness 
 cannot be obtained ; therefore the first is employed for 
 views and buildings, and the latter for portraits. 
 
 Another consideration also influences the selection. 
 It is easy to be understood that a sensitive coating is 
 impressed more easily in proportion to the brilliancy of 
 the light striking upon it. Thus, a lens of 3 inches in 
 diameter, with J inch stop, will require one hundred times 
 longer exposure than a double combination of lenses of 
 the same diameter to produce the same picture. Now, is 
 it not easy to expose for as long a time as may be required 
 for a view, landscape, flowers, or inanimate objects, so as 
 to obtain, what ought to be the chief aim, extremely 
 fine detail in the picture ? In most cases, therefore, 
 although rapidity can be gained by enlarging the stop, 
 results will show it had better be avoided. With the 
 single lens just mentioned, a view, illuminated with the 
 sun, can be easily obtained in twenty to thirty seconds, 
 and if there be any persons in the view, they will without 
 doubt be copied. If, with the same single lens, an endea- 
 vour be made to take a portrait of a person placed in 
 the shade, it will require from three to five minutes. Is 
 it possible to remain so long without moving ? Certainly 
 not. Now the double lens will allow such a portrait to 
 be taken in ten seconds ; and although it gives a picture 
 not quite so sharp as the single lens, it nevertheless is 
 greatly preferable, and would in reality produce a sharper 
 picture, for with the single lens no one could remain per- 
 i'ectly immoveable during a sufficient time. 
 
 In certain cases it is also necessary to use a stop with 
 the double combination lens; but instead of a stop of 
 ^ to J inch for a lens of 3 inches diameter, one of from 
 I to 1J inch is all that is required. Fig. 54 shows such 
 
PHOTOGRAPHIC CAMERAS, LENSES, ETC. 4:7 
 
 a stop at H ; it is placed in the hood of the lens, and 
 is chiefly employed when a group of portraits is required 
 to be taken. For the purpose of more clearly compre- 
 hending the reason for the use of a diaphragm when taking 
 groups, &c., with a double or compound lens, it may be 
 remarked that, the more extended the space occupied by an 
 object, the more light will there be on the ground glass ; 
 but at the same time, with the double lens there loillbe less 
 sharpness. An intermediate course is therefore adopted ; 
 that is to say, a diaphragm is employed, whereby a loss 
 is incurred in the matter of exposure for the sake of 
 gaining sharpness and definition. 
 
 Generally speaking, a single lens gives so perfect a defini- 
 tion to the whole of the object, that the operation of obtain- 
 ing a good focus is extremely easy. It is not so, however, 
 with the double combination lens; therefore, as a rule, the 
 head of the sitter should be carefully focussed, and a little 
 of the details sacrificed, if necessary, to obtain this point. 
 
 Compound lenses are manufactured and sold for taking 
 pictures of a certain size ; this must be understood to 
 mean the utmost of their capabilities, and those photo- 
 graphers who may be desirous of obtaining first-class por- 
 traits should always employ a larger lens than is absolutely 
 required. The following is a list of compound lenses par- 
 ticularly adapted to produce the finest portraits of the 
 given dimensions : 
 
 Size of Picture. Diameter of Lens. Length of Focus. 
 
 Inches. Inches. Inches. 
 
 4J by 3J ... 2| ... 7 
 
 6i 4f ... 3J ... 9! 
 
 8J 6J ... 4 ... 11 
 
 10 8 ... 4J ... 15 
 
 A new form of lens has lately been constructed for 
 views, consisting of two lenses, which allows a great 
 degree of sharpness to be obtained with more flatness of 
 field than the ordinary single lens. They are termed 
 orthoscopic or caloscopic. In a special note (Note 8), will 
 be given a description of some of the principles of optics, 
 a proper understanding of which will render more clear 
 many of the foregoing details. 
 
 For taking " carte de visite pictures " the best size of 
 compound lens that can be employed is 2f inches in dia- 
 meter and 5-inch focus. 
 
4:3 PHOTOGRAPHIC PROCESSES. 
 
 CHAPTEE VIII. 
 
 ON THE GLASS ROOM IN WHICH THE SITTER IS PLACED, 
 AND THE RULES TO BE OBSERVED IN TAKING PORTRAITS 
 AND LANDSCAPES. 
 
 To take an artistic portrait, or to choose the most favour- 
 able point of view for a landscape, requires an artistic 
 taste not to be acquired by reading, but allied in its cha- 
 racter to a natural instinct, of which instruction only 
 develops the germ, while practice simply modifies and 
 perfects the details. The remarks on the subject-matter 
 of this chapter will therefore be of an essentially practical 
 nature. 
 
 The general detail and arrangement of an operating 
 room suitable for photographic purposes, is represented 
 in the cut on succeeding page. It should be in some 
 elevated position, either on the roof of the house or on a 
 platform specially erected for the purpose. The side next 
 the south should be entirely closed, whilst the other, 
 towards the north, is glazed. The sheets of glass em- 
 ployed should be of moderate thickness, as a protection 
 from storms of hail, &c., and as white as possible rather of 
 a bluish tint than approaching at all to a green or yellow 
 colour. It is of importance to attend to the colour of 
 the glass used for the operating room, for, should it be of 
 a green or yellow tint, a considerable amount of actinic 
 rays* are cut off, and the exposure necessary for a good 
 portrait is greatly augmented. 
 
 The glass rooms should be furnished with curtains 
 having cords attached to them, by means of which the 
 too energetic action of the light may be moderated, and 
 proper direction given to it. In the figure it will be 
 seen that three sets of squares are shown the upper one 
 (of ground glass), which is parallel with the floor or 
 ceiling ; the lower one, which replaces the wall ; and the 
 middle one, which is on the slope. 
 
 * Those rays of light which produce chemical action, and are found 
 at the blue and violet end of the spectrum. 
 
THE OPERATING ROOM. 
 
 49 
 
 If now, with the object of producing an artistic effect, 
 it be desired to inundate the front of the model or sitter 
 with light, the lower and middle set of curtains should be 
 more or less closed. If a lateral lighting be desired, the 
 curtains of the upper window should, on the contrary, be 
 
 closed. The good taste of the operator must, however, 
 guide him as to the best disposition of the light. 
 
 On the right of the engraving, Fig. 55, is represented 
 the shaft of a column, against which the model may lean ; 
 also a balustrade, with a landscape painted in distemper ; 
 
50 PHOTOGRAPHIC PROCESSES. 
 
 and near the middle a white marble chimney-piece of the 
 style of Louis XV. ; all of which accessories, or others of 
 a similar character, will be found to aid in imparting a 
 general appearance of elegance to the resulting picture. 
 
 The colour of the walls exercises a marked influence on 
 the result. They should not be painted either red, yellow, 
 or green, for these colours have a very weak photographic 
 action, and throwing around them, as they do, tints of 
 their own colour, tend to prolong very materially the time 
 of exposure. Violet and blue colours are preferable, but 
 as they produce whites in the print, and as a wall painted 
 either deep blue or violet produces a result exactly similar to 
 a white wall, they should not be used for the background, 
 or that portion behind the sitter. Bluish grey is a mixed 
 tint which, on the whole, yields the best results, and is 
 a colour with which the whole of the glass room may be 
 painted, except that, according to taste, some parts may 
 be more or less deep than others. 
 
 It will be found very convenient to have several move- 
 able backgrounds, each painted with a different depth 
 of colour, so as to be used according to the colour of the 
 dress, &c., of the sitter, and thus produce the most effec- 
 tive contrast. 
 
 Oil colour is very disagreeable on account of its reflec- 
 tion. It will be found best to employ a mixture of slaked 
 lime, litmus, and lamp-black with which the whole of the 
 room may be painted, simply varying the proportion of 
 black. The same colour will serve to paint the floor of 
 the room; but if a carpet be employed instead of paint, 
 it is equally important that it should be of a greyish 
 tint. 
 
 In reference to the best colour for dresses to be worn 
 by sitters, the same remarks apply as have been made re- 
 specting that of the glass room ; that is to say neutral 
 tints, analogous to grey, violet, and blue, come out well, 
 while red, yellow, and green, yield results of an oppo- 
 site character. By increasing the exposure, however, in 
 some cases, and diminishing it in others, the undue 
 predominance of any particular tint can be materially 
 diminished. 
 
 When one or more persons are to be taken, they should 
 be allowed, in the first place, to assume an easy, natural 
 
THE HEAD-REST. 
 
 51 
 
 position, and then, by placing behind each a head-rest, 
 in such a way as to retain them in the position chosen, 
 the required steadiness of the upper portion of the body 
 is secured. 
 
 It is not necessary that the sitter should press the head 
 too strongly against the head-rest, but on the contrary, it 
 should only lightly touch ; because too great a pressure 
 restrains the respiration, thus imparting to the sitter an 
 appearance of constraint and uneasiness. 
 
 There are two kinds of head-rests. One in iron, or of 
 iron and wood, is represented in Fig. 55. The lower 
 part consists of a tripod and tube of 
 brass weighing about 40 Ibs., which serves 
 to prevent vibration in the upper por- 
 tion, which is applied to the head. This 
 consists of an iron tube having one piece 
 forked, and capable of being adjusted and 
 fixed by a screw in any desired position. 
 
 These head-rests are made to stand on 
 the ground; but Fig. 56 shows one con- 
 structed so as to be attached to a chair. 
 
 This form of head -rest is generally made 
 of hard wood : e is a flat piece of wood, 
 to be adapted to the back of a chair ; two 
 clamping screws, //, are attached to it ; 
 i i a grooved board which comes behind 
 the chair. It may be easily raised and 
 depressed, and is fixed in any desired 
 position by turning the screws f f. b b, 
 a double -jointed piece for adapting to the 
 position of the head, and capable of being 
 fixed by means of the screws shown in 
 the figure. The whole of this piece may 
 be raised an<J lowered, and fixed at d. a 
 is a moveable forked piece, against which J 
 the sitter leans. It will be easily per- f 
 ceived that the back of the chair must 
 come between the pieces e and i i. _ 
 
 Figure 55 shows also the manner of Fiy 56 He ad-rest. 
 obtaining a focus, in connection with 
 which may be observed that too great an inclination 
 should never be given to the camera ; as a rule it is 
 D 2 
 
52 PHOTOGRAPHIC PROCESSES. 
 
 best to have the lens about the height of the chest. A 
 very slight inclination of the camera will then be suffi- 
 cient to get a correct image of the sitter from head 
 to foot. 
 
 In taking a portrait from a sitting position, it is best 
 to lower the camera-stand a little, and thus avoid too great 
 distortion. 
 
 The nearer the camera is brought to the sitter the 
 longer the exposure ; and inversely, the further the camera 
 is removed, the shorter the exposure. And it is in this 
 way that the time of exposure may be varied from one 
 second to three hundred. But as a general rule, in taking 
 a full-length figure in summer, the plate should be exposed 
 twenty seconds, while a sitting position will require thirty 
 seconds. In winter these times of exposure should be 
 increased one-half. 
 
 The following is a general summary of the operations 
 involved in taking a portrait. The direction and amount 
 of light are the first things which claim attention, then 
 the attitude of the sitter. Focussing is the next opera- 
 tion, during which the sitter should be requested to keep 
 still, though not maintaining perfect immobility. The 
 plate should now be prepared in the dark room, on re- 
 turning from which any alteration which may have taken 
 place in the pose of the sitter during the absence of the 
 operator is corrected, and efforts made, by cheerful con- 
 versation, to induce an agreeable expression. Then, 
 when everything seems in order and ready, a final and 
 rapid adjustment of the focus is made; the focussing- 
 glass is withdrawn and replaced by the camera-back, 
 containing the sensitive plate. The lens is now un- 
 covered and the plate exposed, the necessity of complete 
 stillness having been previously enjoined on the sitter, 
 explaining, however, at the same time, that he may 
 breathe in the ordinary way, and if necessary wink, but 
 not move his eyes from the spot where first directed. 
 The time of exposure having expired, the lens is covered 
 and the slide of the camera-back closed, and the develop- 
 ment proceeded with in the dark room. 
 
 With reference to the means to be employed to estimate 
 the time of exposure in seconds, it will be found best to 
 read the time from a good watch with a second-hand, 
 
RULES FOR TAKING VIEWS AND PORTRAITS. 53 
 
 though the same object may be attained by suspending 
 a leaden or wooden ball by means of a cord 39^- inches 
 long. If the pendulum so constructed be made to oscil- 
 late, it will be found to mark seconds of time with 
 sufficient accuracy. 
 
 It has been already mentioned in chapter seven, that 
 lenses of a different construction are necessary for land- 
 scapes from those which are used for portraits. For 
 views and architectural 'subjects a single achromatic lens 
 is sufficient, but for portraits a double combination is 
 necessary. It has also been stated that the form of 
 camera-stand, Fig. 46, and cameras, Figs. 47 -and 48, 
 are those most applicable for landscape photography. 
 
 The rules which can be given for taking views are 
 much more simple than those for portraits. In point of 
 fact, success depends mainly on the taste of the operator 
 in selecting the landscape which he desires to reproduce, 
 and the particular point of view from which it is seen. 
 The focussing is accomplished in the ordinary manner. 
 
 It is only necessary to add, that views are taken by 
 the wet as well as the dry collodion process. With the 
 latter all that is required is a grooved plate -box, con- 
 taining some prepared plates, a camera-stand, and a large 
 black cloth with which to cover the legs of the camera- 
 stand, when it becomes necessary to replace an exposed 
 plate by one which has not received the luminous impres- 
 sion. With the wet collodion process, a photographic 
 tent, or a light tent carriage, is indispensable ; and the 
 operator must also take with him all the paraphernalia 
 of dishes, baths, bottles, &c., which form the necessary 
 furniture of a dark room. 
 
 Notwithstanding these difficulties, the wet collodion 
 process is to be preferred for the reproduction of archi- 
 tectural subjects and landscapes near great cities. But 
 for a long voyage, the dry collodion process is certainly 
 the best. 
 
 In the wet collodion process, the nature of the result 
 (good or bad) is known at once on the ground ; while 
 with dry plates the character of the picture is not ascer- 
 tained until the development is effected, which almost 
 invariably takes pjace at a great distance from the locality 
 in which the view was taken. 
 
54: PHOTOGRAPHIC PROCESSES. 
 
 Iii large cities and flat countries it is very easy to have 
 a tent or light carriage of waterproof cloth, carried, or 
 drawn if need be, by a porter or guide an arrangement 
 which offers the advantage of allowing the operator to 
 stop wherever he pleases, and conduct the work with 
 great facility. 
 
 Generally, before taking views, a preliminary visit is 
 made, with the object of ascertaining the best points of 
 view, and on such occasions the iconometer, or view 
 
 meter, Fig. 57, is found 
 very convenient. It re- 
 quires to be expressly 
 constructed for each 
 focus of lens and size 
 of camera, and resem- 
 bles very much in ap- 
 pearance an opera-glass. 
 
 Fig. 57. Iconometer. V . * 
 
 It consists of a small 
 
 lens, a camera, of the shape of an opera-glass, and a square 
 focussing glass. By turning the lens towards the view it 
 is represented reversed on the ground glass ; and in this 
 way the operator can judge whether his large camera 
 will take in the whole or what portion of the required 
 view. 
 
 Instead of the iconometer with lens and ground glass, 
 a more simple one may be employed, which in many 
 respects, however, is similar to that indicated in Fig. 57. 
 The observation is made through the front opening, and 
 on the large circle behind (to the left in the figure) a 
 rectangle is described equal to that which is yielded by 
 the lens attached to the camera. It is then only neces- 
 sary to observe what objects are included in the field of 
 vision, in order to ascertain what will be reproduced on 
 the ground glass. The iconometer with lenses is, how- 
 ever, the most convenient for general use, as it affords an 
 opportunity of knowing whether in the case of taking an 
 architectural subject, for example, the operator is or is 
 not too close, for then the vertical lines incline towards 
 a point, like the furrows in a horizontal field. 
 
DEVELOPMENT OF THE IMAGE. 55 
 
 CHAPTER IX. 
 
 DEVELOPMENT OF THE LATENT IMAGE OBTAINED IN THE 
 CAMERA-OBSCURA. 
 
 As soon as the proper time has elapsed for exposure, the 
 sensitised plate must be withdrawn from the light by 
 closing the shatter of the camera-back, which is then 
 taken into the dark room. After carefully closing the 
 shutter in front of the yellow -glass window, the plate is 
 removed from the frame. If it be now examined, there 
 will very rarely be any traces of a picture ; it can, how- 
 ever, be made apparent by covering the surface which 
 has been exposed to the light with a solution of some 
 substance capable of reducing the salts of silver to the 
 metallic state. 
 
 Among the reducing agents which can be employed in 
 photography, may be mentioned protonitrate of iron, 
 sulphate of iron, pyrogallic acid, protosulphate of uranium, 
 protosalts of osmium and titanium, (fee. ; but of all these, 
 pyrogallic acid will be found the best for developing the 
 negatives, and protosulphate of iron for obtaining direct 
 positives on glass. 
 
 Pyrogallic acid is a white crystalline solid, without 
 smell.* It is soluble in water, alcohol, and ether, and 
 its solution in either of these menstrua becomes rapidly 
 decomposed on exposure to the air and light, especially 
 if the solution be alkaline. This substance alters very 
 soon even when it is dry. If a small amount of moisture 
 be present, however, the decomposition proceeds with 
 increased rapidity, being expedited by the foreign matter 
 which it contains. Thus it is better -first, to keep 
 the pyrogallic acid bought in shops in small stoppered 
 bottles ; secondly, to keep it in the dark ; thirdly, never 
 to prepare with it more developing solution than is likely 
 to suffice for a day's consumption.. 
 
 It is usual to add to the pyrogallic some other acid, as 
 
 * For its method of preparation see Note 7 
 
OO PHOTOGRAPHIC PROCESSES. 
 
 much to preserve the solution as to develop the picture 
 uniformly ; distilled water also must be employed, or at 
 least rain-water, well filtered : that which is obtained 
 during a storm contains ammonia or nitric acid, and is 
 therefore unfit for use. 
 
 Solution of pyrogallic acid for developing, is thus pre- 
 pared : A flask of about 1 pint capacity is obtained, and 
 made perfectly clean ; to this is adapted a funnel, fur- 
 nished with a filter, as shown in Fig. 11. Upon this filter 
 throw 15 grs. of pyrogallic acid ; then 15 ozs. of distilled 
 water being measured off, and 1 oz. of crystallisable acetic 
 acid* being added thereto, the whole is well stirred with 
 a glass rod, and poured on to the filter containing the 
 pyrogallic acid, which latter dissolves as the liquid is 
 passing through. The filtration being complete the funnel 
 is removed, and the flask stopped lightly with a cork, and 
 set aside for use in the dark. 
 
 MM. Davanne and Girard have proposed the substi- 
 tution of citric for the acetic acid, in which case the 
 following formula may be employed : 
 
 Distilled Water 12 fluid ounces. 
 
 Pyrogallic Acid 15 grains. 
 
 Citric Acid 15 
 
 "Whichever formula is adopted, the method to be followed 
 to develop the picture is precisely the same ; and it is 
 important to note that the development should take place 
 as soon as possible after the plate is sensitised, and on no 
 account should a longer time than five minutes be allowed 
 to elapse between these operations. 
 
 The plate, on removal from the frame, is held by one 
 corner (the same by which it was held when 
 the collodion was poured over it) ; then 
 a sufficient quantity of the developing solu- 
 tion to cover the plate being placed in a 
 glass (Fig. 58), is poured by a continuous 
 operation over the collodion surface, and the 
 plate inclined alternately in every direc- 
 Ftg ' 58 ' tion,-in order that the whole film may be 
 covered without delay. Then suddenly turn the plate up- 
 
 * See Note 11. 
 
DEVELOPMENT OF THE IMAGE. Of 
 
 right, holding it by the opposite corner to that from 
 whence the liquid flows into the glass. 
 
 Fig. 59. Developing a Negative Proof. 
 
 The same solution is again poured on the plate, inclin- 
 ing it constantly from right to left, in order that the liquid 
 may be kept in continual motion. The 
 image gradually appears ; and when it is 
 considered sufficiently developed, the plate 
 is washed by dipping it, at first very care- 
 fully, into a shallow porcelain tray, filled 
 with water ; it is then placed under a small 
 stream of water, after which it is fixed. 
 It is desirable, for washing the plate, to 
 use a little apparatus represented in 
 Fig. 60. It is simply a flask, filled with 
 distilled water. The cork is perforated, 
 so as to admit of the passage of two tubes. Fi[ 
 The highest that which is to be blown through passes 
 D 3 
 
58 
 
 PHOTOGRAPHIC PROCESSES. 
 
 through the cork, and terminates directly under it ; the 
 other, on the contrary, rests in the water at the bottom of 
 the bottle. The draughtsman has reversed this arrange- 
 ment in the figure by mistake. 
 
 In using this wash-bottle, it is held by the neck while the 
 
 operator blows through 
 the higher tube, by which 
 means the water is pro- 
 jected through the exit 
 tube, and may be directed 
 over the surface of the 
 film, beginning at the 
 centre, and passing gradu- 
 ally to the edges, thus 
 avoiding disruption. Fig. 
 61 shows the operation 
 better than any verbal 
 description. 
 
 In order to avoid taking 
 the plate in the hand, an 
 India-rubber plate-holder 
 is sometimes employed 
 with advantage. Fig. 62 
 shows a glass plate at- 
 tached to such a plate - 
 
 i. washing the Film. holder. To do this the 
 
 plate is placed on a level table, arid the holder grasped 
 by the globe part in such a way as to force out the air ; 
 the edges are then moistened, in order to make them 
 adhere more perfectly, and the pressure is withdrawn at 
 
 the moment of bringing 
 the plate-holder in con- 
 tact with the glass by 
 pressing the edges of it. 
 Although the air has 
 been forced out of the 
 bottle, its elastic sides 
 re -assume their shape, 
 and the vacuum left in- 
 side causes the plate to 
 Fig. 62. Pneumatic Plate-holder. adhere very firmly to 
 
 the plate -holder. To detach it, it is only necessary to 
 
DEVELOPMENT OF THE IMAGE. 59 
 
 compress the bottle as before. The picture having been 
 developed and washed, is now fixed, an operation to be 
 described in the next chapter. 
 
 The process of developing the picture, although appa- 
 rently simple, is, nevertheless, a very delicate one, and 
 one on which depends, in great measure, the success of 
 the positive proof; it will not, therefore, be out of place to 
 enter a little more into detail. The latent image produced 
 by the action of light upon the iodide of silver, is brought 
 out by the action of pyrogallic acid, aided by the nitrate 
 of silver, with which the collodion film is impregnated. 
 If too much pyrogallic developing solution is poured from 
 the developing glass on to the plate, the details of the 
 picture appear but slowly, and if too little there will not 
 be enough to cover the plate completely ; thus the medium 
 lies between the two extremes. 
 
 Sufficient developing solution should be poured into 
 the glasb to cover the plate freely and completely, and no 
 more ; and this should be poured on and off, and allowed 
 to flow in various directions, in order to facilitate the 
 mixture of the developer with the adherent nitrate of 
 silver. By this method of manipulating it will be found 
 that the development proceeds uniformly, and may be 
 observed from time to time by examining the plate by 
 transmitted light, as indicated in Fig. 59. 
 
 The development is continued according to the pre- 
 ceding directions until the required amount of intensity is 
 obtained, and the plate is then rinsed with water to remove 
 the developing fluid, so as to prevent its continued action. 
 
 At an ordinary temperature the picture is generally 
 sufficiently developed in two minutes ; but if it is necessary 
 to force the development, it will seldom prove a successful 
 picture. At a higher temperature it sometimes becomes 
 necessary to stop the development in half a minute, to pre- 
 vent the high lights from becoming too dense. Experience 
 alone can give the knowledge necessary to determine 
 exactly the when and how in this delicate operation. 
 
 As soon as the solution of pyrogallic acid covers the 
 plate, the sky and the high lights of the picture begin to 
 appear on the primrose-tinted film of iodide of silver ; a 
 few seconds after, the minor details make their appearance, 
 becoming more and more vigorous, and, as often occurs 
 
60 PHOTOGRAPHIC PROCESSES. 
 
 in a landscape, the sky darkens so much, that it is even 
 difficult to see the sun through it. This will give an idea 
 of the amount of intensity which the image acquires ; and, 
 without experience, it is very difficult to indicate the 
 exact moment when the pyrogallic acid should be removed 
 by treatment with cold water. 
 
 The quantity of acetic acid added to the pyrogallic 
 also exercises an important influence on the results, and 
 in proportion as it is increased the more slowly the image 
 appears, and the more vigorous it is in character. When, 
 for example, a negative has to be developed taken from 
 
 Fig. 63. Positive Proof. From a Stereoscopic View by Ai. j 
 
 a group of persons among whom there are some having 
 on white dresses, a large proportion of acetic acid is 
 necessary; while, on the contrary, a dull, grey, sombre 
 monument develops best with a small proportion of acetic 
 acid. The time and character of the development of a 
 picture also enables a conclusion to be arrived at, as to 
 whether the exposure in the camera has been too long or 
 too short. 
 
DEVELOPMENT OF NEGATIVES. 61 
 
 In this latter case it is with difficulty that the sky and 
 the other high lights of the picture are developed, and 
 detail in the shadows is never obtained ; even after long 
 waiting the image will not appear, in which case it is 
 necessary to take a fresh negative. 
 
 Fig. 64. Negative Proof, examined on the Side of the Glass not covered 
 with Collodion. 
 
 If, on the contrary, the exposure has been too long, the 
 negative is red and uniform ; after fixing, there is an 
 absence of vigour in the blacks, and there is a general 
 fogging spread over every part of the image ; the develop- 
 ment also ,has taken place very rapidly. In each case 
 another negative must be taken. 
 
 The most frequent error is over-exposure, arising from 
 an inability to realise the possibility of taking a picture 
 in so short a time. 
 
 For the purpose of illustration, suppose the monument 
 represented at Fig. 63, representing a portion of the 
 Acropolis at Athens, is to be reproduced. 
 
 The sun illuminates these statues with all its meridian 
 
62 PHOTOGRAPHIC PROCESSES. 
 
 splendour; strong shadows are therefore a necessary con- 
 sequence, which, in order to be correct, ought to be in 
 the negative. 
 
 Beginning with a negative which shall not have been 
 exposed in the camera more than five seconds, and suc- 
 cessively increasing the time of exposure, five seconds in 
 a series of five negatives, the following will be the 
 result : 
 
 The first negative will be very slow in developing ; 
 after several minutes the sky will with difficulty be traced, 
 and some faint indication may be obtained of the parts 
 most strongly lighted. 
 
 In the second these portions will have acquired much 
 more vigour, and the shadows even will begin to yield 
 some indication of detail. The third negative will be a 
 good one ; but the fourth will be, in every respect, all 
 that could be desired, possessing a due amount of vigour, 
 and presenting the aspect of Fig. 64. 
 
 The fifth negative, although exposed a longer time, 
 will have acquired a greyish colour. A good negative is 
 blue ; but too long an exposure gives it a dull grey ap- 
 pearance. The shadows, instead of being transparent, 
 like glass itself, have upon them a sensible deposit, owing 
 to the too rapid development. 
 
 In proportion as the exposure is increased in any sub- 
 sequent negative, the grey colour tends to become red ; 
 there is a difficulty almost in distinguishing the shadows 
 and the sky ; and, in one word, the negative loses all its 
 vigour. 
 
 The above are the principles upon which the photo- 
 grapher should proceed in the correction of his negatives. 
 
 It would be useless to pretend that an accurate judg- 
 ment can be formed except by long experience. It is not 
 until after several months of assiduous research, and after 
 continual disappointment, that the beginner will acquire 
 that accuracy of judgment at a glance which will guide 
 him in the fugitive indications of the amount of exposure 
 necessary for a given subject ; but, when once this know- 
 ledge is acquired, he will be amply rewarded by the 
 small number of defective negatives, as well as by the 
 amount of photographic knowledge acquired during the 
 apprenticeship. 
 
SPOTS AND MARKINGS. 
 
 63 
 
 It frequently happens that negatives are spotted, or 
 
 covered with curious markings, either in parts or entirely. 
 
 The four accompanying figures are some examples of 
 
 Fig. 68. 
 
 these spots, taken from M. de la Blanchere's work ; the 
 description of them, together with practical directions for 
 their avoidance, will be found in Note 9 at the end of 
 the volume. 
 
64: PHOTOGRAPHIC PROCESSES. 
 
 CHAPTER X. 
 
 FIXING AND STRENGTHENING THE NEGATIVE IMAGE. 
 
 IT has been before stated that when the image is suffi- 
 ciently developed, the plate should be washed with 
 water, so that the pyrogallic acid may be well removed. 
 Should the film show any tendency to detach itself, this 
 operation must be performed with considerable care. The 
 email shutters may now be opened, so as to uncover the 
 whole of the yellow windows. The light in the dark 
 room is thus increased, although it still retains its yellow 
 tint. 
 
 The result thus obtained is a negative image, but still 
 partly obscured with iodide of silver, which is now to be 
 removed. For this purpose it must be plunged into a bath 
 composed as follows : 
 
 Water 40 ounces. 
 
 Hyposulphite of Soda 8 ounces. 
 
 In about half a minute, if the bath is fresh, and some few 
 minutes if the bath has been much used, all the yellow 
 coating of iodide of silver is dissolved, and there remains 
 on the collodion film only the pure silver compound con- 
 stituting the photographic image. 
 
 Hyposulphite of soda is a crystallised substance, very 
 soluble in water 4 , and can be purchased at a very cheap 
 price. 
 
 The. solution of hyposulphite of soda may be contained 
 in a vessel of zinc or gutta-percha. It does not stain the 
 hands ; on the contrary, it will remove recent stains of 
 nitrate of silver. 
 
 Great care should be taken that the vessel containing 
 the bath of hyposulphite be kept separate, and that the 
 fingers be well washed before proceeding to take another 
 picture, because contact with this salt spoils both the 
 collodion and nitrate of silver bath. 
 
 In fixing the proof, it should not be allowed to remain 
 
FIXING AND STRENGTHENING THE NEGATIVE. 65 
 
 too long in the bath of hyposulphite, otherwise the fine 
 details will be injured. The entire solution of the iodide 
 of silver is easily perceivexl by examining the back of the 
 glass. The iodide of silver being of a pale yellow colour 
 is easily seen, and it is, however, necessary that the last 
 traces of this colour be allowed to disappear. When this 
 result is obtained, the glass plate should be taken out and 
 plunged into a bath of cold water. 
 
 The solution of hyposulphite will serve a considerable 
 time before it is exhausted, and then it is of so little cost 
 that a fresh solution is easily made. 
 
 When the negative proof is immersed in the hyposul- 
 phite, the vessel containing it may be taken to the day- 
 light, which will enable the operator better to see when 
 the yellow coating of iodide of silver is quite removed. 
 Ordinary daylight from this time has no action on the 
 picture. 
 
 After the fixing is complete, it is of the greatest 
 importance thoroughly to wash the collodion surface, 
 especially if a great number of proofs are to be printed 
 from it; this becomes more difficult when the coating has 
 a great tendency to detach itself from the edges of the 
 glass. Nevertheless, even under these circumstances, 
 with a little attention it may be perfectly washed. When 
 the collodion is good, and especially if the gun-cotton 
 has been prepared according to the formula indicated 
 in Note 3, there will not be the least fear of such an 
 accident. 
 
 When the film appears liable to detach itself, the small 
 apparatus, Fig. 60, which has already been described, is 
 made use of. The current of water is carefully directed 
 from the middle of the plate towards the edges, constantly 
 varying the inclination in such a way that the water 
 always flows from the centre towards the sides. By these 
 means the coating is prevented, as far as practicable, from 
 being totally removed. Care must also be taken when 
 the glass is left to drain, as the coating wrinkles and 
 bends by its own weight. This effect shows itself while 
 the coating is yet quite wet. When the excess of water 
 lias disappeared, a little care will enable the coating to be 
 drawn to its proper position by the aid of the finger. 
 
 To properly wash the coating the glass should be 
 
66 PHOTOGRAPHIC PROCESSES. 
 
 placed, during five minutes at the least, in a large vessel 
 of zinc filled with water. If the coating separates in any 
 part the glass must be very gently removed, and the 
 detached parts arranged and brought together by a 
 very fine and light jet of water applied to the required 
 places. We have often in this way replaced a film upon 
 the glass after it has been entirely removed and torn at 
 the edges, and in spite of all obtained good results. 
 
 If the glass be not sufficiently washed after removal 
 from the hyposulphite, the film becomes sticky, and after 
 awhile disappears altogether, or, at least, becomes strongly 
 stained. 
 
 It is after removal from the hyposulphite of soda that 
 the proof can be best examined as to its quality. It ought 
 to be of a bluish colour ; the sky and high lights a strong 
 black, and the deep shades nearly transparent. 
 
 If at this moment a good photographer judges that his 
 negative is wanting in vigour, he commences another; 
 but if this is impracticable, recourse must be had to inten- 
 sify ing. This operation must be done after the proof is 
 fixed and washed, and before it is dried. 
 
 Generally speaking, an intensified negative is worth 
 but little ; and, to repeat, a good operator will rather re- 
 commence another negative than intensify. However, if 
 required, the best method is as follows : 
 
 The glass plate, after the rinsing which follows the 
 fixing, is plunged into a porcelain vessel containing a 
 solution of bichloride of mercury in water. 
 
 Water 10 ounces. 
 
 Bichloride of Mercury to saturation. 
 
 (To saturate the water with bichloride of mercury, this 
 Bait, after being powdered, is introduced into a bottle 
 filled with water, and well agitated.) 
 
 In a few minutes the coating assumes a milky-white 
 appearance. The plate is now removed and washed with 
 the greatest care, and then plunged into a solution of 
 
 Water 10 ounces, 
 
 Liq. Ammonia 1 ounce; 
 
 when it immediately becomes darkened. On being taken 
 from this bath the plate is washed with water, and then 
 placed against the wall to drain and dry. 
 
VARNISHING THE PICTURE. 
 
 67 
 
 The best method of drying glass plates consists in 
 placing them (Fig. 69) resting 
 by their upper edge against the 
 wall, and their lower edge upon 
 a sheet of bibulous paper, which 
 very quickly absorbs the excess 
 of water. 
 
 If the plate is required to be 
 quickly dried, the coated sur- 
 face ought to be from the wall ; 
 and, on the contrary, if it is re- 
 quired to be slowly dried, the 
 coated surface is placed towards 
 the wall. In this latter case, 
 the particles of dust do not so 
 readily attach themselves to the 
 surface of the picture. 
 
 The intensifying which we have described is very 
 powerful ; but it is capable of being regulated, by leaving 
 the plate, for a few seconds only, in the bath of bichloride 
 of mercury. The less time the plate is in the solution, 
 the smaller the quantity of ammonia required to darken 
 it. After a few years, a proof intensified by this method 
 loses its vigour, and becomes even more feeble than it 
 was before. Several other methods for intensifying have 
 been proposed in various photographic works ; none of 
 them, however, can be recommended in preference to 
 that described. At the same time, if a good proof be not 
 obtained at the first attempt, by far the better plan will 
 be to try again, as it is by this means alone that real 
 perfection can be attained in the photographic art. 
 
 Fig. 69. 
 
 CHAPTER XI. 
 
 VARNISHING THE PICTURE. 
 
 WHEN the proof is fixed, washed, and dried, its surface 
 exhibits by reflected light a fine metallic appearance ; if 
 the development has been carried too far, the coating 
 
bS PHOTOGRAPHIC PROCESSES. 
 
 appears covered with a metallic dust, which, however, 
 can be partially removed with the aid of a very soft 
 brnsli. By transmitted light the picture has an entirely 
 different appearance, perfectly opposite to that exhibited 
 by reflection. 
 
 As a collodion negative is required to furnish a consi- 
 derable number of positive proofs upon paper, and for 
 which purpose the collodion surface requires to be placed 
 in contact with the sensitive paper, it becomes necessary 
 to protect this coating by a sufficiently hard varnish, so 
 that the plate can be easily handled without risk ; other- 
 wise the soft coating would be very liable to injury. 
 
 There are two excellent varnishes suitable for the pur- 
 pose amber varnish, and the white gum, or Soelinee 
 varnish. 
 
 The amber varnish is thus prepared. A quantity of 
 yellow amber, broken into small pieces, is placed in a 
 bottle so as to occupy about three -fourths of its capacity. 
 A mixture of equal parts of chloroform and ether is now 
 poured into the bottle, in such a quantity that the amber 
 is hardly covered. After some few days the liquid con- 
 tents of the bottle are poured upon a filter, and the pale 
 yellow liquid which passes through is amber varnish. 
 
 The solid fragments of amber are allowed to remain 
 in the bottle, to which can be again added the mixture of 
 chloroform and ether, and a fresh quantity of varnish 
 obtained. The same amber will serve for a dozen or 
 more times, if care be taken to keep the bottle well closed. 
 
 To prepare the gum -lac, or Soehnee varnish, place in a 
 bottle 
 
 Gum-lac White * 21 ounces. 
 
 Alcohol 35 ounces. 
 
 The bottle* is now well stopped and left several days, 
 being well agitated at frequent intervals ; the liquid is 
 then left to settle as much as possible, the clear portion 
 poured off, and the remainder filtered. The whole of 
 the liquid can be filtered ; but it is not recommended, as 
 it passes very slowly through the paper. The colour of 
 this varnish is of a pale yellow, less deep than the 
 chloroform. 
 
 Instead of making this preparation in a bottle at the 
 ordinary temperature, it will be found a more expeditious 
 
VARNISHING THE PICTURE. 69 
 
 plan to employ a flask (containing the materials), placed 
 in hot water. If the flask, thus kept heated, he agitated 
 from time to time, the gnm-lac can be dissolved in about 
 half an hour. There is always a whitish deposit, which 
 does not dissolve either in cold or hot alcohol ; this must 
 be allowed to perfectly settle before the varnish is poured 
 off for use. 
 
 The amber varnish is very easily applied ; the collodion 
 surface of the plate, on which the picture is formed, is 
 covered with it in the same way as the collodion was 
 applied, the excess of liquid being received in the bottle. 
 In a few seconds this varnish is dry. It is well, however, 
 to expose the plate for an, hour to the sun before being 
 used for printing from. 
 
 It is more difficult to make use of the white gum-lac 
 varnish, because the plate then requires to be warmed. 
 For this purpose it is carefully exposed to the flame of a 
 spirit lamp, or before a clear fire, taking care that the 
 heat is equally applied by moving about the glass plate 
 at some distance from the fire, or above the flame, if this 
 be employed. 
 
 The temperature of the glass should be such that, 
 when applied to the back of the hand, it can i>e borne 
 without inconvenience. If too hot, the varnish flows 
 with difficulty over the surface; and if too cold, it does 
 not dry sufficiently quick, and becomes chilled or partially 
 opaque. This varnish is applied like collodion, the 
 excess being received in the bottle, and when the surface 
 appears dry, the heat is continued a short time longer, so 
 as to cause a proper transparency and adhesion of the 
 coating. 
 
 It is especially difficult to use the gum-lac varnish for 
 plates of large size, for which, all things considered, it 
 is generally best to employ the amber varnish. The 
 negatives are less firmly varnished, and, in consequence, 
 not able to yield so large a number of proofs ; but, on the 
 other hand, it is much more easily applied. 
 
 It constantly happens that a number of transparent 
 round spots appear on the negative, which require stop- 
 ping out before the positive proofs are obtained from it, 
 otherwise these white spots would form corresponding 
 black ones on the prints, which cannot be removed. If, 
 
70 PHOTOGRAPHIC PROCESSES. 
 
 on the contrary, the spots on the negative be black or 
 opaque, white spots are formed on the positive proof, 
 which are comparatively easy to be touched out by a 
 little water colour. 
 
 Touching out a negative requires very careful manipu- 
 lation, and a properly arranged apparatus for the purpose 
 will be found very convenient, Fig. 70. The wooden top 
 
 Fig. 70. Apparatus for touching out Glass Proofs. 
 
 of a small table is removed, and a thick sheet of glass, 
 supported by an iron framing, is substituted. Below is 
 arranged a large sheet of white paper, stretched upon a 
 frame, or else a looking-glass, of which the inclination 
 can be varied by some such contrivance as shown in the 
 figure. 
 
 The light reflected from the looking-glass or paper, 
 enables the proof, which is laid on the glass -plate form- 
 ing the top of the table, to be conveniently examined by 
 transmitted light. 
 
 The transparent spots are then touched out with a very 
 fine camel's hair pencil, and some dark colour mixed with 
 
THE DRY COLLODION PROCESS. 71 
 
 honey or oil.* Some persons touch out the spots with 
 Indian ink, mixed with a small quantity of Prussian blue, 
 before the plate is varnished. This plan, however, cannot 
 be recommended, as the subsequent varnishing is apt to 
 destroy the colour applied. 
 
 Light spots on paper proofs are easier to touch 
 out with water colour of the same tint as the print, 
 than glass negatives are : therefore, whenever circum- 
 stances allow a choice to be made, preference should be 
 given to the former. For example, if there should be a 
 white spot on the negative, with which nothing can be 
 done, it will be better to make it a black one, which, by 
 printing white on the paper proof, can be then easily 
 tinted of the proper colour. 
 
 CHAPTER XII. 
 
 THE DRY COLLODION, COLLODIO-ALBUMEN, AND TANNIN 
 PROCESSES. 
 
 1. The Dry Collodion Process. 
 
 ONE of the most unfortunate circumstances connected 
 with the practice of photography on wet collodion, is the 
 necessity, in travelling, for the photographer to employ 
 a tent, which adds greatly to his luggage. This incon- 
 venience is due to the fact that the operations of sensi- 
 tising and developing must quickly follow each other, for, 
 if too long a time elapses between them, the nitrate of 
 silver crystallises on the surface of the glass, and causes 
 an infinite number of small spots to be formed over the 
 entire surface of the picture. 
 
 If the glass plate, covered with its sensitised coating 
 
 * M. de la Blanchere gives the following formula : 
 
 Peroxide of Iron, or Rouge ; Chromate of Lead, 
 
 or Ivory Black 10 parts. 
 
 Gum Arabic, Saturated Solution 2 
 
 White Honey 2 
 
 Sugar Candy 1 part 
 
72 PHOTOGRAPHIC PROCESSES. 
 
 of collodion, be washed with distilled water when re- 
 moved from the silver-bath, and left to dry, it loses 
 nearly all its sensibility, and will give but very imperfect 
 pictures. 
 
 M. Desprats and M. Dubosq have partially remedied 
 this fault : the former, by adding half per cent, of 
 resin; the latter, some few drops of amber varnish to the 
 collodion ; in whichever of the two methods it is pre- 
 pared, it must be used exactly as ordinary collodion, 
 with the exception that when the glass is removed from 
 the silver-bath, it is to be well washed and dried in the 
 dark. Plates thus prepared will preserve their sensibility 
 for many days. The time of exposure in the camera 
 ought to be tripled, and the development made with solu- 
 tion of gallic acid. 
 
 M. Dupuis recommends the adoption of the following 
 process. Ordinary iodised collodion is employed, and the 
 glass plate after being sensitised, is well washed in distilled 
 water. A solution of dextrine, in ten times its weight of 
 water, is left to settle, and then decanted, so as to be free 
 from impurities. A requisite quantity of this solution is 
 poured over the sensitised glass plate, recently washed, 
 and while still moist, in such a manner, that it spreads 
 evenly over its surface ; it is then drained and dried. 
 
 The plates thus prepared will keep good for several 
 days ; but the time of exposure in the camera must be 
 tripled, that is to say, if with wet collodion, 30 seconds of 
 exposure is required, it will be requisite to give 90 with 
 a plate prepared with dextrine. 
 
 Before developing the plate, it is washed with pure 
 water. An apparatus, consisting of a flat-bottomed 
 flask, &c., similar to that described page 57, is useful 
 for this purpose. The picture is developed with pyro- 
 gallic acid. 
 
 A great number of other dry processes have been pro- 
 posed ; but two, above all others, have obtained the prefer- 
 ence of the photographic public, as well in England as in 
 France and Germany, these are the collodio albumen 
 process of M. Taupenot, and the tannin process of 
 Major Russel. These two processes will, therefore, be 
 described in all their details. 
 
THE COLLODIO-ALBUMEN PROCESS. 73 
 
 2 The C ollodio-albumen Process. 
 
 As by this process a considerable number of plates can 
 be prepared in a few hours, which is very convenient, 
 especially for obtaining stereoscopic positive proofs upon 
 glass, which will presently be described. The following 
 will be found an excellent method, and one which will 
 enable a hundred of these plates to be properly pre- 
 pared, in two operations of four hours' continuous work, 
 it being understood that the glasses do not exceed the 
 dimensions of 9 inches by 7 inches, and that they are all 
 cleaned beforehand. 
 
 In the dark room are arranged two vessels of gutta- 
 percha, one beside the other, both containing a silver-bath 
 composed of 
 
 Water 35 ounces. 
 
 Fused Nitrate of Silver 1050 grs. 
 
 One bath only may be employed, but with two the opera- 
 tion, as will be perceived, is much quicker. 
 
 Ordinary negative collodion may be used, but it will 
 be found an improvement if the collodion is a little less 
 iodised, such as is obtained by adding to the ordinary 
 collodion of which the formulae has been given at page 22 
 one third of its volume of a mixture of about two parts 
 of ether and one of alcohol. 
 
 Collodion, ordinary, (page 22) 3 ounces. 
 
 Ether, 5 fluid drs. \ , __ 
 
 Alcohol, 3 do / ' -1 ounce. 
 
 For the purpose of facilitating the description, the 
 glass plates will be designated by the letters A, B, C, and 
 the nitrate of silver baths by numbers 1 and 2. 
 
 A glass, A, is coated with collodion and plunged into 
 the first silver-bath (No. 1). A second glass is now 
 coated with collodion, and plunged into the second bath 
 (No. 2). 
 
 By the side of the silver-baths should be placed a 
 vessel of gutta-percha of considerable depth, and filled 
 with filtered rain-water, or better, with distilled water. 
 This bath ought to be as capacious as possible. 
 
 When the first glass, A, has been a sufficient time in 
 the silver-bath, No. 1, which is ascertained by the dis- 
 
 E 
 
74: PHOTOGRAPHIC PROCESSES. 
 
 appearance of the greasy veins which have been spoken 
 of at page 35, it is taken out and placed in the bath of 
 water contained in the vessel of gutta-percha. 
 
 A third glass, 0, is then coated with collodion and 
 plunged into the silver-bath, No. 1, from which the first 
 glass was taken, and then the glass in the bath of water 
 is removed, and placed in a large wooden tub (Fig. 71) 
 tilled with rain-water, and sufficiently large to hold from 
 eight to ten glasses, placed side by side. 
 
 Fig. 71. Tub for Washing Plates. 
 
 The second glass, B, is now taken from the silver-bath 
 and plunged into the bath of water in the gutta-percha 
 vessel. It is left here while another glass is coated with 
 collodion and sensitised, and when that is finished the 
 second glass, B, is taken from the water, to be placed in 
 that contained in the large vessel Fig. 71. The plate, C, 
 is removed to the bath of water, a fresh plate inserted, 
 and the same series of operations repeated for the number 
 of prepared plates required. 
 
 It will be understood that this method of preparation 
 being a continuous one, is necessarily very rapid. When 
 the large vessel of water is filled with plates, they are to 
 be taken out and placed inclined against the wall, resting 
 at the bottom on some bibulous paper, and with their 
 prepared or collodionised surfaces towards the wall, as 
 described at page 67. 
 
 If the operation be conducted on a small scale, with 
 one glass at a time, then, when the first plate is taken 
 from the silver-bath and plunged into the water-bath, 
 another plate is coated with collodion and placed in the 
 nitrate -bath, and during the time it has to remain in it, 
 
THE COLLODIO-ALBUMEN PROCESS. 
 
 75 
 
 the first plate is removed to a fresh quantity of water 
 contained in a trough of wood or gutta-percha. 
 
 Whichever method be employed, the result will be the 
 same, provided that care be taken to remove the whole 
 of the nitrate of silver, which covers the plates, with 
 abundance of water ; if the trough be small, the water 
 must be often changed; but if it be of large size, this 
 may be dispensed with. 
 
 When the whole of the plates are prepared, some 
 solution of common salt is added to the water contained 
 in the gutta-percha trough. 
 
 A white precipitate is formed of chloride of silver, 
 which can be retained until of sufficient quantity, 
 with other residuums, to be reduced into metallic 
 silver by fusion in an earthen crucible with carbonate of 
 soda. 
 
 Each glass plate should remain in the water at least 
 ten minutes, and ought to be kept upright, the better 
 to remove all the soluble salt of silver from the texture 
 of the collodion coating. 
 
 The glasses, coated with collodion and washed as just 
 described, must be covered while still 
 moist, with iodised albumen, which is 
 thus prepared: 
 
 Fresh fowls' eggs are broken 
 across the middle, the whites care- 
 fully separated, and then poured into 
 a glazed earthen vessel, to which is 
 added a quantity of iodide of potas- 
 sium, equal to 7 J grains to the white 
 of each egg employed. Before adding 
 the iodide of potassium to the white 
 of egg, it should be dissolved in an 
 equal weighjb of water ; for example, 
 if ten, twenty, or fifty eggs be used, 
 75, 150, or 375 grains of iodide of 
 potassium are required, dissolved in 
 75, 150, or 375 grains of water. 
 
 The whole is then beaten completely into froth by 
 
 means of a bundle of twigs, represented at Fig. 72, or of 
 
 tinned iron wire, mounted in a handle, Fig. 73. This 
 
 froth is left to itself in a glazed earthen vessel, Fig. 74:, 
 
 E 2 
 
 Fig. 72. Fig. 73. 
 
76 PHOTOGRAPHIC PROCESSES. 
 
 for twelve hours, when the greater portion is resolved 
 into clear albumen, which can be poured off into a wide- 
 mouthed bottle. This iodised albumen is used to pour 
 over the collodionised glasses after they have been taken 
 from the trough, Fig. 71, and drained for one or two 
 minutes on a wooden shelf, Fig. 69. 
 
 Fig. 74. Albumen beaten into Froth. 
 
 M. Taupenot employed fermented albumen ; but it is 
 now not generally used or to be recommended. 
 
 Iodised albumen can be preserved for a considerable 
 time during winter, but in summer it is apt to decompose 
 very rapidly. It should be kept in well-closed bottles 
 in a cool place. 
 
 During the time that some of the glasses require to 
 remain in the silver-bath, those which have been drain- 
 ing against the wall are to have a small quantity of the 
 albumen poured on each, and allowed to run over every 
 portion of the moist collodion surface ; the glass is then 
 held vertically, so as to allow the excess of liquid to flow 
 into a separate bottle, which, for the sake of distinction, 
 will be called B. 
 
 A fresh quantity of the iodised albumen is now 
 poured on the glass, and made to flow over every portion 
 of its surface, the excess being received back into the 
 bottle. 
 
 The glasses thus albumenised are left to dry, the 
 upper part of each leaning against the wall, and the 
 lower resting on some blotting-paper, as shown at Fig. 69.^ 
 
THE COLLODIO-ALBUMEN PROCESS. 77 
 
 The albumenised surface should be towards the wall, to 
 avoid dust. 
 
 The reason for giving the plates two coatings of 
 albumen is that the tirst application serves to remove the 
 water which impregnates the collodion surface and allows 
 the second quantity to give a perfectly uniform coating. 
 The albumen contained in the bottle, B, can be used a 
 considerable number of times for giving the first coating 
 or until it becomes too diluted with the water derived 
 from the plates, when a fresh quantity must be used ; 
 whereas, that employed for the second coating, on the 
 contrary, can be used as often as required. 
 
 The glasses, when removed from the bath of water, 
 should not be allowed to dry before being albumenised, 
 otherwise the albumen is spread with difficulty on the 
 surface, and stains are subsequently produced. 
 
 The albumen should not be applied sparingly to the 
 glass, but at the same time it should not be allowed to 
 flow over to the back of the plate ; if this should happen, 
 it is best removed, when perfectly dry, with some bibulous 
 paper moistened with water. 
 
 Walking about the room when the albumenised glasses 
 are being left to dry should be avoided as much as 
 possible, so as to prevent any particles of dust, <fec., 
 settling on them. In about twelve hours they will be 
 sufficiently dry, when they can be preserved for an in- 
 definite time, if placed in a grooved box to protect them 
 from damp and the direct light of day. 
 
 All the foregoing operations are to be done in the 
 dark room, and when finished, the water in the large 
 bath may be thrown away, but that in the smaller bath 
 of gutta-percha should be retained, for the purpose of 
 precipitating the silver it contains, as before described. 
 
 The following is a resume of the first series of opera- 
 tions, in their proper order, that each glass undergoes : 
 
 1. Cleaning. 
 
 2. Coating with collodion. 
 
 3. Sensitising. 
 
 4. Washing for a few moments in the first bath of 
 
 water contained in the gutta-percha vessel. 
 
 5. Washing a second time in a bath, where it is left 
 
 for several minutes. 
 
78 PHOTOGRAPHIC PROCESSES. 
 
 6. Leaving to drain. 
 
 7. Coating with iodised albumen, which, has been 
 
 before used for removing the excess of water. 
 
 8. The immediate application of another coating of 
 
 fresh iodised albumen. 
 
 9. Lastly, leaving it to drain and dry. 
 
 On the evening, or at most the day before requiring to 
 use the plates for taking views, they must be submitted 
 to a second series of operations, so as to render the 
 iodised albumen surface sensitive to light. 
 
 A great number of albumenised glasses may by pre- 
 pared at a time, because they can be kept for an indefinite 
 period ; whereas, no greater number of them should be 
 sensitised than will be used in a very short time, as they 
 then rapidly deteriorate by keeping. 
 
 For sensitising the glasses a bath of aceto-nitrate of 
 silver is required, composed of 
 
 Distilled Water 16 ounces 
 
 Glacial Acetic Acid 1 
 
 Fused Nitrate of Silver , H 
 
 This bath requires to be filtered before being used, and 
 a gutta-percha dish should be employed for it. After 
 being used for a few weeks it becomes of a yellowish 
 tint, that can, however, be removed by being shaken up 
 with some kaolin. As a matter of precaution the kaolin 
 may always remain at the bottom of the bottle, and the 
 liquid decanted from it when used. 
 
 At the side of the bath of aceto-nitrate of silver should 
 be placed another of much larger size, filled with filtered 
 rain-water. 
 
 An albumenised glass is immersed with one quick 
 movement into the aceto-nitrate of silver, and left there 
 for fifteen seconds or more, it is then placed in the bath 
 of rain-water, which is shaken a short time so as to 
 remove the excess of nitrate of silver. This being done, 
 it is taken out of the water and left to dry against the 
 wall in the manner previously described. It is almost 
 needless to say that the operation of sensitising must be 
 done in the dark room with a yellow light. The glasses 
 thus sensitised, when dry, are ready to receive the im- 
 pression in the camera, after which they can be kept for 
 
THE COLLODIO-ALBUMEN PROCESS. 79 
 
 a fortnight before being developed, although, as a rule, 
 the shorter time that elapses between the sensitising and 
 development the better will be the result. To obtain 
 good proofs, not more than three days should intervene 
 between the two operations. In summer especially, the 
 time should be as short as possible ; in winter it may be 
 longer without so much risk of injury. 
 
 The sensitised glasses ought to be preserved in grooved 
 boxes free from chinks or cracks through which the 
 daylight might pass, and kept as dry as possible. 
 
 When required for use they are placed in the ordinary 
 collodion frame for views. There are, however, some 
 frames particularly devised for dry plates, which hold 
 two glasses and have two slides, first one of the glasses 
 is exposed to the light, and then the other, by simply 
 turning round the frame. 
 
 The time of exposure for a collodio-albumenised plate 
 is fully double or treble that required for ordinary collo- 
 dion. Experience alone will guide the operator in this 
 particular. 
 
 As the pictures are generally developed after returning 
 from an excursion, it is an excellent plan, to ensure a 
 good proof of any particular view, building, &c., to take 
 two impressions, but with different times of exposure. 
 
 The collodio -albumen process is also particularly well 
 adapted for obtaining transparent positives on glass. 
 For this purpose the sensitised surface of the prepared 
 plate is put in contact with the varnished surface of the 
 negative, and placed in a close frame similar to that used 
 for exposing the plate in the camera. By opening the 
 sliding shutter the diffused light of day is allowed to act 
 for three or four seconds, taking care that in arranging 
 the glasses in the frame, the light passes through the 
 negative before striking the sensitised plate. The plate 
 is then taken into the dark room, and developed in the 
 ordinary manner. 
 
 When this process is followed the positive picture 
 obtained has a very good effect if placed before a win- 
 dow ; it should be mounted with a plate of ground glass, 
 the albumenised surface of one in contact with the 
 ground surface of the other, and the two plates united 
 by a border of black paper pasted round the edges. 
 
80 PHOTOGRAPHIC PROCESSES. 
 
 The following is the method of developing the col- 
 lodio -albumen plateo : 
 
 Place in a porcelain capsule 15 grains of gallic acid, 
 and pour over it 3 ounces of hot distilled water, and 
 mix them well with a glass rod ; when the gallic acid is 
 dissolved, or nearly so, add 13 ounces of cold water, and 
 filter the whole into a bottle for use. 
 
 This liquid is poured into a porcelain dish to about 
 the depth of an inch, and to each quantity of three ounces 
 employed is to be added one -fourth of a drachm of the 
 following solution : 
 
 Distilled Water 35 ounces. 
 
 Fused Nitrate of Silver 230 grains. 
 
 Glacial Acetic Acid 9 minims. 
 
 And care should be taken that the whole be thoroughly 
 mingled together, otherwise stains will be formed on the 
 surface of the negative. 
 
 The exposed albumenised plate is to be quickly 
 plunged into this liquid, the coated surface upwards, 
 and raised up and down for several times by means of a 
 hook so that the fluid flows well over its surface. It is 
 necessary that the porcelain dish should be adapted for 
 the purpose, and with a flat bottom so that the glass 
 may be perfectly immersed in the solution. 
 
 At the end of the first hour or two the sky and other 
 parts highly illuminated will hardly have made their 
 appearance, but in the succeeding two hours the proof 
 usually comes out with extreme vigour. It is always 
 well to watch this operation so as to stop it so soon as 
 the development is complete, which, however, sometimes 
 takes as long as twelve hours. The colder the weather 
 the longer the time required. In winter it is preferable, 
 and sometimes necessary, to develop in a warmed 
 apartment. 
 
 Very often in about three or four hours the develop- 
 ment of the image can be accelerated by renewing the 
 gallic acid and doubling the dose of nitrate of silver, 
 that is to say, to each 3 ounces of solution of gallic acid 
 add a half instead of a quarter drachm of the aceto- 
 nitrate of silver; but if this is done the dish must be kept 
 agitated, otherwise the particles of reduced silver which 
 
THE COLLODIO-ALBUMEN PROCESS. 81 
 
 are formed would attach themselves to the picture and 
 entirely spoil it. 
 
 To succeed well, two conditions are indispensable a 
 warm room, about 68 Fahr., and a slow development. 
 It is also very important that the gallic acid should not 
 be allowed to become coloured and muddy ; if this should 
 happen, the glass must be washed, so as to remove the 
 thick and decomposed gallic acid from its surface, and 
 placed in another dish with some fresh solution of gallic 
 acid, to which has been added a less quantity of aceto- 
 nitrate of silver than was employed at first. 
 
 This last observation is most important, and the opera- 
 tion is one that cannot be too often repeated ; with a 
 proper attention to the time of exposure and consequent 
 regulation of the doses of gallic acid, the picture should 
 be well and perfectly developed in about four hours. 
 
 To finish off the proof, it is washed with water when 
 taken from the gallic acid bath, and fixed with hypo- 
 sulphite of soda in the manner described for the ordinary 
 wet process a final washing completes the picture. It 
 is useless to varnish the plate, as the albumen itself 
 forms an excellent preservative coating. 
 
 As the beauty of a collodio-albumen proof greatly 
 depends upon the proper time of exposure in the camera, 
 it may be useful to give some of the indications of a too 
 short or too lengthened action of light. 
 
 If the exposure has been too short, the picture does 
 not come out well even after twelve hours of develop- 
 ment and repeated changing of the gallic acid solution, 
 the sky alone is distinctly marked, all the other parts of 
 the proof have *a general grey tint, without the least 
 vigour. Nothing can remedy this fault. If, on the con- 
 trary, the exposure has been too long, the sky shows 
 itself very quickly, as well* as the other light parts of the 
 picture. In* about an hour the proof exhibits a con- 
 siderable amount of intensity in all its details. If the 
 development be now stopped, a passable picture may be 
 obtained ; but if it be continued, the whole of the image 
 becomes grey, and the sky, although apparently very 
 dark, because viewed by reflection from a white ground, 
 is, nevertheless, also grey. Over exposure is likewise indi- 
 cated by a red tint, which the proof takes after being fixed. 
 F 3 
 
82 PHOTOGRAPHIC PROCESSES. 
 
 "When the time of exposure has been correct, the sky 
 begins to show itself in about an hour, and very gradually 
 increases in intensity, and becomes of an absolute black, 
 even when viewed as a transparency after fixing. The 
 whole of the details are shown with great vigour, while 
 the shadows are perfectly transparent. 
 
 If the sky should not be sufficiently dark, and it is not 
 possible to take another proof, recourse may be had to 
 stopping out with a little Indian ink mixed with honey 
 and water, and a soft camel's hair pencil. It is,however, 
 next to impossible to do this operation in such a manner 
 that some of the details on the horizon are not injured. 
 
 3. The Tannin Process. 
 
 This dry process derives its name from the use of 
 tannin a bitter principle obtained from gall-nuts 
 as a preservative agent. To Major Russell is due the 
 credit of having introduced it. 
 
 The glass to be prepared should be cleaned with great 
 eare, particularly from any greasy substances. This is 
 conveniently done with a mixture of Tripoli powder, 
 spirits of wine, and solution of ammonia. A tuft of 
 cotton is dipped into this mixture and rubbed over its 
 surface for a minute or so ; then well rinsed in water and 
 rubbed dry with a clean cloth. 
 
 The glass, just before being used, should be wiped 
 with a perfectly dry and warm cloth, and then coated 
 with the following solution : 
 
 Nelson's Patent Gelatine ; 20 grains. 
 
 Distilled Water 10 ounces, 
 
 Alcohol \ ounce. 
 
 Dissolve and filter; this solution will keep good for a 
 considerable time. 
 
 This gelatine solution is applied to the glass in the same 
 way as ordinary collodion, taking care that the whole of 
 the surface is covered, and that the back of the plate be 
 not soiled. The superfluous liquid is received back into 
 the bottle, and the plate set to dry, as shown at Fig. 69 ; 
 when well drained, remove the accumulation of fluid very 
 carefully from the lower edge of the plate by a piece of 
 
THE TANNIN PROCESS. 83 
 
 blotting-paper drawn along it. When the surface is dry, 
 warm gently by the fire, and retain for use in a grooved 
 box. As plates thus coated will keep good any length of 
 time, any required number may be prepared, taking care 
 that the backs of them are quite free from stains of gelatine. 
 
 The gelatinised glass is now coated with old iodised 
 collodion in the usual manner, taking particular care that 
 the whole surface of the plate be covered; it is then im- 
 mersed in the silver-bath employed for the wet collodion 
 process (page 34), and allowed to remain in it from 
 three to five minutes. 
 
 Remove the sensitive plate from the bath, and wash it 
 freely under a water-tap for about a minute, it will then 
 be ready to receive the preservative solution, composed 
 as follows : 
 
 Tannin 60 grains. 
 
 Distilled Water 4 ounces. 
 
 Filter through paper, and measure out two separate por- 
 tions according to the size of the plate to be prepared, 
 allowing about two drachms in each quantity for a stereo- 
 scopic plate. The first portion of tannin solution is 
 poured over the washed coating of the sensitised plate 
 two or three times, so as to remove the water adherent to 
 it, then the other quantity is poured on and off, and the 
 plate placed on end on a piece of blotting-paper, and 
 allowed to dry in a perfectly dark and warm place. 
 
 After exposure in the camera, which averages from 
 one to three minutes on a favourable day, and from four 
 to eight minutes in dull weather, the picture is to be 
 developed, for which purpose the following solutions are 
 required : 
 
 No. 1. ( p y ro & allic Acid 72 grains. 
 
 I Alcohol 1 ounce. 
 
 Dissolve and keep in a stoppered bottle. 
 
 C Nitrate of Silver 20 grains. 
 
 No. 2. -j Citric Acid 20 
 
 C Distilled Water 1 ounce. 
 
 Dissolve and filter should any white or other precipi- 
 tate be formed. To three ounces of distilled water add 
 half a drachm of No. 1, and if the plate to be developed 
 
84: PHOTOGRAPHIC PROCESSES. 
 
 be a stereoscopic size, take three drachms of this solution 
 and add to it from ten to twenty minims of No. 2 ; this 
 forms the developing fluid. 
 
 The exposed plate is first moistened with distilled 
 water, which must he done quickly and evenly, other- 
 wise stains are produced, and then the developing fluid 
 poured over its surface and kept slightly in motion. 
 The development must be carefully watched, and if in a 
 short time the sky comes out strongly, but. is not followed 
 by the other details of the object, the plate was not long 
 enough exposed, and the developing fluid must be poured 
 back into the measure, and say ten minims of No. 1 
 added, so as to increase the quantity of pyrogallic acid. 
 If the whole of the picture, however, appears to come out 
 at once, a few drops of No. 2 is to be added, so as to in- 
 crease the density of the sky. 
 
 When the picture is properly developed, it is fixed 
 with a solution of hyposulphite of soda, washed and 
 varnished as described lor the wet collodion process. 
 
 CHAPTER XIII. 
 
 POSITIVE COLLODION PROCESS. 
 
 THE positive collodion process is very similar in its gene- 
 ral details to the negative, and will generally be found 
 much easier of manipulation, from its not requiring the 
 like amount of accuracy. 
 
 Preparation of the Collodion. 
 
 Iodide of Cadmium, or Ammonium 15 grains. 
 
 Pyroxyline 15 
 
 Ether 3* ounces. 
 
 Alcohol 1 ,, 
 
 The pyroxyline and the iodide of cadmium are first in- 
 troduced into a dry flask or bottle, and the alcohol poured 
 upon them, and the mixture shaken violently for about 
 a minute ; the ether is then added and the contents fur- 
 ther agitated, and finally set aside all night. The clear 
 supernatant portion may now be carefully poured on from 
 
POSITIVE COLLODION PROCESS. 85 
 
 the white deposit at the bottom of the bottle, or instead 
 of decanting, it may be preferable to use a small syphon 
 bottle as shown at Fig. 23, the action of which has 
 already been explained. 
 
 The positive collodion thus prepared should, like the 
 negative, be preserved in the dark in well corked or stop- 
 pered bottles. 
 
 Should the collodion produce a fogged image, or in 
 other words, if the plate becomes covered with a film of 
 reduced silver, underneath which there is obviously a 
 very good picture, this defect may be remedied by adding 
 to it a few drops of the following solution : 
 
 Alcohol 85 ounces. 
 
 Iodine 150 grains. 
 
 A small quantity of this liquid is added to the collodion, 
 so as to impart a pale amber colour thereto. 
 
 Patent glass plates are not required for direct collodion 
 positives, and the reason is very simple. When negatives 
 are taken they are afterwards applied to sheets of sensi- 
 tised paper with some degree of pressure, in order to 
 obtain the positive impression, on which account it is 
 necessary that the plate should be perfectly flat and 
 free from striae, otherwise the striae would be reproduced 
 upon the paper, and the glass very liable to fracture 
 from the pressure. Such is not the case, however, with 
 direct positives ; here the purity and flatness of the 
 glass is by no means so important, and ordinary flatted 
 crown may therefore be used. Some photographers em- 
 ploy glass of a deep red or purple colour, in which case 
 it is unnecessary to varnish the plate. 
 
 Whatever kind of glass plate be adopted, it should be 
 chosen as flat as possible, otiierwise there will be difficulty 
 in getting them into the camera back; but the colour in 
 no way affects the beauty of the image, any more than 
 bubbles or other mechanical surface detects. 
 
 It has been previously explained, when describing the 
 negative collodion process, how the plate is cleaned, and 
 in what manner the collodion is poured on the glass ; no 
 further remarks are therefore needed on the subject be- 
 yond reminding the reader that the collodion should be 
 poured upon the plate in the dark room, in order to be 
 
86 PHOTOGRAPHIC PROCESSES. 
 
 ready as soon as the film is set to plunge it into the bath, 
 which is composed as follows 
 
 Distilled "Water 35 ounces, 
 
 Fused Nitrate of Silver 2i 
 
 Filter. Prepare also the following solution 
 
 Water 3i ounces. 
 
 Acetate of Ammonia 30 grains. 
 
 And, after filtration, pour it into the bottle which contains 
 the above solution of nitrate of silver. A crystalline pre- 
 cipitate is produced which requires several days to deposit 
 before the bath will be ready for use. It may, however, 
 be used a few hours after mixing by resorting to filtration; 
 but it is always better after a few days' keeping. 
 
 The bottle containing the bath should have a funnel 
 and filter adapted to it, through which the solution ought 
 to be always filtered after use, so as to be ready for each 
 day's work, the same filter serving almost indefinitely. 
 
 The mixture of acetate of silver with the nitrate not 
 only produces increased rapidity, but tends to maintain it. 
 It has, moreover, the advantage of preventing fogging ; 
 but to this end it is necessary to be always kept in the 
 dark. 
 
 The details of manipulation, as before mentioned, are 
 the same as have been described for the negative process, 
 except that the exposure is reduced about three -fourths 
 and the development effected by protosulphate of iron 
 instead of pyrogallic acid. 
 
 A saturated solution of protosulphate of iron is pre- 
 pared by pouring half a gallon of boiling water on two 
 pounds of green vitriol, or ordinary protosulphate of iron, 
 stirring well together ; allow it to cool and then filter. 
 
 This saturated solution is, of course, much too concen- 
 trated for use ; the developing solution is therefore pre- 
 pared from it in the following manner 
 
 Water 18 ounces. 
 
 Saturated Solution of Sulphate of Iron 8 ,, 
 
 Ordinary Acetic Acid of Commerce If ,, 
 
 Ordinary Alcohol 1 
 
 Sulphuric Acid 1 ,, 
 
 This solution should be contained in a vertical bath with 
 a dipper, and the plate immersed therein for fifteen seconds 
 
POSITIVE COLLODION PROCESS. 87 
 
 after exposure, which will be found amply sufficient to 
 develop the picture in all cases. 
 
 On withdrawal from the bath the image ought to possess 
 very little intensity, if otherwise it might be regarded as 
 an indication that the proof would not be a satisfactory 
 one. However this may be, the plate is now well washed 
 with water, fixed with cyanide of potassium, and dried as 
 has been described under the negative process. 
 
 It is only after fixing that a correct idea can be formed 
 as to whether the exposure has been correct or not, and 
 practice alone will enable the operator to determine the 
 point. If any trace of fogging should become apparent, 
 a few drops of the alcoholic solution of iodine may be 
 added to the collodion, the formula for which has been 
 already given. 
 
 It may not be out of place here to give a few explana- 
 tory remarks in order that the reader may fully com- 
 prehend the essential difference between a positive and 
 negative collodion picture. 
 
 A negative proof being intended to possess varying 
 degrees of opacity to transmitted light, it is necessary 
 that the film should have in it a sufficient quantity of 
 material to suffer various amounts of decomposition in the 
 process of development ; to this end, not only is a thick 
 collodion employed, but also one fully charged with iodide. 
 
 With a positive the case is entirely different, the film 
 is extremely thin, for unless it were so the whole would 
 be patchy, owing to the light having penetrated the film 
 and effaced the delicate details by reflection. It is, 
 therefore, of the highest importance to use the thinnest 
 possible collodion, which yields, on leaving the bath, a 
 film only faintly opalescent. 
 
 For fixing, cyanide of potassium is a more appropriate 
 agent than hyposulphite of soda, as it yields a more 
 agreeable t'one. It requires, however, to be used with 
 great care on account of its highly poisonous character. 
 The removal of the unaltered iodide by its means may 
 be effected either by immersion or by pouring the solution 
 over the plate. The fixing solution is prepared by mixing 
 together 
 
 Water 35 ounces. 
 
 Cyanide of Potassium li to 3 ounces. 
 
88 PHOTOGRAPHIC PROCESSES. 
 
 Longer contact of the cyanide than is absolutely neces- 
 sary should be avoided, as the delicate detail is apt to 
 suffer, and when the iodide is removed, which may be 
 ascertained by the transparency which the plate acquires, 
 it should be freely washed with water, dried, and var- 
 nished. 
 
 The varnish, if the picture be taken on a colourless 
 glass, must be black on the plain side, and colourless or 
 " crystal varnish " on the film side ; when purple glass, 
 however, is used, the black varnish may be dispensed 
 with. 
 
 A solution of gum arabic is sometimes poured over the 
 film side of the plate, instead of varnish. Some operators 
 omit all kind of protection; this is, however, a mistake, 
 as pictures which are not covered either with gum arabic 
 or crystal varnish, very quickly assume a tarnished and 
 disagreeable aspect. 
 
 To communicate an extra amount of whiteness to direct 
 positives they are sometimes treated with bichloride of 
 mercury after the final washing ; the general tone, how- 
 ever, is usually sufficiently cold, and therefore its employ- 
 ment cannot be recommended in an artistic point of view. 
 
 The method of operating is as follows : Cold distilled 
 water is allowed to take up as much bichloride of mer- 
 cury as it will, and, the solution being filtered, the positive 
 is immersed therein until it assumes an appearance as white 
 as snow, which will be in about one minute, after which it 
 is washed and varnished in the usual way. These proofs 
 should be preserved from the direct action of the sun's 
 rays, otherwise they become very much weakened in a 
 few months. 
 
 The different methods of mounting in passe-partouts, 
 (fee., involve operations of so strictly mechanical a nature 
 that they need not be entered into in this place, as the 
 means of carrying them out are soon acquired by practice. 
 
 Glass positives are very easy to take, although some 
 practice is necessary to attain to any great degree of 
 excellence. The pictures should have a mirror-like 
 aspect, and the blacks extremely pure. Sometimes a 
 certain amount of fogging takes place, marring the bril- 
 liancy of the picture; this may be removed by washing 
 the picture while still wet, immediately after fixing, with 
 
THE STEREOSCOPE. 89 
 
 an alcoholic solution of iodine of 15 grains to the ounce. 
 The length of time must be determined by the extent 
 of the fogging, and can only be ascertained by practice. 
 When it is considered that the action of the iodine has 
 been sufficiently prolonged, it is washed off, and the plate 
 again immersed in the cyanide fixing bath, and finally 
 washed and dried. 
 
 CHAPTER XIV. 
 
 THE STEREOSCOPE. 
 
 THIS instrument shows in relief, as one picture, two dis- 
 similar views of the same object, mounted together either 
 on plate or paper. The following is an explanation of 
 this singular phenomenon. If, for example, a square- 
 based pyramid be examined with the left eye, the eye 
 being placed in the axis of this pyramid, it is very 
 evident that it will present the appearance of a square 
 intersected by its two diagonals, and a drawing of it 
 would, in fact, be represented by such a figure. But if 
 the left eye be now closed, and the right eye opened, it is 
 equally clear that one side of the pyramid will be more 
 visible than the other, and that in proportion to its 
 height. 
 
 Now, if this same pyramid be viewed with both eyes 
 at the same time, the two different images combine upon 
 the retina in such a way as to produce the appearance of 
 a single solid pyramid, in perfect relief, or, in other words, 
 the effect is stereoscopic. 
 
 If the pyramid, instead of being in relief, were hollow, 
 and the left eye, as before, placed on a line with its axis, 
 a square figure intersected by its two diagonals will be 
 seen; but immediately upon opening the right eye, the 
 effect will be exactly the reverse of what occurred in the 
 case of the figure in relief. In the former case, it was 
 the side of the pyramid to the right which impinged 
 mostly on the right eye, but in the case of the hollow 
 
90 
 
 PHOTOGRAPHIC PROCESSES. 
 
 figure, it would be, on the contrary, the left eye which 
 receives the larger impression, and in consequence thereof, 
 the effect upon the two eyes would be different, and 
 instead of producing the sensation of solidity or relief, 
 the combined images produce the appearance of tollow- 
 ness, or in other words, are pseudoscopic. 
 
 It is upon this principle that the stereoscope is founded, 
 the two views employed together are each taken by a 
 camera, as near as possible under the same conditions as 
 naturally presented to each eye. The prismatic glasses 
 of the instrument superpose the two views in such away 
 that but one image is percieved by the two eyes, and 
 that in relief. 
 
 To Professor Wheatstone is due the credit for the 
 elaboration of this theory and the application of photo- 
 graphy thereto ; also the invention of one modification of 
 the instrument. Mirrors were employed in its construc- 
 tion, and it is known as the reflecting stereoscope. Sir 
 David Brewster replaced the mirrors by prisms, and it is 
 this improvement which has rendered it so popular and 
 portable. 
 
 The relief of near objects is easily explained, by the 
 
 large angle formed by the 
 visual rays brought to 
 each eye ; but as this angle 
 becomes more and more 
 diminished in proportion 
 to the distance of the ob- 
 jects, it becomes at last 
 very difficult to appreciate 
 relief, and inconsequence, 
 the situation of large 
 masses can only be judged . 
 of by comparison with 
 those which are near. 
 
 The original stereo- 
 scope was composed of 
 small half lenses, which 
 Fig. 75. Prismatic stereoscope. turned in brass tubes in 
 such a way as completely to superpose the two views ; but 
 now the small lenses are replaced by large square prisms, 
 let into the upper portion of the stereoscope, and this not 
 
THE STEREOSCOPE. 91 
 
 only affords a larger field of view, but also makes the 
 instrument more easy to manage. 
 
 Fig. 75 represents a prismatic stereoscope. The slides to 
 be viewed are introduced through a groove at the bottom ; 
 it is furnished with a centre partition, which assists in the 
 superposition of the two images. The upper portion is 
 shown detached, or open, the better to exhibit its general 
 construction. 
 
 For the best instruments the two prisms are achromatic, 
 or else replaced by two achromatic lenses, by which their 
 definition is rendered as perfect as possible. A very con- 
 venient form of stereoscope for showing a number of 
 slides is now constructed, whereby as many as fifty pic- 
 tures can be viewed consecutively, by merely turning a 
 small button. This arrangement consists of a stereoscope 
 fixed at the top of a deep box containing the views, 
 which are attached to a kind of endless chain, on moving 
 which the pictures are presented as required. 
 
 There are many other forms of stereoscope, the whole 
 of which, however, with the exception, perhaps, of the 
 reflecting stereoscope for viewing large pictures, being 
 constructed on the general principle and arrangements of 
 the foregoing, any further description would be un- 
 necessary. 
 
 Stereoscopic views are always of small size, except 
 
 Fig. 76. Twin-lens Camera with Double Back. Fig. 77. 
 
 those before mentioned for the reflecting stereoscope, and 
 are taken on glass and paper ; those on glass are viewed 
 as transparencies, but the paper slides are examined by 
 reflected light, for which purpose there is usually attached 
 
92 PHOTOGRAPHIC PROCESSES. 
 
 to the stereoscope some such contrivance as is represented 
 at Fig. 75, like a small door in front. 
 
 The most simple method of obtaining stereoscopic 
 pictures certainly consists in taking the two proofs at the 
 same time, with the apparatus as represented in Fig. 76. 
 It is composed, 1st, of two double achromatic combinations 
 of exactly the same focal length ; 2nd, of an ordinary 
 expanding camera, furnished, however, with a back, having 
 two shutters (Fig. 77). 
 
 The following is the method of operating : 
 
 Whenever the two lenses are not exactly to the same 
 focus, it is necessary to begin by focussing a near object, 
 such, for instance, as a plaster bust. When a perfectly 
 sharp image is obtained upon the ground glass with each 
 of the lenses, the rack and pinion adjustment must not 
 be again touched, but the focussing of any subsequent 
 figure must be accomplished by drawing in or out the 
 expanding or inner body of the camera. 
 
 This, however, will not suffice, if the distance of the 
 bust from the camera has not been so regulated as to be 
 that which will be most suitable for a portrait. For this 
 apparatus will serve only for portraits, and that, too, for 
 portraits taken at a very short distance ; otherwise, the 
 proofs will be wanting in relief. 
 
 As would be inferred from the shape of the back, a 
 glass is chosen much longer than it is wide, upon which 
 the two negatives are taken at the same time. The 
 prints obtained from these negatives are reversed, that is 
 to say, when each positive is cut for the purpose of being 
 mounted upon card, it will be necessary to paste the left- 
 hand picture on the right side of the card, and the right- 
 hand print on the left of the card. 
 
 When, with this apparatus, it is desired to take views, 
 a diaphragm or stop must be inserted between the two 
 lenses, but the two proofs can, however, no longer be 
 taken at the same time, for the distance between the two 
 lenses is not sufficient to give the proper amount of 
 stereoscopic relief for distant objects. 
 
 A board with moveable guides is therefore placed upon 
 the camera-stand, as represented at Fig. 81, and two 
 cross lines are drawn upon the ground glass of the 
 camera. One marks the centre on one side ; the second, 
 
THE STEREOSCOPE. 93 
 
 that on the other. The camera is then pointed in such a 
 way that the same object in the landscape comes on 
 the centre of the cross lines, for without this the proof 
 would not be properly centred. 
 
 The two negatives then are taken separately, and 
 require transposing when they are mounted on the card. 
 But this reversing or transposition may be, however, 
 accomplished in the instrument itself, so effectively, that 
 when the negative is placed in the stereoscope, the 
 objects appear in relief. 
 
 For this purpose, suppose the apparatus, Fig. 76, is in 
 the position as represented in Fig. 81. Instead of taking 
 with the right-hand lens the right-hand negative, and 
 with the left-hand lens the left-hand negative, let the ope- 
 rations be reversed. Take the left picture with the right 
 lens, and vice versd the right picture with the left lens. 
 
 When it is desired to take landscapes only, the camera 
 represented in Fig. 78 is generally used. It is an ordinary 
 quarter-plate camera, which is converted into a stereo- 
 scopic camera by the addition of three pieces of apparatus, 
 two of which are represented in Figs. 79 and 80. 
 
 In Fig. 79 will be seen a grooved piece of wood, with 
 two rebates and a catch in the middle of the upper one, 
 and a ground glass sliding between them ; this is stopped 
 in the middle by the catch before mentioned. This 
 piece of wood is screwed to an ordinary camera-back, 
 the door of which is reversed. 
 
 Two diagonal lines are drawn upon the ground glass. 
 When it is desired to take a stereoscopic view, the board 
 with two moveable rebates, 
 as represented in Fig. 81, is 
 brought into use. 
 
 The following is the method 
 of proceeding. The camera, 
 Fig. 78, is first placed in one 
 of its positions, and directed 
 towards the view then in 
 the second position, and 
 directed towards the same 
 point. These two views will **' 78 ' ^Tfew" &tereuscopic 
 appear upon the ground glass exactly the same, but 
 they are not so in reality. 
 
94: PHOTOGRAPHIC PROCESSES. 
 
 The ground glass being withdrawn, the camera is placed 
 on the right hand of the operator, who looks at the view 
 which is- before him. Replacing the focussing glass by 
 the camera-back, which is introduced on the right side 
 of the piece of wood (Fig. 79), it is obvious that it is 
 
 Fig. 79. Frame with Ground Glass. Fig. 80. Frame for Sensitive Plate. 
 
 that part of the glass which is on the left in the back 
 which will be first uncovered, as is shown in Fig. 80. The 
 slide being drawn, and the time of exposure having 
 expired, the door is closed. Fig. 78 shows the position 
 of the camera for the first picture, that is to say, the right- 
 hand one. 
 
 In the second position, that of the left, the camera- 
 back is made to slide between the two rebates until it is 
 checked by the brass catch; the second picture is then 
 taken. 
 
 These directions seem complicated, but in practice they 
 prove very simple. The principle being once understood, 
 it is easy to follow the description. 
 
 There remains a third method of operating, which 
 is still more difficult. When it is desired to take views 
 of animated objects or groups, the necessary interval 
 which elapses between the two positions of the camera, 
 just described, renders it inapplicable for the purpose, 
 as in all probability the objects must have moved, and 
 the two views would not be alike. Under these cir- 
 cumstances two quarter-plate cameras are used, furnished 
 with lenses whose focal lengths are exactly equal, and 
 the operation is conducted as is shown in Fig. 81. Great 
 care must be taken to open and close the two shutters at 
 the same time, or at least very quickly one after the 
 other, as it is obvious that if one plate be longer exposed 
 
THE STEREOSCOPE. 95 
 
 than the other, the development must take place un- 
 equally, and the two proofs will be unequal also. 
 
 Fig. 81. Position of the two Cameras for Instantaneous Views. 
 
 In order that the two negatives should be exactly 
 alike, the two plates should be collodionised at the 
 same time, and immersed one after the other in the same 
 nitrate -bath, from which they should be simultaneously 
 withdrawn. 
 
 In reference to the development, a dish is used with 
 a glass bottom and wooden sides, or of solid glass, 
 and the two plates are placed therein, one by the side of 
 the other, in order that both may be developed with 
 the same pyrogallic acid. This is the only way to 
 obtain proofs of nearly equal intensity, for it is, indeed, 
 quite a chance that they should be exactly alike ; a 
 little difference will not, however, materially affect the 
 result in printing. 
 
 Positive proofs should be reversed: the one which was 
 taken on the right should be on the left in the card, and 
 in order that this may always be done correctly, it is 
 advisable to mark each of the negatives when taken 
 separately. 
 
 The apparatus for cartes de visite, at page 39, is, in 
 fact, nothing more than the apparatus, Fig. 76, with 
 a back like Fig. 80. It consists of a camera to which 
 four lenses of equal focal length have been adapted, 
 furnished with a sliding back. From this arrangement 
 it follows that when the lenses are arranged as shown in 
 Fig. 76, there will be eight negatives taken on each plate, 
 and that each pair will be stereoscopic. The cost of the 
 apparatus may, however, be materially lessened by using 
 a whole-plate camera fitted with a pair of twin-lenses, 
 
96 PHOTOGRAPHIC PROCESSES. 
 
 as in Fig. 76, and arranged so as to slide together on its 
 rising front ; in this way four carte de visite pictures may 
 be obtained on one plate. A number of negatives are 
 taken on one plate, because the printing of an equal 
 number of proofs separately would be much more costly 
 and troublesome. 
 
 It remains to consider the proper angular distance 
 which should separate the two cameras represented in 
 Fig. 81, so as to produce the desired result. 
 
 If several square-based pyramids, of various heights, 
 be placed successively on the same spot, and examined 
 with one eye from a fixed point over and slightly to the 
 side of the pyramids, it will be perceived that each time 
 a pyramid is changed, that the relative position of the 
 apex alters, and that this displacement is greater the 
 taller the pyramid viewed, or in other words, the relief 
 is more visible. If these pyramids be now viewed again 
 with one eye, but this time not on one side, but directly 
 on a line with their axes, they will, although all differ- 
 ing in height, nevertheless present the same appearance 
 of a square cut with its diagonals. 
 
 Thus, each time that the height of the pyramid varies, 
 the visual angle becomes greater, and the relief is con- 
 sequently more striking. 
 
 But suppose for a moment that it is desired to repro- 
 duce the pyramid, what angle should be employed? 
 should it be the angle of vision, or a larger one ? 
 
 In view of what has been said above, it is evident 
 that if a larger angle be used, the pyramid will appear 
 in the stereoscope higher than it really is, and as the 
 photographic apparatus does not furnish any standard 
 of comparison by means of an object of known height 
 placed side by side, a false idea will be conveyed of 
 the true size of the pyramid. 
 
 When the angle is too great, the object is distorted. 
 This defect is, so to speak, very general in all repro- 
 ductions of statues, portraits, &c. The relief in these 
 cases is, with very few exceptions, greatly exaggerated. 
 And thus it happens that when a statue is reproduced in 
 this way, the- head often seems so much in advance, that 
 it becomes really monstrous. 
 
 It should always be borne in mind when objects are to 
 
THE STEREOSCOPE. 97 
 
 be reproduced which are of known size and proportions, 
 such as statues, portraits, animals, &c., that if a large 
 angle be employed the image will be distorted. 
 
 For views and landscapes an excessive relief may be 
 obtained without detriment to the picture, on the con- 
 trary, with a decided improvement in effect, at the same 
 time attention must be had to the character of the view. 
 If, for example, the foreground of the picture be very 
 near the operator, a small angle (about 2) must be used, 
 otherwise the two pictures will not become superposed in 
 the stereoscope. If, on the contrary, the view offers but 
 little difference between the various planes, advantage may 
 be taken of this, and a larger angle, - for example, may 
 be employed. 
 
 The stereoscopic angle is reckoned from the nearest 
 point of the view to be taken; this point forming the 
 apex of the triangle, and the distance between the two 
 cameras being the base, or rather the arc, of the angle. 
 
 When the operator has chosen his point of sight, the 
 eye should estimate the difference between the cameras 
 and the nearest point in the view to be taken, which will 
 determine whether an angle of 2 or 4 be preferable. 
 The following table will, to a certain extent, serve as a 
 guide for beginners to judge the value of an angle, that 
 of 2 being selected as an example : 
 
 Distance of the Object from the Cameras. Distance between the Cameras. 
 
 Yards. Inches. 
 
 1 1-26 
 
 2 2-52 
 
 3 3'78 
 
 4 5-04 
 
 5 6-30 
 
 6 7'56 
 
 7 8-82 
 
 8 10-08 
 
 9* 31-34 
 
 10 12-60 
 
 15 18-90 
 
 20 25-20 
 
 25 31-68 
 
 30 37'80 
 
 35 44-28 
 
 40 ... 50-40 
 
98 PHOTOGRAPHIC PROCESSES. 
 
 CHAPTER XV. 
 
 PRINTING POSITIVE PROOFS. 
 
 THEORETICALLY, the printing process is one of the greatest 
 simplicity : One side of a sheet of paper is first imhued 
 with a solution of common salt, and dried ; it is then 
 treated with a solution of nitrate of silver. A white 
 substance, called chloride of silver, is formed in the texture 
 of the paper, which has the singular property of becoming 
 rapidly darkened on exposure to the sun ; it is on this 
 account that when it is prepared the operation should be 
 performed in the absence of daylight, and the sensitive 
 paper preserved in a dark box. 
 
 It is evident that if paper so prepared be placed behind 
 a negative, and exposed to daylight, a positive image will 
 be produced on the paper. And, in order to its preserva- 
 tion, it will be necessary to remove the whole of the chloride 
 of silver unacted on by light, without affecting those por- 
 tions which constitute the image ; this is readily accom- 
 plished by soaking the proof for a quarter of an hour in a 
 solution of hyposulphite of soda, and then washing most 
 copiously in water to remove every trace of this fixing 
 agent from the texture of the paper. 
 
 The proof thus completed is the final result of all the 
 operations which have been previously described. 
 
 The foregoing description gives the general principles 
 of the printing process ; a successful result, however, can 
 only be attained by the exercise of the greatest care and 
 attention to many important details, which will be treated 
 of under the following heads : 
 
 1. Salting the paper, that is, treating the paper with a 
 
 solution of common salt, or chloride of ammonium. 
 
 2. Sensitising the paper, by floating on a. solution of 
 
 nitrate of silver. 
 
 3. Exposing the prepared paper to light, and the 
 
 apparatus used for this purpose. 
 
 4. Fixing the image formed bv lioht, and imparting 
 
 an agreeable tone. 
 
 5. Mounting the proofs, that is to say, giving the final 
 
 touches before delivering them to the public. 
 
SALTING THE PAPER. 99 
 
 1. Salting the Paper. 
 
 Suitable paper for positive proofs is now manufactured 
 expressly for the purpose, and can readily be obtained 
 both in England and on the continent. It is not, how- 
 ever, every sheet in the ream as obtained from the manu- 
 facturers that ought to be employed. Those that are 
 uneven in texture, and blemished with black and other 
 spots, must be rejected. 
 
 While selecting paper it is important to touch only the 
 edges of the sheets, because, however dry the fingers may 
 be, they always leave a slight imprint which, sooner or 
 later, will produce a stain. 
 
 It is also necessary to ascertain the right side of the 
 paper to which the chemicals should be applied; this 
 may be done by examining the paper by reflected light, 
 and is that side most uniform in its character and freest 
 from lines. Each sheet, as selected, should have the 
 wrong side distinguished by a pencil mark. 
 
 Positive paper should be moderately thick. A ream 
 should weigh about 22 Ibs., the size being 22 inches by 
 17 inches; but, generally speaking, for albumenised paper, 
 the ream should not weigh less than 24 Ibs., especially if 
 it be required highly glazed ; while for ordinary salted 
 paper a weight of 18 Ibs. to the ream will be found suf- 
 ficient. The paper may be salted with various chlorides, 
 such as the chlorides of barium, strontium, potassium, 
 ammonium, &c. ; and although it was once thought that 
 each salt imparted a characteristic tint to the proof, a 
 contrary opinion is now entertained ; however, chloride of 
 sodium, or common salt, which is always to be obtained 
 in a fair state of purity, is now generally used. 
 
 The salt is dissolved in distilled, or rain-water, in the 
 proportion of 12 grains to the ounce, and the solution fil- 
 tered into a dish large enough to hold a whole sheet of 
 paper, and measuring, therefore, about 24: inches by 
 19 inches. The preparation of whole sheets of paper at 
 one time will generally be found most advantageous, and 
 they are afterwards easily cut to any smaller sizes that 
 may be required. 
 
 The paper is spread out or floated on this solution in 
 the following manner : The opposite ends of the sheet 
 F 2 
 
100 
 
 PHOTOGRAPHIC PROCESSES. 
 
 are held, and the paper bent as represented in Fig. 82, 
 and the middle of the paper being brought into contact 
 with the liquid, the two ends are regularly lowered until 
 the whole of one side just floats on the surface. The side 
 of the paper previously marked with a pencil should be 
 uppermost. 
 
 The paper ought to remain on this bath five minutes in 
 winter and three minutes in summer, at the end of which 
 
 Fig. 82. Salting the Paper. 
 
 time it is withdrawn by means of a pair of horn or box- 
 wood forceps and held for a little while over the dish, to 
 drain ; it is then attached to two clips, or other means 
 of suspension, and hung on a line to dry (Fig. 84). 
 
 If the operator, or rather amateur, should not be often 
 performing this operation it may be found more conve- 
 nient to use smaller sheets, and to suspend them in the 
 manner indicated in Fig. 83; whichever method of sus- 
 pension, however, is adopted, a small piece of white 
 bibulous paper should be attached to the lower corner or 
 corners, in order to aid the draining. of the salt solution. 
 
 Paper thus salted is preserved in a portfolio, and, as it 
 does not undergo any alteration by keeping, it may be 
 prepared in large quantities at a time. 
 
 Albumenised paper yields positive proofs of great 
 
SALTING THE TAPER. 
 
 101 
 
 delicacy and fine colour. It is, however, a little more 
 difficult to prepare. 
 
 White of egg is heaten into a snow-white froth, add- 
 ing, for each 10 eggs, 150 grains of salt, reduced to fine 
 
 Harginj the Paper to Dry. 
 
 Fig. 84. 
 
 powder ; then, when the albumen has accumulated by 
 being allowed to remain at rest (see Fig. 74, and pages 75, 
 76), it is poured into a large flat porcelain tray, and used 
 , in the same manner as the ordinary salting-bath, except 
 that the viscous nature of the albumen requires greater 
 care in floating. 
 
 It is very difficult to albumenise large sheets of paper. 
 The first operation should be the removal of bubbles by 
 means of a card, and this must be done very effectually, 
 because wherever there is a bubble the liquid does not 
 touch the paper, and the consequence is a white spot in 
 the print. 
 
 It is advisable to keep the paper which it is intended 
 to albumenise in a clamp place for a few days before 
 using, otherwise it gets into folds on the liquid, and 
 bubbles are sure to form. When, however, the paper is 
 damp it spreads with the greatest facility on the albumen- 
 
102 
 
 PHOTOGRAPHIC PROCESSES. 
 
 bath, and no fear need be entertained as to the formation 
 of the fatal bubbles. These precautions are specially 
 applicable to large sheets, the small ones being compara- 
 tively easy of manipulation. 
 
 The large sheets are very difficult to suspend. An 
 excellent plan is to attach the sheets, on being withdrawn 
 
 Fig. 85. Drying of Large Sheet?. 
 
 from the bath, to frames of cardboard by the aid of pins, 
 as shown in Fig. 85. In this way the tearing of the 
 sheet, and its frequent falling to the ground, is avoided. 
 
 There is not much purely albumenised paper used ; 
 that which has been prepared with a mixture of albumen 
 and water being preferred, on account of the more 
 moderate brilliancy given to the sheets. From 10 to 40 
 per cent, of water may be added to the pure albumen; 
 but the more water, the less brilliant the paper. 
 
 For portraiture a paper prepared with pure albumen 
 
SENSITISING THE PAPER. 103 
 
 should not be used, on account of its excessive brilliancy ; 
 but rather plain salted paper, or paper prepared by float- 
 ing on a mixture of equal volumes of albumen and 
 water containing 4 per cent, of salt. Albumenised paper 
 should be preserved in tin or zinc boxes, closed from con- 
 tact with a damp atmosphere, for if it absorbs moisture 
 it becomes rapidly changed, especially in summer time. 
 Whether the amateur prepares his own paper, or whether 
 he buys it, there are always some bad sheets. Sometimes 
 there are great lines arising from the draining of the 
 albumen towards one point, sometimes the gloss is greater 
 at one place than another, without the reason being very 
 obvious. 
 
 2. Sensitising the Paper. 
 
 This operation should be performed in the dark, or at 
 all events in a moderate light. Daylight does not act by 
 any means so energetically on positive paper as on collo- 
 dion; nevertheless, it is advisable to have a room specially 
 arranged for the purpose. 
 
 To this end the windows should be furnished with 
 yellow blinds or frames, which will admit a large body 
 of light, having no action on the prepared paper. 
 
 Paper is sensitised by floating it for three or four 
 minutes on a silver-bath of 20 per cent. 
 
 . Water 20 ounces. 
 
 Kecrystallised Nitrate of Silver 4 ,, 
 
 This solution is poured into a perfectly clean dish, and 
 the paper floated thereon, in the manner shown at Fig. 82. 
 
 If the proportion of nitrate of silver be much reduced 
 the proofs will be wanting in vigour ; from which circum- 
 stance, as often as 100 sheets of paper, 9 inches by 7, 
 have been sensitised, half an ounce of nitrate of silver 
 should be added to the bath. 
 
 In order to avoid soiling the fingers, and also the stains 
 which would be produced by the contact of the clips, it 
 is best to turn up a corner of the sheet (Fig. 86), which 
 prevents its absorbing any of the nitrate of silver, and 
 may, therefore, be taken hold of for hanging up the sheet. 
 Instead of hanging the sheets of paper by hooks (Fig. 
 87), they can be more conveniently suspended by some 
 
104: PHOTOGRAPHIC PROCESSES. 
 
 little articles, supplied with india-rubber springs, known as 
 American Clips (Fig. 88). 
 
 It is only necessary to press on the ends of these clips in 
 order to open them, and to withdraw the pressure after 
 
 Fig. 87. 
 
 inserting the paper, which is then held with the greatest 
 tenacity. Figs. 83 and 84: show how these improved clips 
 are used. 
 
 Small pieces of white blotting-paper should be attached 
 to the corners of the sheet from which the 
 solution is draining, and the drops of nitrate of 
 silver may be collected in test-glasses (Figs. 
 83 and 84), although the drops so collected 
 serve only for transformation into chloride of 
 silver. 
 
 The dry sensitised sheets shoul d be used 
 within a day or two after preparation, unless pre- 
 served in a box with chloride of calcium, to be 
 presently described. 
 
 The silver-bath may, of course, be used until it is 
 exhausted, remembering always to add the half ounce of 
 nitrate of silver for every 100 sheets 9 inches by 7, as 
 before mentioned. It must, however, be filtered every 
 time it is desired to sensitise a fresh batch of paper. 
 
 A special bath should be used for albumenised paper, 
 to which should be added one -fortieth of its weight of 
 kaolin, which should always be kept at the bottom of the 
 bottle, shaking it up from time to time, and regularly 
 allowing it to settle. This kaolin maintains the bath in a 
 colourless condition, for without it the solution would 
 acquire a deep yellow colour which would be communi- 
 cated to the proofs. 
 
 When a number of sheets have been sensitised, they 
 
SENSITISING THE PAPER. 
 
 105 
 
 are placed in portfolios, one on the other, handling them 
 only by the edges, in order to avoid contact of the fingers, 
 which produces stains. They should be used within three 
 days. 
 
 Fig. 89. Apparatus for preserving Sensitised Paper?. 
 
 If it be desired to preserve sensitised paper for some 
 months, an apparatus must be employed consisting of a 
 box with an air-tight cover, and containing some dried 
 chloride of calcium. Figs. 89 and 90 represent two forms 
 of the apparatus. Fig. 89 consists of a square zinc or tin 
 box, about six inches deep, furnished with 
 a false bottom, on the top of which is 
 placed the sensitised paper, and under- 
 neath a metal or porcelain basin filled with 
 pieces of dried chloride of calcium) the 
 whole is closed by a well-fitting lid, which 
 can be rendered air-tight by pasting a 
 strip of paper around the joining. 
 
 The other form, Fig. 90, is a very con- 
 venient, one for travelling. The outer 
 cylinder B and cover A are made of zinc 
 or tin plate ; the inner core E D is formed 
 of canvas or metal gauze, and is filled with 
 pieces of dried chloride of calcium. A 
 sheet of blotting-paper is first rolled round 
 this core, and afterwards the sheets of f 
 sensitised paper; it is then put into the l 
 cylinder, the lid adjusted, and a band of Fi ff- 9 
 vulcanised india-rubber placed over the joining, as shown 
 at 0, which renders the whole air-tight. 
 
 Whenever anv of the sheets of paper are required to 
 F 3 
 
PHOTOGRAPHIC PROCESSES. 
 
 be taken from either form of apparatus, it should be closed 
 again as quickly as possible, because the chloride of calcium 
 very rapidly attracts moisture from the air; from which 
 circumstance its peculiar action of keeping perfectly dry 
 the air in the interior of the boxes depends. 
 
 When the chloride of calcium has been some time in 
 use, it becomes covered with moisture, and eventually 
 converted into a liquid, and its action destroyed. So soon 
 as any moisture is perceived, it ought to be placed in a 
 moderately hot oven, in a porcelain or iron vessel, until 
 perfectly dry, when its properties will be entirely restored. 
 Thus the same quantity of chloride of calcium can be used 
 over and over again for any length of time required. 
 
 3. Exposure of the Prepared Paper to Light. 
 
 A printing frame is procured, furnished with screws 
 
 for large plates, and with 
 springs for small nega- 
 tives. The instrument 
 (Fig. 91) consists of a 
 simple wooden frame, 
 at the bottom of which 
 is a strong piece of 
 plate glass, which should 
 be always well cleaned 
 - on both sides before 
 I using. The negative is 
 placed on this glass with 
 the plain side down- 
 wards, while the sensitised side of the paper is brought 
 into contact with the collodion film, which is, of course, 
 uppermost. 
 
 In order to maintain perfect contact between the sen- 
 sitised paper and the negative, the printing-frame is fur- 
 nished with a hinged board lined with cloth or felt, and 
 kept in its place by transverse bars with springs or screws. 
 If it be desired to examine the progress of the printing,, 
 one of the transverse bars is removed, the hinged board 
 is opened, and one half of the paper bent back, as shown 
 in Fig. 92. This operation should, of course, not be per- 
 formed in the direct sun -light, but in the shade. 
 
 Fig. 91. Printing Frame. 
 
EXPOSURE OF THE PREPARED PAPER. 
 
 107 
 
 A consideration of the following list of successive 
 changes, through which the paper passes, will guide the 
 operator in judging when a print has been sufficiently 
 exposed. 
 
 'Fig. 92. How t.i examine the Acli^n of Ligh , on the Paper. 
 
 The paper turns 
 
 1. Very pale blue. 
 
 2. Pale blue. 
 
 3. Clear bluish purple. 
 
 4. Deep purple. 
 
 5. Black. 
 
 6. Metallic greyish black. 
 
 7. Olive, or greenish bronze. 
 
 It is not sufficient that the picture when examined, as 
 shown in Fig. 92, should seem to be printed deep enough, 
 because the fixing agent removes a great deal of the depth 
 of the colour; on this account, and in order that the 
 finished print should possess the proper depth of tone, it 
 
108 PHOTOGRAPHIC PROCESSES. 
 
 is necessary that the tint imparted by exposure in the 
 printing frame should be much deeper than is required 
 for the finished picture. 
 
 The time, then, for withdrawing the paper from the 
 action of the sun or light, depends solely on the method 
 of fixing, and is best learned by experience. 
 
 Pressure -frames should be made with the greatest care, 
 for if, for example, the back for pressing the paper against 
 the glass should not be quite flat, the paper will in some 
 places be away from the negative, while in other parts 
 the contact will be complete, and the resulting positive- 
 image will bear evidence of unequal sharpness, thus 
 marring the beauty of the picture. 
 
 Professional photographers, who generally have a great 
 many negatives to print from, arrange the pressure -frames 
 on a framework, so constructed as to admit of the angle 
 of inclination being altered in such a way as to receive 
 the solar rays perpendicularly. 
 
 The more vigorous and fully developed the negative, 
 the more brilliant and satisfactory is the resulting positive 
 proof. But if the negative be a weak one, it is possible, 
 notwithstanding, to produce a passable print from it by 
 prolonging the action of the 
 solar rays. To this end the 
 frame is exposed not to the 
 direct rays of the sun, but to 
 diffused daylight. Or better 
 still, the printing frame may 
 be covered, as shown in Fig. 
 94:, by a light frame, upon 
 
 which is stretched a piece of 
 
 fig. 03. v^nette G:asscs for Gia~ thick white paper. When it 
 is desired to produce portraits 
 
 with a white background, glasses with yellow borders 
 and white centres are employed, called vignette glasses, 
 as shown in Fig. 93. 
 
 It will be understood that the yellow portion of these 
 glasses prevents the passage of the chemical rays, and as 
 the action of light on the chloride of silver takes place 
 only through the colourless portion of the glass, that is to 
 say, in the centre, it follows that from an ordinary negative 
 a picture may be obtained with a white background. 
 
EXPOSURE OF THE PREPARED PAPER. 
 
 109 
 
 When the background of a negative is not sufficiently 
 developed, or is defective through any other cause, it be- 
 comes very difficult to remedy. Some persons paint in the 
 background, others cut out the figure from a positive print 
 and paste the matrix, or background portion, on the 
 
 iij. 94. Movcable Framework for Printing Positives. 
 
 negative ; but in either case the outline of the picture is 
 always hard and disagreeable. A better plan is to cover 
 the pressure frame with the vignette glass, Fig. 93, 
 taking care, of course, to place the oval in such a posi- 
 tion that only the bust shall be printed, while the defective 
 background is as much as possible masked. 
 
 The following is the method adopted when'it is desired 
 to produce the effect of clouds in a proof ; firstly, a negative 
 is taken with the ordinary exposure, in w r hich the sky 
 will be perfectly black; secondly, another negative is taken 
 
110 PHOTOGRAPHIC PROCESSES. 
 
 with such a short exposure that nothing appears when the 
 developing solution is poured on but the sky. With this 
 short exposure the effect of clouds is very successfully 
 obtained. 
 
 A positive being printed from the first negative will have, 
 of course, a white sky ; this being placed under the second, 
 or cloud negative, the foreground of which is covered with 
 cotton wool in such a way that light can pass only through 
 that portion of the glass bearing the image of the clouds. 
 The outline of the objects in the landscape is covered 
 with cotton wool, the fibres of which have been well 
 pulled out, in order that the hardness which would be 
 otherwise produced may be moderated and toned down. 
 An exposure of a few minutes will be found sufficient to 
 produce the desired effect. 
 
 To produce a similar effect artificially is even still more 
 easy. In taking the negative it is arranged in the expo- 
 sure that the sky shall not be too deep, and the desired 
 cloud effects are painted, not on the film, but on the 
 other side of the glass. It should be remembered, how- 
 ever, that the effect produced in the positive proof will 
 be the reverse of what is painted on the glass. 
 
 A recently varnished negative should not be imme- 
 diately printed from under the direct rays of the sun, for 
 however good the varnish employed may be, it invariably 
 sticks a little when freshly applied. Instead of exposing 
 to direct sunlight, use diffused daylight, or better still, 
 cover the pressure -frame with a case or covering of white 
 paper. 
 
 Paper should be made perfectly dry after sensitising, 
 and before being placed in contact with the negative, 
 otherwise the moisture in the fibres of the paper will be 
 volatilised by the sun's heat, and condense on the negative, 
 which will soon become blackened by the nitrate of silver 
 of the paper. When this is discovered in time, the spots 
 so produced may be removed by cyanide of potassium ; 
 the operation, however, requires great dexterity and 
 judgment. 
 
 Negatives should never be allowed to remain all night 
 in contact with paper at all damp, as the depression of 
 temperature induces a condensation of moisture on the 
 surface of the glass, and brings about the same untoward 
 
TONING AND FIXING THE PRINT. Ill 
 
 result as occurs under the circumstances detailed in the 
 preceding paragraph. 
 
 Unusual precautions are necessary in the use of albu- 
 menised paper, which easily sticks to the negative, and 
 shows stains wherever it is touched. It should be handled 
 only by the extreme edges. 
 
 It is very important that the woodwork of pressure - 
 frames should be well put together, so that no warping 
 shall occur through changes of temperature or differences 
 in the hygrometric condition of the atmosphere ; other- 
 wise the prints will not be equally sharp over the entire 
 surface, owing to the unequal contact between the paper 
 and glass induced by the warping. Moreover, the nega- 
 tives are very likely to become cracked from the same 
 cause. 
 
 A great many sheets of positive paper may be prepared 
 at a time, on the sole condition of keeping them in a box 
 with chloride of calcium, as described at page 105. This 
 box, however, ought not to be opened oftener than is abso- 
 lutely necessary, but enough paper should be withdrawn 
 at one time to serve for two days' consumption. 
 
 Before placing the negative in the pressure-frame, the 
 plate -glass should be carefully wiped, in order to avoid 
 the accumulation of dust on the proof. 
 
 When the paper is placed in the frame the screws must 
 be tightly adjusted, so as to secure it against the slightest 
 movement when the hinged back is opened to examine 
 the progress of the printing. 
 
 The frame itself should be a little larger than the 
 hinged back, in order that the latter may open without 
 difficulty. If it be so tight as to require on effort to 
 open it, there will almost invariably occur a displacement 
 of the negative, and a consequent doubling of the outline 
 in the proof. 
 
 4. Toning and Fixing the Print. 
 
 The process of toning is employed to impart a pleasing 
 tint to the proof, and the object of fixing is to remove 
 the unaltered chloride of silver by immersion in a solu- 
 tion of hyposulphite of soda. 
 
 In order to avoid constantly touching the proof during 
 
112 PHOTOGRAPHIC PROCESSES. 
 
 these operations, horn or boxwood forceps are employed, 
 or glass rods bent as shown in Figs. 95 and 96. 
 
 Fig. 95. 
 
 Many formulae have been given for toning and fixing 
 the prints, in some of which 
 the two operations are con- 
 ducted simultaneously ; in 
 others the fixing is done be- 
 fore the toning, and in a third 
 the toning is effected before 
 the fixing. 
 
 The latter process, how- 
 Fig ' 96 * ever, is the one by which the 
 
 best results and the greatest permanency are obtained. 
 It consists of four operations : 1. Washing the print, to 
 remove the free nitrate of silver adhering to the surface, 
 and which has remained unchanged by light. 2. Toning 
 in a weak solution of chloride of gold, to which a small 
 quantity of carbonate of soda has been added. 3. 
 Washing again to get rid of the chloride of gold. 4. 
 Fixing in a solution of hyposulphite of soda. 
 
 The chloride of calcium box (Fig. 89) serves as well 
 for the preservation of proofs which have been exposed 
 to light as for sensitised paper. As it is desirable to fix 
 a large number of proofs at one time, it is recommended 
 that the operator should at the outset provide himself 
 with three, at least, of the chloride of calcium boxes ; 
 one for preserving the white chloride, another for the 
 paper ready for immediate use, and the third for paper 
 which has been exposed under a negative. 
 
 The room set apart for the production of positive 
 proofs should be on the ground-floor, and the panes of 
 glass darkened with yellow paper ; it should be furnished 
 with several large wooden troughs for washing, and an 
 assortment of porcelain or brown stoneware trays for 
 
TONING AND FIXING THE PRINT. 113 
 
 hyposulphite solutions, &c. There should also be an 
 abundant supply of water. 9 
 
 The proofs being taken either from the pressure -frame 
 or the chloride of calcium box, are plunged one after the 
 other into a porcelain pan containing rain-water, which 
 is changed for every hundred prints. This bath should 
 be at least one foot deep. 
 
 By far the greater quantity of the nitrate of silver 
 withdrawn from the sensitising bath still remains on the 
 surface of the paper after exposure to light. The bath 
 of rain-water dissolves the nitrate of silver, and when 
 the water is thoroughly charged therewith, it may be 
 treated as described at page 75, by throwing in an excess 
 of common salt, which produces a precipitate of cholride 
 of silver. 
 
 There should not be more than ten prints washed at a 
 time in this bath, and special care should be taken to 
 prevent any hyposulphite of soda from falling therein, 
 on which account the bath may be advantageously covered 
 with a plate of glass, and the prints touched only with 
 boxwood forceps. 
 
 When the prints have been for about ten minutes in 
 the water, they are taken out one at a time and immersed 
 in the toning-bath. To prepare the toning-bath, make 
 the two following standard solutions : 
 
 .- - f Bicarbonate Soda 2 drachms. 
 
 ' (Water 32 ounces. 
 
 _- 2 f Chloride Gold 30 grains. 
 
 (Distilled Water 32 ounces. 
 
 Take one quart of water and dissolve in it two drachms 
 of common salt; then add one ounce of solution No. 1 
 and one ounce of No. 2. This toning-bath should be 
 kept about ten minutes before being used. 
 
 The first prints which are immersed in the bath after 
 the addition of the chloride of gold tone rapidly ; but in 
 proportion as the gold is taken up, the toning proceeds 
 more slowly, when more of solution No. 2 will have to be 
 added. To accelerate the toning in winter, the solution 
 may be slightly warmed by setting the dish on a sheet 
 of plate iron heated with a spirit lamp. 
 
 The chloride of sodium or common salt is added to the 
 
114 PHOTOGRAPHIC PROCESSES. 
 
 bath to transform into chloride the nitrate of silver which 
 has not been washed out, and which would otherwise 
 decompose the Chloride of gold. 
 
 The prints being put into the toning -bath will first 
 become red, and will then pass successively through all 
 the intermediate tints between red and black. The toning 
 can be stopped at any stage by immersing the print in a 
 tray of clean water, which should be kept at hand for the 
 purpose. 
 
 The real colour is only seen after immersion in the 
 hyposulphite fixing solution, and it is at this stage only 
 that the operator can judge to what tint he should tone 
 his pictures, in order that they should finally possess the 
 desired colour. As a general rule the bluish black 
 changes to a pure black in the hyposulphite ; less toning 
 than is required to give the bluish black produces prints 
 more or less brown ; if the toning is pushed further than 
 the bluish black, the prints will be ashy coloured and flat 
 when dry. 
 
 Prints which have to be toned black must be printed 
 deeper than those which have to be toned purple or 
 brown, for the toning-bath has also a bleaching action, 
 
 Prints on albumenised paper require for toning a larger 
 quantity of gold than prints on ordinary salted paper. 
 
 The toning-bath may be used over and over again, by 
 adding from time to time more gold and bicarbonate of 
 soda; but, as hyposulphite of soda is liable to be acci- 
 dentally introduced into it, it is advisable, where a large 
 number of prints are produced, to make a new one every 
 day. 
 
 In order to judge of the colour of the proof it should 
 be withdrawn from the gold-bath by means of a boxwood 
 forceps, as, on account of the yellow colour of the bath, 
 it is difficult to form an accurate estimate while the print 
 remains therein. The same remark may be applied to 
 the colour of the panes of glass in the printing room. It 
 has been said that they should be covered with yellow 
 paper, but this applies, of course, only to those panes 
 which illuminate that part of the room in which the 
 prints are either withdrawn from the pressure -frame or 
 placed therein, or where the first washing with plain 
 water takes place. All the other operations may be 
 
TONING AND FIXING THE PRINT. 115 
 
 safely conducted by daylight, although it will be found 
 quite as well to preserve the whole of the workshop from 
 the direct action of the solar rays by means of blinds. 
 
 The prints, as soon as they are taken out of the toning- 
 bath, are immersed in water ; they are then washed 
 several times, and put into the fixing-bath, which is 
 composed as follows : 
 
 Hyposulphite of Soda 8 ounces. 
 
 Water 1 pint. 
 
 The fixing will generally require from ten to fifteen 
 minutes ; but it is easy to understand that the longer the 
 bath has been in use, the more will its capacity for dis- 
 solving chloride of silver become exhausted, and the 
 longer will the print require immersion, so that, one 
 pound of hyposulphite of soda will not fix more than one 
 hundred prints, 8J in. X 6 Jin.; but as this salt is very 
 cheap, to use it liberally will make but a fractional in- 
 crease in the cost of the prints. 
 
 The hyposulphite bath should, then, be often changed, 
 and when out of use it may be kept for the purpose of 
 extracting the silver. 
 
 The proof which comes from the last bath is now 
 rinsed in a wooden trough filled with water, to remove 
 the excess of adherent hyposulphite ; then allowed to 
 soak for two hours in a second trough, and for three 
 hours in a third. There should be an extra trough or 
 dish for every twenty-five prints of 8J in. X 6| in. 
 When the prints are allowed to remain longer in the 
 water than is specified above, they lose their beautiful 
 colour and become yellow. 
 
 It is sometimes desired to finish the washing of a print 
 somewhat hurriedly, and yet to ensure the complete 
 removal of every trace of hyposulphite of soda; when 
 this is the case, the proof is placed on a glass plate of 
 suitable size, and moved about under a stream of water 
 from a tap falling from a height of about six feet. The 
 motion imparted to the glass should be so regulated as 
 to allow the water to fall on every part of the proof in 
 succession, without tearing it or causing its separation 
 from the glass. Five minutes of this energetic washing 
 removes the hyposulphite more effectually than five hours 
 
116 PHOTOGRAPHIC PROCESSES. 
 
 soaking in the troughs of water, although it is obvious 
 that the consumption of water is much greater. A badly 
 fixed or imperfectly washed print undergoes spontaneous 
 alteration after a few weeks. 
 
 The following may be received as practical rules to 
 avoid the fading of prints. 
 
 As silver forms, with hyposulphite of soda, a double 
 salt, slightly soluble in a feeble excess of hyposulphite 
 of soda, but on the contrary very soluble in a con- 
 centrated solution, and as this double hyposulphite 
 of silver and soda decomposes with great facility, it 
 is very important that concentrated solutions should be 
 used, in order that the double salt shall be dissolved as 
 soon as formed. 
 
 A bath such as that of which the formula has been 
 given, must not be used too long, and for the same reason 
 too many proofs must not be immersed therein at one 
 time, especially if there be not sufficient space between 
 each proof to allow the bath to exert its full solvent 
 action. 
 
 All the formula3 which prescribe the addition of an 
 alkali or an acid to the bath should be unhesitatingly re- 
 jected. The chloride of gold of commerce is sometimes 
 very acid, in which case it may be replaced, if desired, by 
 a white salt known by the name of Sel d'Or de Fordos 
 et Gelis ; this must be very much diluted before mixing 
 with the hyposulphite of soda. 
 
 If the proof, through insufficient washing, contains 
 hyposulphite of soda, it will have, when dry, a sweet 
 taste, and will fade in a very short time. 
 
 Finally, all fermented or fermentable substances for 
 mounting photographs, should be rejected. Nothing but 
 recently prepared starch-paste should be used, and the 
 proof should be allowed to dry very rapidly when mounted, 
 in order that no acid principles may be developed by 
 fermentation. 
 
 In rainy climates in winter in England, for ex-ample 
 it is sometimes necessary to expose the paper for a 
 whole day to the light before a positive can be obtained. 
 Albumenised paper being much more rapid than simple 
 salted paper, will therefore be preferred, although even 
 this will sometimes fail to produce a positive in a reason- 
 
TONING AND FIXING THE PRINT. 117 
 
 able time, in which case recourse may be had to the follow- 
 ing expedient. 
 
 Plain paper being cut to the proper dimensions, and the 
 reverse side marked with a pencil, is allowed to float 
 for about one minute on a bath composed of 300 grains 
 of iodide of potassium dissolved in 35 ounces of water. 
 This bath serves until it is exhausted, and the paper when 
 dry and placed in a portfolio will keep a long time. The 
 paper so prepared is rendered sensitive to light by floating 
 (in the dark, of course) on a bath of nitrate of silver for 
 one minute. The bath is composed of 
 
 Water 3i ounces. 
 
 Fused Nitrate Silver 30: grains, 
 
 Glacial Acetic Acid 300 
 
 The paper is withdrawn from the bath, well drained, and 
 rapidly dried between folds of blotting-paper, in order to 
 remove the excess of -solution, and prevent its touching 
 the back of the paper. This operation is repeated with 
 a second and even a third sheet of blotting-paper. It is 
 necessary that the sensitised sheet should be damp, but 
 not to such a degree as to stain the negative, upon which 
 it should be pressed very lightly. 
 
 The exposure to diffused daylight varies between five 
 and fifteen seconds ; a long exposure yields a flat picture, 
 deficient in brilliancy in a short one the sky only 
 appears. 
 
 The paper is carefully removed from the negative, and 
 placed on a sheet of glass with the sensitised side upper- 
 most. A solution is then made of 15 grains of gallic 
 acid in 35 ounces of warm water, to which is added 3| 
 drachms of glacial acetic acid. This is filtered and 
 spread very quickly by means of a brush or glass rod over 
 the sensitised side of the sheet. The image appears very 
 rapidly, and as soon as the desired effect is arrived at, 
 the paper is plunged into water to arrest the action of 
 the developer. 
 
 After washing, it is toned with chloride of gold, as 
 described at page 113, and it is then washed for two hours 
 in a large trough of water. 
 
118 PHOTOGRAPHIC PROCESSES. 
 
 5. Mounting the Proofs. 
 
 Whatever process may have been adopted in the pro- 
 duction of the positive print, it has finally to be pasted 
 on Bristol board, and rolled. 
 
 Nothing is more simple than the mounting of a proof. 
 It is cut into any suitable or desired form, and the back 
 covered with starch-paste. It is then spread on the 
 Bristol board, a piece of blotting-paper laid over it, and 
 the whole rubbed with the hand in every direction, in 
 order to ensure complete contact between the print and 
 the board. This being done, it is allowed to dry in the 
 air, and subsequently rolled in a lithographic or other 
 press, by which it acquires a finishing gloss, which is 
 entirely absent in unrolled prints. 
 
 Poirier's press, represented in Fig. 97, is very applic- 
 able for this purpose. It is composed of a steel roller, E, 
 the axle blocks of which are moveable in a vertical direc- 
 tion ; double levers are employed to make the necessary 
 adjustment, and the power is applied at & b. It is suffi- 
 cient to move one only of these heads in order to move 
 the other, there being an arrangement of cog-wheels 
 for this purpose. However, for delicate adjustments, 
 the power is best applied to each screw-head separately, 
 which, in turning, depresses two screws attached to the 
 axle -blocks, these latter sliding between two edges of 
 cast-iron. 
 
 The other part of the apparatus consists of a plate of 
 planed polished steel, a a, or of a very flat lithographic 
 stone, which receives its backward and forward motion 
 from a toothed wheel, moved by a still smaller one, which 
 in its turn is moved by a long lever or handle. 
 
 Upon this steel plate two very smooth and specially 
 prepared cards are placed, between which the proof to be 
 rolled is laid. The screws being adjusted, and the motion 
 imparted, the steel plate moves on, turning the cylinder 
 at the same time. An enormolis pressure is thus brought 
 to bear uniformly over the whole surface of the card, and 
 after two or three movements to and fro, the screws 6 b 
 are slightly tightened, and the rolling repeated. 
 
 The proof thus becomes pressed into the cardboard, 
 
TONING AND FIXING THE PRINT. 
 
 119 
 
 and acquires a splendid gloss. To mount stereoscopic 
 views and cartes de visite, they should be cut by means of 
 a steel or glass mould and a good knife. 
 
 It is a good plan to paste a great many proofs on one 
 card, in order to effect the glazing by one operation. 
 
 A beautiful gloss can be imparted to stereoscopic and 
 carte de visite proofs by varnishing them. This varnish is 
 made as follows : One ounce of white lac is dissolved 
 
 Fig. 97. Rolling Press. 
 
 in ten ounces of warm alcohol, and after allowing the 
 bottle to stand for several weeks, the clear portion is 
 decanted for use. 
 
 This varnish is then applied in a similar manner to 
 that adopted by French polishers in polishing cabinet 
 
120 PHOTOGRAPHIC PROCESSES. 
 
 work ; it has been introduced into commerce under the 
 name of Crystal Enamel. 
 
 The picture having been mounted, is sized with a warm 
 solution made by dissolving 10 grains of Swinborne's 
 gelatine in 1 ounce of water, and either hot-pressed or 
 burnished with an agate burnisher. It is then coated 
 with the crystal enamel, applied in the following manner : 
 A tampion of cotton -wool saturated with the liquid is 
 wrapped in a piece of clean white calico rag, the outer 
 surface of which is touched with a drop or two of linseed 
 oil : this is gently and evenly applied with a circular 
 motion over the whole surface to be enamelled, until the 
 picture becomes brilliant. It is, lastly, finished off by 
 applying, in the same manner, alcohol and linseed oil. 
 
NOTES. 
 
 NOTE 1 (page 4). 
 APPEARANCE OF NEGATIVES. 
 
 The difference of the reverse appearance of an ordinary negative on 
 glass or paper, and the direct one exhibited by a metal plate, is simply 
 apparent and not real, and arises solely from the mirror-like appearance 
 in those parts of the silver plate not acted on by light. And this explains 
 the reason why it is necessary to give to these '(daguerreotype) pictures a 
 particular position in relation to the angle at which the light strikes 
 them. At other angles, when, for example, the light is directly reflected 
 from the surface of the metal, the image appears as a negative. 
 
 NOTE 2 (page 16). 
 DISTILLATION OF ETHER. 
 
 The object aimed at in the distillation of a liquid is the separation of 
 any solid substance which it holds in solution, or any liquid of a dif- 
 ferent constitution with which it may be mixed. In the instance under 
 consideration, it is necessary to separate the ether, not only from the 
 chloride of calcium upon which it has been dried, but also from the 
 alcohol and water which it contains. 
 
 The boiling point of ether being about 96 Fahr., and of alcohol ] 74 
 Fahr., and water 212 Fahr., it follows, that if a mixture of the three be 
 submitted to the action of heat, the ether will be almost completely 
 volatilised before any sensible evaporation of the alcohol or water has 
 taken place. A tube thermometer, having its stem passed through the 
 cork, and its bulb so arranged as not to come into contact with the 
 liquid, will indicate a temperature of about 96, rising higher in propor- 
 tion as more alcohol and water become evaporated. To secure pure 
 ether, the temperature should not rise higher than 104. 
 
 G 
 
122 PHOTOGRAPHIC PROCESSES. 
 
 The first portions which come over should not be used, as they gene- 
 rally serve only to cleau the condensing tube, and, consequently, contain 
 impurities. From two pints of ether, therefore, the first ounce and a 
 half which comes over should be rejected. 
 
 NOTE 3 (page 18). 
 PREPARATION OF PYROXYLINE. 
 
 The cotton should be chosen free from defects and any contaminating 
 organic matter. A mixture is then made of 
 
 Sulphuric Acid (Sp. Gr. 1*8) 38 fluid ounces. 
 Nitric Acid (Sp. Gr. T4) 19 do, do. 
 
 This is stirred with a glass rod, and if examined by a thermometer will 
 be found to indicate a temperature of 176 Fahr. ; the operator should 
 therefore wait until it cools down to 140 Fahr. before plunging in the 
 cotton. 
 
 The quantity of cotton to use is about 1,050 grains, which is added to 
 the acids, about one-fourth or one-fifth part at a time, squeezing it with 
 the glass rods in order to force out the air imprisoned between the fibres. 
 When all the cotton is immersed, the containing vessel is covered with 
 a plate to keep in the nitrous vapours, and at the end of ten minutes the 
 cotton is withdrawn, and copiously drenched with water, as before 
 described. The pyroxyline thus obtained is less soluble in ether and 
 alcohol than that obtained by the ordinary method ; but it is especially 
 useful when great tenacity of film is required. 
 
 NOTE 4 (page 19). 
 EMPLOYMENT OF THE IODIDES AND BROMIDES. 
 
 Besides iodide and bromide of cadmium, a great number of other 
 iodides have been used, among which may be mentioned those of potas- 
 sium, sodium, ammonium, zinc, &c. 
 
 Many photographers confine themselves to the use of the iodides 
 of potassium and ammonium, but lately iodide of cadmium has come 
 generally into use. 
 
 More recently has been proposed, especially for copying pictures, a 
 collodion, containing iodide, bromide, and chloride of ethylamine. The 
 following is the formula which has given the best results : 
 
NOTES. 123 
 
 Alcohol 1'i ounce. 
 
 Ether 2'f 
 
 Pyroxyline 15 grains. 
 
 Iodide of Ethylamine 1'2 ,, 
 
 Bromide ditto 04 ,, 
 
 Chloride ditto 0'2 
 
 Although iodide of ethylamine is not found in commerce, it is very 
 easy to prepare. It is an organic iodide, containing nitrogen, and the 
 elements of alcohol, but is nevertheless more stable than iodine of ammo- 
 nium, and yields pictures of remarkable delicacy. 
 
 NOTE 5 (page 34). 
 NITRATE OF SILVER STAINS. 
 
 Nitrate of silver is reduced by contact with all organic substances, and 
 as finely-divided metallic silver is black, it follows that this substance 
 blackens everything it touches, as every photographer knows. Many 
 methods have been proposed for the removal of these spots. The follow- 
 ing is the best. 
 
 The hands become inevitably stained while conducting the manipula- 
 tions involved in the sensitising and development of the plates, but it is 
 not until some hours have elapsed that the stains, at first scarcely visible, 
 deepen to any great extent; and it is only when a great number of 
 proofs have been taken that the method about to be proposed is required 
 or advisable. 
 
 It consists simply in well washing the hands in a saturated solution 
 of hyposulphite of soda, kept expressly for that purpose. Two or three 
 minutes' contact are found sufficient to remove every trace of the stain. 
 Instead of hyposulphite of soda, iodide of potassium may be used in the 
 same way. After the hyposulphite, it is advisable to wash the hands 
 with soap, and with powdered and sifted pumice stone. 
 
 If the stains are very old, it is better to allow them to wear away by 
 time ; however, as they sometimes are obliged to be removed, in that 
 case, a mixture of cyanide of potassium and iodine applied to the fingers 
 by a brush, or otherwise, will, if aided by the use of a lump of pumice 
 stone, rapidly restore the hands to their normal condition, after which 
 they should be well rinsed with plenty of water. 
 
 In the use of this latter re-agent for the purpose indicated, it is 
 important to remember that cyanide of potassium is an energetic poison, 
 which acts not only internally, but externally, by absorption ; so that it 
 should never be used when there is the slightest wound or scratch upon 
 the hands. 
 
 If this advice be neglected, serious results may follow. It is also 
 advisable that this mixture should only be prepared at the time of using 
 it, and that every vessel which has contained it should be carefully 
 cleaned. 
 
 G 2 
 
124 PHOTOGRAPHIC PROCESSES. 
 
 NOTE 6 (page 35). 
 PREPARATION OF THE NITRATE OF SILVER BATH. 
 
 Into a graduated glass is placed 1,200 grains of nitrate of silver, upon 
 which ia poured 7 ounces of distilled water. When the nitrate is all dis- 
 solved, which can be hastened by well stirring with a glass rod, there is 
 to be added 3 drams of an alcoholic solution of iodide of cadmium, con- 
 taining 10 grains to the ounce ; a yellow precipitate is immediately pro- 
 duced. The whole is well agitated together, and left to itself for about 
 one quarter of an hour; more distilled water is then added to make up 
 the quantity of 35 ounces ; it is then filtered, and is ready for use. 
 
 NOTE 7 (page 55). 
 PREPARATION OF PYROGALLIC ACID. 
 
 This substance was discovered by Scheele, who supposed it to be sub- 
 limed gallic acid. It contains the elements of gallic acid, minus those 
 of carbonic acid. 
 
 Dry and pure pyrogallic acid has the form of lamellar needles, or 
 elongated plates, which are soluble in 2J parts of water at ordinary 
 temperature, and a little less soluble in ether and alcohol. It has a very 
 bitter taste, and when quite pure, does not redden tincture of litmus. A 
 solution of the pure acid will keep, so to speak, indefinitely, especially if, 
 as is the case when it is prepared for photographic use, an acid be added. 
 
 It is of the highest importance to keep pyrogallic acid in stoppered 
 bottles, in the dark ; since, unless this be done, it gradually turns brown, 
 through combination with the oxygen of the air, and its properties 
 injured. 
 
 Pyrogallic acid is prepared by boiling bruised nut-galls, with seven or 
 eight times their weight of water, for three or four hours, replacing the 
 water as fast as it evaporates. The whole is then thrown on a strainer, 
 and the dirty cake of nut-galls being submitted to powerful pressure, in 
 order to remove all the liquid. 
 
 The mixed liquors are then evaporated, first, by rapid ebullition, and 
 afterwards more gently, until they acquire the consistence of an extract, 
 which extract is rendered perfectly dessicated by careful drying in a 
 stove. 
 
 This product is then heated for ten or twelve hours in a flat iron 
 vessel, over the top of which is stretched a piece of perforated paper, the 
 whole being covered by a conical paper cap. The vessel is placed on a 
 sand-bath, and the temperature, which should not rise higher than 420 
 Fahr., is indicated by one, or, still better, two thermometers. And this 
 is the most delicate part of the operation. If the heat be insufficient, no 
 result is obtained, and if it be too much heated, another product is 
 obtained which contains no pyrogallic acid. 
 
 Operating in this way, 100 parts of dry extract yield 5 parts of pure 
 pyrogallic acid, and at a more advanced stage of the sublimation, 5 parts 
 of impure acid, which may be purified by resublimation. 
 
NOTES. 125 
 
 NOTE 8 (page 47). 
 PHOTOGRAPHIC OPTICS. 
 
 The reader will readily understand that it is by no means easy in BO 
 limited a work as the present to give a clear idea of photographic optics ; 
 the observations to be made will therefore be confined to demonstrations 
 of the fundamental principles only of the most advanced of the sciences. 
 
 The ultimate constitution or essence of light is entirely unknown. 
 Newton entertained the idea that luminous bodies threw out in all direc- 
 tions exceedingly minute corpuscles, which, on coming into contact with 
 the optic nerve, produced a certain effect, which has been distinguished 
 by the term " luminous effect." It has, however, been since proved that 
 the hypothesis of Newton does not accord with facts, and the view most 
 generally entertained is to the effect, that there exists in space, per- 
 meating our atmosphere and all existing bodies, a luminous ether of 
 extreme tenuity, to which luminous bodies have the property of com- 
 municating a vibration similar to that which takes place when a spring 
 is suddenly struck ; and it is this vibration, communicated with an almost 
 inconceivable rapidity to the optic nerve, which produces the effect 
 which is called light. 
 
 It is not certainly known whether this last hypothesis is a correct one, 
 but it is certain that it adapts itself most completely to all the known 
 facts of optics, and thafcit has materially aided in the discovery of some 
 of them. 
 
 It is well known that light travels in straight lines at a rate of 240,000 
 miles in a second of time. 
 
 Reflection of light is that effect which takes place when light falls on 
 a plane mirror. 
 
 The light which falls on a mirror from a luminous point is called the 
 incident ray, and that which reaches the eye from the mirror is called 
 the reflected ray; and if a perpendicular be elevated from the point 
 where these two rays meet, it will be found to make two equal angles, 
 or, in other words, the angle of incidence and the angle of reflection are 
 equal. 
 
 Reflection takes place with equal regularity from the surface of curved 
 mirrors, but the image is modified according to the character of the 
 curve, which sometimes enlarges, sometimes diminishes, sometimes re- 
 verses the image, and sometimes gives an erect image. 
 
 Refraction is that phenomenon which is shown when a stick is plunged 
 into water, by its appearing as though it was broken. It is also a well- 
 known fact, that the bottoms of rivers appear to be a great deal nearer 
 than they really are, and that in consequence great mistakes are some- 
 times made in judging of their depth ; this phenomenon also belongs to 
 refraction. In one word, refraction of light takes place whenever a ray 
 of light deviates from its original course by passing through a transpa- 
 rent body of greater or less density. 
 
 In the first place will be considered the most simple case (Fig. 98), 
 in which a ray of light R is incident on a plate of glass A, whose two 
 sides are parallel. At the point where the ray R comes into contact 
 with the glass, imagine a perpendicular line to be drawn, and then 
 
126 
 
 PHOTOGRAPHIC PROCESSES. 
 
 observe what happens to the luminous ray. (The perpendicular here 
 mentioned is distinguished by the term normal?) Experience has shown 
 that the angle R N, formed by the luminous ray and the normal ray, 
 is greater than the angle formed by the same ray in the interior of 
 the glass with the same normal ray prolonged ; but this angle is constant 
 for the same quality or character of glass. On leaving the glass the ray 
 assumes a direction parallel to the direction of the primitive ray. 
 
 It follows, then, from what has been stated, that a ray of light falling 
 on the surface of a piece of glass is refracted both on entering and 
 leaving the glass. 
 
 Figs. 99 and 100 illustrate the same fact, and also show the reflec- 
 tion of a ray from the large face of a triangular prism. 
 
 Fig. 99. 
 
 Fig. 100. 
 
 ' Fig. 98. 
 
 The study of refraction becomes more difficult when the two surfaces 
 of glass, instead of being parallel, are placed at an angle in relation to 
 each other (Fig. 101). Suppose two of these faces AC, AB, and a 
 luminous ray R0 falling on cue of the surfaces. If it were not a prism, 
 
 Fig. 101. 
 
 the ray would follow the direction R M ; but as the ray R0 is bent, as in 
 the preceding case, it approaches towards the normal in the direction o o f t 
 the angle outside the prism being greater than the angle inside. But 
 the reverse happens on the second face A B, at the point o\ and the ray 
 leaves in the direction o { R' in such a manner that the ray, first impelled 
 in the direction R M, is finally sent in the direction o f R', from which it 
 follows, that a ray of light is altered in its direction by its passage 
 through a piece of glass, the two sides of which are not parallel. 
 
NOTES. 
 
 127 
 
 Glass lenses are convex discs, ground and polished, having an exterior 
 figure of a spheroidal character. Their principal effect is, that when 
 they are exposed to the suu, the parallel rays of that luminary r r (Fig. 
 102), unite at a certain point, called the focus, all the rays converging 
 towards this point. Inversely, a luminous point being placed in the 
 focus/ of a lens A, emits rays which, on leaving the lens, are parallel 
 
 Fig. 104. 
 
 r r r r. It therefore follows, that a convex lens is in effect an assem- 
 blage of prisms, the inclination of the two faces of the glass from the 
 centre to the circumference being such that the parallel rays undergo an 
 analogous deviation, which causes them to meet at the focus. Fig. 104 
 is intended to illustrate this proposition. 
 
 In concave lenses the effect is entirely different. If solar rays r r 
 impinge on a concave lens A (Fig. 
 105), these rays, instead of uniting, 
 disperse themselves in the direction 
 r ( r ( . It is, however, usual to regard 
 the point f as the focus, resulting 
 from the ideal prolonging of the rays 
 r* r* and focal length the distance 
 A/ 
 
 105> If refraction consisted only in a 
 
 simple deviation of the rays of light, 
 it would be a comparatively simple matter, but, unfortunately, it is no 
 so ; the ray is not only bent, but decomposed into its primary colours. 
 This statement may be easily verified by examining a white object on 
 
128 
 
 PHOTOGRAPHIC PROCESSES. 
 
 a dark ground through one of the ordinary prisms used for ornamenting 
 chandeliers. The white object will appear fringed with all the colours of 
 the rainbow. 
 
 The same phenomenon occurs when a ray of light R (Fig. 101) is 
 allowed to fall on the surface of a prism. The refracted ray o' R* con- 
 sists not of one white ray, but of seven different colours. Convex lenses 
 produce the same effect. Thus, the solar rays a a falling on a convex 
 lens (Fig. 106) do not reunite in one single point, but produce at R a 
 white image, bordered above by red, and below by violet. 
 
 Fig. 106. 
 
 107. 
 
 It is possible, however, to unite two prisms (Fig. 109) in such a way 
 that the rays &' b falling thereon, shall leave it at a* a void of colour ; 
 such a combination of glasses is called an achromatic prism. These 
 prisms are composed of two kinds of glass crystal, or flint, and crown, or 
 ordinary glass. 
 
 There are not only achromatic prisms, but lenses, which yield images 
 free from colour. The curve which a particular kind of glass is to 
 receive in order that the compound lens shall be most effectually achro- 
 matised, forms the subject of a mathematical calculation. The curve is 
 then imparted by grinding the glass by hand in a suitable tool. 
 
 Fig. 108. 
 
 Fig. 109. 
 
 Fig. 110. 
 
 Fig. 111. 
 
 There are many different kinds of lenses. Fig. 108 shows three forms 
 of non-achromatic convex lenses, and Fig. 110 these same lenses achro- 
 matised. Figs. 109 and 111 concave lenses non-achromatic and 
 achromatised. 
 
 In order to explain the application of lenses in photography, it 
 
NOTES. 
 
 129 
 
 becomes necessary, in the first place, to describe a very curious pheno- 
 menon. 
 
 In looking at a well-lighted landscape, it is obvious that every point 
 of that landscape sends to us a ray of light, since, unless it were so, it 
 could not be seen at all. 
 
 Tf a hole be bored in the shutter of a perfectly dark room (Fig. 112), 
 and a sheet of white paper be placed a short distance from the aperture, it 
 will be seen that, as every point of the view emits luminous rays, a certain 
 
 Fig. 112. 
 
 number of these rays will pass through the opening into the dark chamber, 
 and being directed by the sheet of white paper, will produce thereon an 
 inverted image of the landscape. 
 
 If a convex lens be placed in the hole in the shutter, and the sheet of 
 white paper brought up to the focus of this lens, the image will be in- 
 creased so much in sharpness that it will seem quite easy to trace the 
 outline with a pencil, or, indeed, to make a finished drawing. Now, if 
 the sheet of white paper be replaced by another sheet of paper photo- 
 graphically prepared with some substances acted on by light as the 
 compound of silver, for example the image of external objects will, in 
 a longer or shorter time, be depicted thereon. 
 
 In Fig. 106 has been shown the remarkable fact, that the two 
 white rays a a become decomposed into rays of various colours ; but 
 what is still more curious is, that if the rays a a were red, they would 
 come to a focus at R ; if yellow, nearer the lens at J, and if violet, still 
 nearer at V. In one word, a lens acts equally only for light of one 
 colour, and unequally on diiferent colours. Lenses of the same form, 
 but of different glass, will also act differently on the same light ; and it 
 is precisely on this account that it becomes necessary to make a com- 
 bination of glasses of such forms that all the colours shall be equally 
 refracted and reunited in one point. 
 
 For this purpose lenses are made and placed very near to each other, 
 in some instances even united by Canada balsam, one lens, so to speak, 
 for each colour ; generally, however, the combination is confined to two 
 lenses, uniting only the two principal colours. 
 
 In the construction of photographic lenses, the relation between the 
 material, i. e. the quality and kind of glass and the form or curve 
 imparted to it is calculated in such a way as to unite into one focus the 
 yellow and the violet rays. 
 
130 
 
 PHOTOGRAPHIC PROCESSES. 
 
 Sometimes double and sometimes single objectives are employed. 
 The double objective is composed of four lenses mounted in brass. 
 Fig. 53 represents such an one, and 
 Tig. 113 the arrangement of the lenses. 
 The poiut of the arrow is directed to- 
 wards the object to be taken. This 
 ^ system of four lenses is arranged in 
 such a manner as to give a great deal 
 of light to the image, to the sacrifice, to 
 some extent, of sharpness. A single 
 Fig. 113. achromatic lens may, however, be em- 
 
 ployed which, while it gives less light, 
 wonderfully increases the delicacy of the details. 
 
 NOTE 9 (page 63). 
 SPOTS ON THE COLLODION FILM. 
 
 It is not intended to describe all the kinds of spots which are produced 
 on the collodion film, but only those which occur most frequently. 
 
 Spots are sometimes produced under the collodion film, and sometimes 
 upon the film. The first, always visible before exposure, arise generally 
 from imperfectly cleaning the plate. lu fact, the dust which remains 
 on the plate are centres of reduction for the iodide of silver constituting 
 the film, and thus form round spots. 
 
 Another source of spots arises from the presence of fatty particles in 
 the leather used for cleaning, and these produce stains such as shown at 
 page 63 (fig. 65). 
 
 In reference to spots produced on the film, they arise very often from 
 light solid bodies floating in the collodion. It is, therefore, of the highest 
 impoitance always to use a collodion which has stood some time. 
 
 It happens sometimes that the little crystals of iodo-nitrate which 
 float in the nitrate bath deposit themselves on the film, and on this 
 account some photographers pour their silver solution from a bottle, into 
 which it has been filtered, after sensitising a considerable number of 
 plates. 
 
 At other times the bottom of the plate is riddled with holes. These 
 are caused by the concentration of the nitrate on account of the plate 
 having been kept too long between the sensitising aud the development. 
 
 Sometimes, when the nitrate bath has not been filtered for a long 
 time, a pellicle of reduced silver is formed, which attaches itself very 
 firmly to the film. Veins also occur, which are aptly represented by 
 fig. 66, page 63. (M. de la Blanchere.) 
 
 A similar class of stains sometimes occur, especially on positives, if 
 the bath contains an excess of alcohol, and they become visible on with- 
 drawing the plate from the sulphate of iron solution. 
 
 The stains shown in fig. 67, page 63, arise when too thick a collodion 
 is used. 
 
NOTES. 131 
 
 Pyrogallic acid often produces spots. If the developer prepared there- 
 with contains too little acetic acid, foggy pictures are the result. If it 
 contains too much, the development proceeds very slowly. But spots 
 occur less frequently in the latter case than the former. 
 
 Should too small a quantity of pyrogallic be poured on the plate, stains 
 develop themselves at the corner, and sometimes spread on to the centre ; 
 and nothing will remove them. 
 
 If the pyrogallic acid developer does not spread itself immediately 
 across the plate, it produces lines which are as irreparable as those stains 
 described in the previous instance. It is also very important to main- 
 tain a constant backward and forward motion during development, 
 otherwise a series of little black points of reduced silver will attach them- 
 selves to the plate. 
 
 Hyposulphite of soda, imperfectly washed away, sometimes agglome- 
 rates after the lapse of a certain time, and then produces star-like spots 
 of the form indicated fig 68, page 63. It is, therefore, of the highest 
 importance to remove the hyposulphite by repeated washing. 
 
 It remains to say a few words on fogging, the origin of which is two- 
 fold the first, diffused light, and the second, alkalinity of the bath. 
 
 The evil from the first cause arises generally from the inferiority of the 
 yellow glass, which does not completely arrest the passage of the actinic 
 rays ; sometimes from the lamp or candle giving off too much white 
 light, from a hole in the camera back, or in the camera itself, &c. 
 
 The second of these causes, alkalinity of the bath, is much more rare ; 
 it occurs generally in summer time when the weather is very warm. A 
 few drops of acetic acid in the nitrate bath will obviate this defect. 
 
 NOTE 10 (page 56). 
 CRYSTALLISABLE ACETIC ACID. 
 
 Where crystallisable acetic acid cannot be obtained, its nse may, to a 
 certain extent, be dispensed with, by the following plan. 
 
 One thousand five hundred grains of caustic potash are dissolved in 
 35 ounces of distilled water, to which is added 750 grains of powdered 
 litmus, and the blue liquid is decanted into another bottle. This bottle 
 should be kept carefully stoppered. Having obtained some good ordi- 
 nary acetic acid, called purified pyroligneous acid, and a tube divided into 
 cubic centimetres, two cubic centimetres of the blue solution of potash 
 are poured therein. Now add, drop by drop, some standard crystal" 
 Usable acid, becoming solid when exposed to a temperature of about 
 40 Fahr. ; and after each addition, shake the tube. A point will be 
 reached at which the blue solution allot once becomes red ; it is at this 
 moment that the operation is completed. 
 
 A note is made of the amount of acid which was necessary to change 
 the blue colour of the potass solution ; and suppose, for example, this to 
 have been a quarter of a cubic centimetre. Now begin afresh, by mixing 
 the solution of litmus with twice its volume of water, an d also the crys- 
 
132 PHOTOGRAPHIC PROCESSES. 
 
 tallisable acid with a similar proportion. This will allow the observa- 
 tion to be made more accurately as to the quantity of acid required to 
 redden a given quantity of solution of potash. Suppose that it is finally 
 ascertained that 10 cent, cubes of the blue solution require 1 to 1J cent, 
 cube of the crystallisable acid. Now perform a similar operation with 
 the pyroligneous acid ; this being much weaker, it will probably be found 
 that for 10 parts of the blue solution 3 J parts of this acid will be required. 
 The following equation is now made. If 1 J parts of pure acid correspond 
 to 3 J parts of ordinary acid, 10 of pure acid will correspond to x. 
 
 From this calculation is deduced the fact, that x is equal to 28 ; from 
 which it results, that every time 10 grains of crystallisable acid are 
 ordered in a formula, they may be replaced by 28 of ordinary acid : if 5, 
 14 only will be necessary ; if 30, 84 will be wanted, &c. &c. 
 
 The hydrometer cannot be used to determine the strength of acetic 
 acid, for its density bears no regular proportion to its saturating power, 
 or, in other words, to the relative quantities of acid and water. 
 
 The pure crystallisable acid solidifies between 50 to 60 Fahr. 
 Although the ordinary acid is only a mixture of pure acid and water, and 
 the first solidifies at, say 56 Fahr., and the second at 32", it does not 
 necessarily follow that the mixture shall solidify above 32. The pure 
 acid, mixed with three times its volume of water, should, at first sight, 
 solidify at about 40 Fahr., but, in reality, it does not congeal until it is 
 cooled to 36 below the freezing point of water; from which it follows, 
 very weak acid cannot be purified by successive and fractional freezing ; 
 and it is only when more concentrated, that this method of purification 
 can be adopted. 
 
INDEX. 
 
 Acetate of ammonia, use of, 86 
 
 Acetic acid crystallisable, 130 
 
 Aceto-nitrate bath for sensitising collodio-albumen glasses, 78 
 
 Achromatic lenses, 127 
 
 prisms, 127 
 
 Actinic rays, 48 
 Albumen, how prepared, 76 
 Albumen iodised, 75 
 Albumen process, 5 
 Albumenised paper, 101 
 Alcohol, properties of, 11 
 Amber varnish, 68 
 American clip, 104 
 
 Backgrounds, graduated, how produced, 108 
 Bath, nitrate of silver, for the wet collodion process, 30, 32, 123 
 collodio-albumen process, 73 
 
 Balance, hand, 21 
 
 Balance, table, 21 
 
 Brewster's stereoscope, 90 
 
 Bromide of cadmium, preparation of, 20 
 
 Bromine, 19 
 
 Cadmium, 19 
 
 Caloscopic lenses, 47 
 
 Calotype, the, 2 
 
 " Cartes de Visite," camera, 39 
 
 lens for taking, 47 
 
 Camera obscura, discovery of, 36 
 
 principle of the, 36 
 
 photographic, 37 
 
 bellows-body, or portable, 41 
 
 " Carte de Visite," 39 
 
 for travelling, 40 
 
 stands, 38 
 
 Cameras, stereoscopic, 92 
 
 positive collodion process, 86 
 
 printing process, 103 
 
134: INDEX. 
 
 Chloride of calcium, how employed, 1 05 
 
 gold, use of in toning, 1 13 
 
 sodium, use of in positive printing, 99 
 
 silver, how reduced, 75 
 
 Clouds, effect of, how produced, 110 
 Coating plates with collodion, 31 
 Collodio-albumen plates, development of, 80 
 
 albumen process, 73 
 
 Collodion, 6, 17 
 
 film spots on the, 131 
 
 for copying, 122 
 
 how decanted, 25 
 
 iodised, preparation of, 22 
 
 how preserved, 24 
 
 positives, how whitened, 88 
 
 preparation of, 122 
 
 process, negative, 30 
 
 positive, 84 
 
 dry, 71 
 
 Colours, separation of light into, 127 
 
 Combination lenses, for portraits and groups, 43 
 
 Crystal enamel, 119 
 
 Cyanide of potassium, use for the positive collodion process, 87 
 
 for removing stains, 123 
 
 Daguerreotype, 1 
 
 Dark frame for camera, 42 
 
 Dark room, 29 
 
 Developing solution for collodion negatives, 56 
 
 positives, 86 ^ 
 
 : collodio-alburnen plates, 80 
 
 tannin process, 83 
 
 Dextrine, 72 
 
 Diaphragm, meaning of, 37 
 
 Direct image, 3 
 
 Dry collodion processes, 71 
 
 Drying box for sensitised paper, 105 
 
 Ether, apparatus for distillation of, 15 
 properties of, 13 
 
 rectification of, 13 
 
 washed, 14 
 
 Exposure, to estimate time of, 52, 53 
 
 Fading of photographs, to avoid, 1 1 6 
 Fixing of positive paper proofs, 115 
 
 solution for negatives, 64 
 
 . positives, 87 
 
 tannin process, 84 
 
 Filtering, apparatus for, 11 
 Filters, how made, 11 
 Finger-stalls, 36, 
 
INDEX. 135 
 
 Focus, how obtained, 41 
 Focussing, meaning of, 37 
 Fogged image, how rendered, 85 
 Fogging, how caused, 131, 132 
 
 Gallic acid, use of with calotype process, 2 
 
 collodio-albumen process, 81 
 
 for rapid printing, 117 
 Gallo nitrate of silver, 3 
 Gelatine, Nelson's patent, 82 
 
 use of, 119 
 
 Glass clipping troughs, 34 
 
 plates, edges of, how ground, 25 
 
 how cleaned, 26 
 
 : dried, 67 
 
 preserved, 43 
 
 room, 48 
 
 colour of, 50 
 
 Gold, chloride of, use in toning, 113 
 Gun cotton, discovery of, 18 
 
 - preparation of, 16 
 
 Head rests, 51 
 Hyposulphite of soda, 64 
 
 Iconometer, 54 
 
 Incident ray, 124 
 
 Indirect image, 3 
 
 Intensifying collodion negatives, 66 
 
 Iodide of cadmium, preparation of, 19 
 
 ethylamine, 122 
 
 potassium, use of in rapid printing, 117 
 
 Iodine, 19 
 
 Iodised albumen, 75 
 
 Kaolin, how employed, 78 104 
 
 Laboratory, photographic, 29 
 Lenses, achromatic, 127 
 
 caloscopic, 47 
 
 concave, 126 
 
 convex, 126 
 
 double or compound, 45 
 
 -focus of, 126 
 
 orthoscopic, 47 
 
 portrait, 45 
 
 photographic, 43 ' 
 
 various forms of, 127 
 
 for views, how used, 44 
 Litmus paper, 1 8 
 
 Measures, glass, graduated, 21 
 
136 INDEX. 
 
 Negative image, 3, 4 
 
 .Negative image, 3, 4 
 Nelson's patent gelatine, 82 
 Nitrate of silver bath, 30, 32, 123 
 
 preparation of, for negative process, 123 
 
 stains, to remove, 123 
 
 use for collodio-albumen process, 73 
 
 use of in negative collodion process, 30 
 
 Dositive collodion process. 86 
 
 I llGgttilil. VG ^\Jll<JUllUll plU^^OO, U\J 
 
 positive collodion process, 86 
 
 Orthoscopic lenses, 47 
 
 Paper, albumenised, 101 
 
 photographic, 99 
 
 salted, 99 
 
 Photographs, mounting of, 116 118 
 Photographic optics, 124 
 Pictures, formation of, by lenses, 128 
 Plate box, 43 
 Plate-holder, 27, 58 
 Pneumatic plate-holder, 58 
 Portrait lenses, 43 
 Portraits, rules for taking, 52 
 Positive collodion, preparation of, 84 
 - process, 84 
 
 image, 3 
 
 printing, rules for, 107 
 
 prints, mounting of, 116 118 
 
 proofs, fading of, to avoid, 116 
 
 fixing of, 115 
 
 toning of, 112' 
 
 varnish for, 118 
 
 Positives, collodio-albumen, 79 
 
 transparent glass, 79 
 
 Pressure frames for printing, 108 
 Printing frame, 106 
 
 process, 98 
 
 the rapid, 116 
 
 Prisms, achromatic, 127 
 
 refraction of, 125 
 
 Protosulphate of iron, use of, 86 
 Pyrogallic acid, preparation of, 129 
 
 use of, 55 
 
 Pyroxyline, preparation of, 6, 17, 122 
 
 Reducing agents, 55 
 Reflection of light, 124 
 Refraction of light, 1 24 
 
 through prisms, 125 
 
 Rolling press, for glazing proofs, 118 
 Russel's tannin process, 82 
 
 Salted paper, 99 
 
INDEX. 137 
 
 Sel d'or, how used, 116 
 
 Sensitising collodionised plates, rules for, 36 
 
 solution, for paper, 103 
 
 for positive collodion, 86 
 
 Separation of collodion film, to avoid, 65 
 
 Soehnee varnish, 68 
 
 Spots on the collodion film, 131 
 
 collodion negatives, 63 
 
 Stains on collodion film, how caused, 131 
 negatives, 63 
 
 - of nitrate of silver, to remove, 123 
 
 Stereoscope, phenomena of the, 89 
 
 Sir David Brewster's refracting, 90 
 
 Wheatstone's reflecting, 90 
 
 Stereoscopic angle, explanation of, 96 
 
 angles, table of, 97 
 
 cameras, 92 
 
 pictures, how mounted, 118 
 
 obtained, 93 
 
 Stop, meaning of, 37 
 Support for glass plates, 26 
 
 Tannin, from what obtained, 82 
 
 process, 82 
 
 Taupenot's process, 71 
 Toning process, the, 113 
 
 Varnish, amber, 68 
 
 for positive proofs, 118 
 
 soehnee, 68 
 
 Varnishing negatives, 67 69 
 
 ~ positive collodion pictures, 88 
 View lenses, 43 
 
 meter, 54 
 
 Views, rules for taking, 53 
 Vignette glasses, 108 
 
 Washing bottle, 57 
 
 Washing collodion negatives, 65 
 
 Wheatstone's stereoscope, 90 
 
 Yellow light, action of, 48 
 
 James S. Virtue, Printer, City Road, London, 
 
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