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X~~~~Taº · ·,≤） 3.* , ，; **: < .??！！！ ſſſſſſſſſfīlīīīīīīīīīīīīīīīīīīīīīīīīīīīīīīīīīī~ CN（CZĘST ，，A HÌÌÎÎÏÏĪĪĪĪĪĪĪĪĪĪĪĪĪĪĪĪĪĪĪĪĪĪĪĪĪĪĪĪĪĪĪĪĪĪĪĪĪĪĪĪĪİ → • ſº imminſ se tº gº gº tº a c e º ºr sº gº º ºr º e º ºr e º ºr e º ºr e º ºs e º ºp e Tulluminimum ºnlintrºlliſt Eºse ease a see sº º ºxea ea sºle cºee e. e. Ellrºllinºlºuriſtin, ŒŒŒ Œ Œ ）（.*; Lº f ºRMAMAtºlºmºſºſtºlºpºlºkºlºnſºrtiºnnatinºttiſtiniºntinºiſſiſſiſſilſ IIIllſlºt. º º- •F &=3 Cº- Cº- º- C - G - &E gº [−. vºs OTſū. o Hºc THE GIFT OF & <> & ) \\w Wyv- xxxxxxxxxxxxxxxxx8= ſaeuaediff | The DIME Series of * Photographic - W tº Handbooks No. 5 * . Isochromatic Photography ſº * - - By . 10c. R. James Wallace The Photo-Beacon Exposure Tables - are Guaranteed Correct. Price, 25c. 30,000 Copies Sold. ſº “Worth their weight in gold.” GEO. T. TODD, U. S. Weather Bureau, " Dodge City, Kan. “They haye been worth to me $200.00.” G. F. GREEN, Waynoka, O. T. The Photo-Beacon Co. , 409 Security Building. . Chicago . Eastern Office: 621 Broadway, New York In our Non-Halation Orthochromatic Plate we believe we have reached the highest point of excellence yet attained in dry plate making. It is our regular Non-Halation plate with the exception that it is coated with our Landscape Ortho emulsion instead of 26x. The results show that not only are the most difficult contrasts in landscapes and seascapes photographed with absolute fidelity to nature, but the color values are there as well. If our light filter—the Chromatic Curve Corrector is also used, the color values will not only show, but the different colors will be photo- graphed in the exact relation as seen by the eye. we have a circular giving a description of the action of color in photography. Your dealer has them, or we will mail direct on request. M. A. Seed Dry Plate Co. St. Louis, Mo. New York, N.Y. Instantaneous Exposures & The Cleanest, Most Uniform and Reliable Plate on the Market. CONCEDED BY ALL TO BE THE RIGHT SPEED HAMMER EXTRA FAST . PLATE (“Hammer's Little Book,” a short talk on negative- making, mailed free on application.) | Hammer Dry Plate Co., ST. LOUIS, MO. PY RO IS THE BEST M . DEVELOPER LOOK OUT FOR THIS SEAL IN RED ON EVERY PACKAGE REGISTERED, THE BEST PYRO. IS SCHERING'S FOR SALE BY ALL DEALERS The only other Book about Orthochromatic Photography No. 6 THE PHOTO-MINIATURE, (more than 10,000 sold) You should have them both Trice 2.5 cent r From your dealer if he has it, or TENNANT AND WARD." 287 FOURTH AVE., NEW YORK ISOCHROMATIC PHOTOGRAPHY BY R. JAMES WALLACE *~ CHICAGO : THE PHOTO-BRACON COMPANY. - . . I902. Eastern Office: 611 to 621, Broadway, New York. : CopyRIGHT, 1902, BY F. DUNDAS TODD, ISOCHROMATIC PHOTOGRAPHY. *-*. CHAPTER I. LIGHT AND COLOR. In entering upon this series of articles explanatory of the principles and prac- tice of “orthochromatic ’’ or “ isochro- matic ’’ photography, it is my intention to start from the very beginning of the subject, assuming that the reader knows ... absolutely nothing beyond the ordinary !, practice of negativemaking — exposing * and developing — and should this . S. method appear to some to be unneces- • sary, I beg their indulgence for the sake § of the many others who do not know, feeling that, in justice to the subject, this is the only course to pursue. My aim is to make this series a fairly com- , , plete record of experiments that will serve not only as a guide to the beginner but for reference to those who are more advanced * 32320 : 4 ISOCHROMATIC PHOTOGRAPHY. Starting thus at the beginning of the subject, I shall first consider the phe- nomena of light and color, but only in so far as they concern the photographer, passing over everything which deals with the wave and undulatory theories as being beyond the scope of this series, and which can readily be found by the student in any book on physics and will therefore plunge at once into the analy- sis of light known as the spectrum. - When a beam of white light is passed through a prism it is spread out into a colored band containing six distinct colors, as follows: red, orange, yellow, green, blue and violet. Some writers claim seven colors and add “indigo" between the blue and violet, but as this color is simply a deeper and darker form of blue, showing but little difference from the color preceding it, and as the object of this article is to simplify as much as possible, we shall consider the spectrum as composed of the six colors already mentioned. - - Now these six colors are not definitely separated or divided, but merge imper- ceptibly the one into the other, so that it is practically impossible to state where the one leaves off or the other begins. ISOCHROMATIC PHOTOGRAPHY. 5 This may be observed by passing a beam of daylight from any small opening through any kind of glass prism. If the light be taken from a very nar- row slit the spectrum is found to be very sharp and clear, and furthermore, it is seen to be characterized by the pres- ence of a number of dark lines or bands which are known as the Fraunhofer lines (from the name of their observer) which cross the spectrum at right angles to its length (Fig. I), and which serve as markers or milestones to instantly point out position in any spectrum under observation. It is sufficient to state that these lines are always present in the spectra of sunlight; always exactly in the same position and distance from each other. What they indicate it is not necessary to explain here. • The instrument for visually observing the spectrum is known as a spectroscope. Fig. 2 is from a photograph of one of the instruments in my laboratory with which most of my visual spectroscopic work is done. It consists of three tubes entering into a central chamber (from which the cover has been removed to show the prism). A is the collimeter or slit tube through which the light ^ 6 ISOCHROMATIC PHOTOGRAPHY. A Ot B Red. C Red-orange. D range. Orange-yellow. "Yellow, Green-yellow aſı Yellow-green. E } Green and Blue-green. Cyan-blue. F \ Blue and ſ Blue-violet. t } Violet, |- FIG. I. ISOCHROMATIC PHOTOGRAPHY. 7 8 ISOCHROMATIC PHOTOGRAPHY. ! passes and is focused on the prism P by a lens which is held at the inner end of the tube. B is the scale tube with its illuminating burner F and bears S, which is a very small millimeter scale divided into tenths, which is also fo- cused upon the prism (rear surface), by a lens L in its own tube, while C is the telescope with its focusing screw D for the observation of the spectrum as it emerges from the rear surface of the prism, together with the reflected scale. There is further an additional small prism H, fixed immediately in front of, and in contact with, the outer surface of the slit plate K, the use of which will be described later. N and M are screws . for moving the telescope in the observa- tion of special portions of the spectrum." Although, as has already been stated, the Fraunhofer lines serve to record any particular place or position on the spectrum, yet this only serves when the spectrum considered is that of daylight, for in the spectrum of artificial light the lines are absent and the appearance presented to the eye is that of one un- broken colored band, and as it would, under those circumstances, be impossible to specify or particularize any one posi- ISOCHROMATIC PHOTOGRAPHY. 9 - tion, the reflected scale is used instead, and before beginning work this scale is carefully adjusted by the screws X, X2, so, that the line marked 5.o is exactly coincident with the D or Sodium line, that all readings may be directly com- parable the one with the other. Although this instrument is one of the very best for visual work, yet the com- bination Öf lenses in the observing tele- scope is altogether unsuited for work of a photographic nature, to say nothing of the cumbersomeness of the apparatus, so I use for this latter purpose, a direct- vision spectroscope which is readily adapted to the camera and is shown in position in Fig. 3. A is the spectroscope and is held firmly by the solid brass base B, and entering directly in the center of the lens which projects the spectrum upon the ground glass of the camera C. The direct vision spectroscope, Fig. 3, differs from that of angular vision, Fig. 2, by its containing a combination of five prisms of flint and crown glass , alternately. By these the spectrum is projected in a straight path parallel to the length of the tube, and once a sharp focus is obtained, one may reflect a strong beam of sunlight from a heliostat IO i - - - - - - - º -- - • - - - - - - ISOCEHROMATIC PHOTOGRAPHY. II (which is focused upon the slit by the lenses X and X2) and make a prelimi- nary exposure upon a sensitive plate. If the instruments be now clamped down in the same position, incandescent gas or any other source of light may be used for further experiments, the first expos- ure giving the record of the Fraunhofer lines to serve as “finders ” for all fol- lowing. - In Fig. 4 I show the arrangement used by me for incandescent gas. The two condensing lenses X and X2 with their carrying board are pivoted and swing aside out of the way, while their place is taken by the projecting lantern which has the lenses arranged for a small parallel beam of light of great intensity that falls directly upon the slit. It is with this latter instrument arranged as in Fig. 3, that all the spectra used in the illustration of this series were made; no extra care being taken to render the lines microscopically sharp but only sufficient to give the principals. One other device which has been used is that of a brass-cap which fits cleanly but loosely over the slit of the spectro- scope and which is pierced with a circu- lar opening which is again divided in ; ; ”, ... y - / ISOCHROMATIC PHOTOGRAPHY. r −.- -- - -） ſ |-- |- |- | ſ |- |- |- - |- |- |- |- • • • • • · - • • • • • • - - - - - - - - - - · - - - - - - |- |-|- ISOCHROMATIC PHOTOGRAPHY. 13 half by a tongue of metal on the inside. In use this cap is placed upon the front of the spectroscope, and the projecting tongue of metal being vertical, it cuts off or covers up just one-half of the slit — say the upper half. The plate is un- covered in the camera, the light turned on for the proper length of time and the spectrum impresses itself. The light is then shut off and the cap turned around one-half of a revolution, so that the upper half of the slit is now open while the lower, half is covered. The screen or tank of dye is placed upon the plat- form P in front of the spectroscope, and the light again allowed to pass, the new spectrum impressing itself in turn im- mediately below the first one, with all the lines exactly coinciding and show- ing at a glance the sensitiveness of the plate to white light and the range of sensitiveness when screened with the particular dye that was used (Fig. 5). I have had photographs of spectra shown me by several embryo specialists which had been made by artificial light (with- out any lines or scale) and save only for the statement of the exhibitor — which might or might not be true — it was im- possible to fix what portion it was that I4 ISOCHROMATIC PHOTOGRAPHY. had been photographed. It might have been the green, or the yellow, but then again it might have been the blue — there was no means of proving the state- FIG. 5. ment. With this method of two spectra on each plate there is no possibility of mistake, for in the first place the position is fixed by the presence of the lines; in the second place it is oriented against the unscreened spectrum of the plate. ISOCHROMATIC PHOTOGRAPHY. I5 CHAPTER II. } CoLoR CONSTANTs. The next thing which must be con- sidered is what are known as the “color constants,” and it is necessary, if the student desires to become proficient in isochromatic work, that he thoroughly understand this subject. It presents no difficulty and it opens out to him the entire field of colorwork and its bibli- ography. y - Although we can isolate a small col- ored slip in the spectrum and fix its positions by means of the neighboring lines, yet that is not sufficient — we must be able to refer to it in some more definite manner, and understand some- thing more about it. Electricity is divided and governed by three “constants * called the volt, the ampere and the ohm, and in the same way the science of light and color is governed by its three constants called Hue, Purity and Luminosity. The hue I6 ISOCHROMATIC PHOTOGRAPHY. of a color is that which first impresses us, namely: It is red, yellow, green, blue, etc. The second constant, that of purity, means that it is a hue which is unmixed with white. A pure color does not necessarily mean a bright color, for the spectrum contains colors which are pure and yet they are of unequal de- grees of brightness — the yellow for ex- ample is much brighter than the red or blue, and this brings us to the last con- stant, that of luminosity. This is what may be termed the “brightness” of color and means the total amount of light which it reflects to the eye, and is thus perfectly independent of the hue and the purity — for example, a small quantity of black may be mixed with some pure yellow and it may be com- pared against a blue. The yellow, although degraded with the presence of the black, would still be brighter than the blue, therefore, to speak correctly and scientifically, the hue would still be yellow, the purity would be lower than that of the blue, while the luminosity would be higher or greater. It is very necessary that the student thoroughly comprehend this before going further—for these terms will be ISOCHROMATIC PHOTOGRAPHY. 17 \ - in constant use throughout these articles, and if this point is not definitely under- stood, then neither will what follows. He must, therefore, study carefully this “dry” explanation and in the end he will realize that there can be nothing of more absorbing interest than this sub- ject of “light and color.” - I have now come to the point where I find it necessary to use the graphic method of explanation, one that will appeal to the eye better than will a mass of printed characters, a method which in the form of an illustration shall por- tray at once the special characteristics of what is being discussed, incorporating in itself its own explanation, and doing it better than any number of pages of reading matter. - Should I be desirous of showing to my readers by the aid of an illustration the effect of the solar spectrum upon normal vision, the course, that would naturally suggest itself would be to give a picture of the spectrum, but as this is particularly difficult to prepare, there is fortunately another method known as the spectrum curve, which can be em- ployed and which I shall now endeavor to explain. g 18 ISOCHROMATIC PHOTOGRAPHY. The luminosity or brightness of a beam of white light is, for the sake of convenience, always taken to represent IOO units. Now if this IOO unit beam be analyzed by a prism, it will, of course, be broken up into its six primary colors, and each one of these six must, there- fore, represent some definite number of the primary IOO units, and Rood has calculated just what is that interrela- tionship between them in the following table: - Dark red. . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Pure red. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. O5 Red . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4. 57 Orange red... . . . . . . . . . . . . . . . . . . . . . . . . . II. 50 Orange and orange yellow. . . . . . . . . . . . 28. Io Orange yellow. . . . . . . . . . . . . . . . . . . . . . . 32.76 Greenish yellow, yellow-green and 8TCtrl . . . . . . . . . . . . . . . . . . . . . . . . . . . I2.59 Blue-green and cyan blue. . . . . . . . . . . . . 4. 57 Blue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. OS Ultramarine ..... . . . . . . . . . . . . . . . . . . . . .37 Blue-violet . . . . . . . . . . . . . . . . . . . . . . . . . . . I4 Violet ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . O5 Recollect, therefore, that although the colors are practically pure, the lum- inosities (brightness) are vastly differ- ent, as the above table, and the most superficial observation of the spectrum shows; so, if we take a piece of paper ISOCHROMATIC PHOTOGRAPHY. 19 ruled off into squares of equal size and ten squares high, each square will stand for ten units of luminosity and the en- A FIG. 6. tire height for Ioo (white light). Fur- ther, if the number of squares hori- zontally be divided off by appropriate marks (either pointed off on the base line or continued up through the en- tire height) and marked to represent the lettered Fraunhofer lines, then it be- comes an easy matter to show any spectrum which one may be desirous of illustrating. For example: By the curve in Fig. 6, the visual appearance and correct luminosity of the solar spec- trum is shown. First the horizontal lines being marked off from O to IOO on the side, and the Fraunhofer lines indicated, we see by reference to the table that the yellow about the region of the D line has the highest luminosity, while the blue about G is very low, etc.; there- 2O ISOCHROMATIC PHOTOGRAPHY. fore, yellow, as possessing the highest luminosity, is placed at IOO. This is pointed off and so on with the remain- ing colors, and then these points are FIG, 7. all connected by a line as shown, thus giving at a glance an illustration of the extent and luminosity of the spectrum. Again we desire to record the effect of the spectrum of white light after pass- ing through a solution of picric acid — which absorbs the violet and blue of the spectrum. The action is graphically shown in Fig. 7, where, as may be seen, the curve dies down at about the region of the “F” line, and what in Fig. 6 was blue or violet is now represented by blackness or absence of light. Reference now must be made to the change in the spectrum after passing the beam of white light through a colored screen or colored solution of some dye stuff. The usual observation made by any one upon looking through a sheet of red glass is to the effect that everything ISOCHROMATIC PHOTOGRAPHY. 21 has been “turned to red,” but from what has already been said, the student is now in a position to know that this is not so. The white light falling upon the object has not been changed, but the red glass has simply stopped all other light than the red, generally speak- ing, and all the remaining five colors which go to compose the white light are absorbed by the glass, and stopped or extinguished, just as distinctly as does an extinguisher on a candle flame. 22 ISOCHROMATIC PHOTOGRAPHY. CHAPTER III. HUE AND PURITY OF COLOR. It is proper that we now enter a little more deeply into the problem of hue. and purity of color. As it is impossible with normal vision to distinguish the component colors in white light, so is it impossible for the eye to distinguish with even a rough degree of accuracy the different admix- tures which go to make, up a “color.” We look through the red glass and we 1D / Tis b=- D ſº b G ºf lº FIG. 8. N- say that it passes “red ” and that is all we can say; everything to which we ISOCHROMATIC PHOTOGRAPHY. 23 direct our vision is of that color and therefore we feel confident that that is the Only one the glass allows to pass; but, place that same glass in front of the slit of the spectroscope and we can see that in all probability not only is the red allowed to pass freely, but also the Orange and yellow, together with a little of the darker blue. In the same way we may take a yellow glass, and upon analyzing the light transmitted through it by the spectroscope we find that, be- sides the yellow, it also transmits the red, the Orange and the green. And a f : Miſſºul ºr ſºlº } Wºł } [MT IN ºut $ 1 º'D Yūlūtº - ſºl Ut. Gºl A$$ Glå$º FIG. 9. so on with any number of glasses of dif- ferent colors — all will be found to transmit, not a single color, but a mix- ture. - Again, we may take a yellow glass and a blue glass, and superposing the one 24 ISOCHROMATIC PHOTOGRAPHY. upon the other, we find upon looking through them that the resulting hue is green. Why is this? Let the diagram in Fig. 8 assist in the explanation. The D E b f G H. K. FIG. Io. upper curve exhibits the analysis of the light transmitted by the yellow glass, which, as shown, passes the red, orange, yellow and green, while the lower curve illustrates the light transmitted by the blue glass, which also allows the green to pass, together with the blue (and a small portion of the red). When they are superposed the result is green, sim- ply because both glasses allow that color to pass through freely, while they stop or extinguish all other colors, as Fig. 9 may possibly assist in making plainer. In the colors of nature we are not dealing with spectral or pure hues be- cause from the infinite variety of angles which objects present to the eye there is always present more or less white, and it is this, in a great measure, which is ISOCHROMATIC PHOTOGRAPHY. 25 the principal cause of unlikeness (other- wise than shape) in a photographic rep- resentation. It must not be supposed that the colors of the spectrum have the power equally to impress themselves upon the photo- graphic sensitive plate with their rela- tive luminosity; in fact, it was early discovered that their power in this re- spect was very limited — the red, orange, yellow and yellow-green abso- lutely refusing to show action, while the blue-green, blue and violet were strongly active. In short, the solar spectrum, as shown by its impression on the sensi- tive plate, is graphically depicted by curve in Fig. IO, and again by a spec- trum print in Fig. II, which is repro- FIG. II. duced from an impression on an undyed and unscreened plate, one that may be taken as representative of its class, namely, Seed 26 X. In this it will be noticed that even the blue-green with a 26 ISOCHROMATIC PHOTOGRAPHY. higher luminosity than the blue, photo- graphs much darker. It should also be noted that all plates are sensitive in a slightly inferior degree to the invisible ultra violet rays extending to the right beyond the K line, and which are not shown in the print because sufficiently prolonged development to show this re- gion would choke up the lines in the visi- ble spectrum between F and H. Now, let us compare the above “curve of sensitiveness,” as it is called, with the “curve of visibility,” as shown in Fig. 6. A glance is sufficient to show the great difference; for, whereas, in the visual spectrum the highest lumi- nosity is shown to lie in the yellow, the greatest sensitiveness is here shown to be in the blue — to say nothing of the fact that the spectrum of plate sensitive- ness absolutely ignores and takes no cog- nizance whatever of fully one-half of the colors which go to make up the spectrum. Scientifically, this plate is (generally speaking) totally insensitive to certain hues, and entirely wrong in regard to luminosity. And it is to the researches of Dr. Eder that we are in- debted for the knowledge that a plate capable of representing the colors of the ISOCHROMATIC PHOTOGRAPHY. 27 spectrum with their relative luminosity should show deposit as follows: The orange at C and the blue at F should be rendered by equally dense deposits; the yellow at D by a deposit six times as dense as this, the green at E by one three times as dense, and the end of the visible violet by one ten times less dense. To render the matter still more plain, were we to expose this plate upon a subject composed of a square each of pure yellow, red and blue, where the yellow is of the highest luminosity and the blue of the lowest, with the red mid- way — with normal exposure — the plate would give us the exactly opposite effect, as follows: Blue, brightest, and the yellow and red equally black, and it is to remedy this that the so-called isochromatic plate was introduced. To the beginner the use of such a plate is associated in his mind solely as a means of securing clouds with the landscape at one exposure, and the most erroneous ideas are disseminated broad- cast (unconsciously perhaps) by the many large display frames sent out by the plate manufacturers, and hung in conspicuous positions by the dealer. Isochromatism (or orthochromatism) 28 ISOCHROMATIC PHOTOGRAPHY. is a name derived from two Greek words which signify correct color, so that an orthochromatic plate means a “correct color * plate. Although custom has ren- dered its use general, yet the name has not been wisely chosen, for the plate does not reproduce objects in their cor- rect color (nor is it intended to), but is supposed to represent colors in their relative luminosity. There is no plate yet manufactured, either in Europe or America, which is more than an approx- imation to the desired result. ISOCHROMATIC PHOTOGRAPHY. 29 CHAPTER IV. ISOCHROMATISM. It was early discovered (Vogel, 1873) that by introducing a small quantity of dye into the emulsion (either, in the process of manufacture or by later bath- ing), the plate so stained exercised a selective action to certain rays of the spectrum to which it had been pre- viously insensitive. Thus, a plate which had incorporated in its substance a small quantity of eosin was found to possess a sensitiveness to the yellow-green of the spectrum in addition to the sensi- tiveness which, as an emulsion, it al- ready possessed to the blue and violet. Again, the addition of a minute quan- tity of quinolin blue confers a special sensitiveness to the yellow orange, and part of the red, besides the original sen- sitiveness to blue and violet. * Many are the dyes that have been tested and used for this purpose, but sufficient for the purpose of explanation are the two which have been mentioned 30 ISOCHROMATIC PHOTOGRAPHY. | || D Eb G A—Brilliant yellow. Cramer slow iso. B–Brilliant yellow. Cramer medium iso. C–Cramer medium iso. Anilin blue and Fluorescein. D—Ammonium picrate. Cramer medium iso. FIG. I.2. ISOCHROMATIC PHOTOGRAPHY. 31 A—Acridin yellow. Seed 26 X. B—Seed 26 X. Brilliant yellow. C—Seed L. Ortho. Methylene blue and chrysoidin. D—Cramer crown. Solar. FIG. I.3. 32 ISOCHROMATIC PHOTOGRAPHY. above, for it is not necessary to enter into the details of manufacture, such plates being now a regular article of sale, and found on the shelves of almost every supply house. The isochromatiz- ing of plates by the individual is a mat- ter not to be considered, save only by the experimentalist who is desirous of ob- taining a special action on a definite portion of the spectrum. The dye stuffs which are used for this purpose are very unstable in their com- position, the action of a beam of light being sufficient to bleach them some- what, so that when the light which passes the lens falls upon the extremely minute amount present in the plate film, the molecular arrangement of the dye is disturbed, and that disturbance is communicated to the plate when under the action of a developer. There is a law which governs this ac- tion, which runs as follows: A plate is acted upon by the color which it ab- sorbs; for instance, eosin (a red dye) absorbs green, therefore the plate is ren- dered sensitive to green because that is the color which the dyed film absorbs. Quinolin blue (a blue-violet dye) ab- sorbs yellow, orange and part of the ISOCHROMATIC PHOTOGRAPHY. 33 P # G H | | A—Methyl green and picric acid. Seed 26 X. B–Gentian violet. Seed 26 X. C—Cyanin. Seed 26 X. D–Fluorescein (note action of violet). Seed 26 X. FIG. I.4. 34 ISOCHROMATIC PHOTOGRAPHY. red and green, therefore the film is sen- sitive to these hues. In other words, the green which would pass on through the film is held back (absorbed) by the dye, and under the influence of that ab- sorption is compelled to perform certain work in the film, the nature of which is at present but little understood. - Now, so far, the problem seems to be a very simple one indeed, but there are many difficulties yet to be overcome be- fore color can be rendered with even the roughest approximation to correct lumi- nosity, for, although the plate has un- doubtedly been rendered sensitive to, say, green, yet its sensitiveness to the blue, violet, and ultra-violet are still unim- paired, and these hues must be reduced, dimmed down or cut off, in order that the slower sensitiveness of the other col- ors may get an opportunity to catch up, , as it were, with those of greater rapidity. This is the sole purpose of the screen or ray filter, and the correct understanding of which is the key to intelligent use. In the lower half of the first double spectrum of Fig. I2 is shown the sensi- tiveness of a plate stained with one of the Fluorescein derivatives, namely, Cramer Slow ISO. It will be seen that, t ISOCHROMATIC PHOTOGRAPHY. 35 P º f ; # A—Chrysoidin. Solar spectrum Seed 26 X. B—Iodgrun and picric acid. Seed 26 X. C–Picric acid (saturated). Seed 26 X. D—Auramin. Seed 26 X. FIG. I5. 36 ISOCHROMATIC PHOTOGRAPHY. although there is a sensitiveness to the orange red of the spectrum, yet that sensitiveness is very low compared with that to the blue and violet. This print is made very light purposely in order that this point may be apparent, for were it printed up to average strength then that orange sensitiveness would not show at all. Now you can readily see that if we desire to show color in its correct luminosity we must first cut off entirely the ultra-violet rays (which are invisible to the eye) and dim down the violet and blue so that they may be held back long enough to give the green, yel- low and orange a chance to impress themselves upon the plate with equal strength, and this is accomplished by the use of a yellow screen, for, as we have previously seen, yellow cuts off or dims down these colors, according to the strength of the color. Thus we learn why an isochromatic plate and yellow screen render it possi- ble to secure whatever cloud effect may be in the view photographed — simply that the blue of the sky is dimmed or slowed, while the white of the cloud (of higher luminosity) passes through un- absorbed. ISOCHROMATIC PHOTOGRAPHY. 37 A—Carotin. Cramer Med. iso. B–Eosin bluish and picric acid. “Erythro” solar. C–Nile blue and Auramin. Cramer inst. iso. D—Cramer inst. iso. Light green F. S. FIG. I6. 38 ISOCHROMATIC PHOTOGRAPHY. It is most erroneously supposed by the general mass of photographers that any ray filter or yellow screen is suitable for use with any iso. or ortho. plate, but this is not so. Take the illustration shown in the last double spectrum of Fig. I2, which is representative of this class of plate, namely, Cramer instantaneous isochromatic, and it will be seen that although the use of a yellow screen is beneficial, yet it is only partly so. True, we can, by its means, cut off the blue-violet and ultra-violet, but the work is only half done; the plate is still sensitive to the yellow-green and blue to an abnormal degree compared with the blue-green, yellow and orange, and sufficient action will take place upon the plate to give a fully exposed negative by the action of those rays alone, long before that blue-green (of which the greater part of a landscape is composed) begins to impress itself. The remedy is very obvious, for if we introduce a colored filter to dim down the too strong action of the blue-violet then we must introduce another to dim down the yel- low green. In other words, a ray filter must be adjusted to the plate with which fit is intended to be used, so that a filter ISOCHROMATIC PHOTOGRAPHY. 30 C -ei --> G | A B C D H | | D Eb F G H A—Ethyl violet. Seed 26 X (cyanin stained). B—Fast scarlet and picric acid. “Erythro.” C–Eosin and naphthol yellow. Lumiere panchro- matic. D—Aurantia. Seed 26 X. FIG. 17. 4O ISOCHROMATIC PHOTOGRAPHY. adjusted for the plate now under con- sideration should not be yellow only, but a mixture of yellow and crimson in proper proportion, as it is the crimson which acts upon the yellow-green. Some isochromatic plates have their strongest action in the yellow, and for such a plate a perfectly adjusted filter would be a mixture of yellow and blue, the latter dimming down the yellow. Of course such a screening down of the colors means a lengthened exposure, but this is amply made up for in supe- rior effects, the resultant tones being more in harmony with one another. It may be interesting to note that the firm of Cadett & Neall, of England, now manufacture a light filter and “safe light" specially adjusted to their plate. In fact, they manufacture two light fil- ters, which they name, respectively, the “Gilvus ” and the “Absolutus,” and give specific instructions for their use, plainly saying that the former (the Gil- vus) is merely a makeshift, as it were, to be used when the object is speed, but also stating that for correct work there can be no change from the “Absolutus.” Carbutt, in this country, has a specially designed “safe light” for his polychro- ISOCHROMATIC PHOTOGRAPHY. 4I matic plate, also adjusted ray filters for use with it. In spectrum work there is still another plan for obtaining stationary lines or G H | A—Chinolin red and picric acid. Carbutt Ortho. B—Seed L. ortho. Naphthol green. - C—Seed L. ortho. Naphthol green and erythrosin. FIG. I.8. markers than by the use of the solar spectrum. Each metal has its own par- ticular spectrum, which is distinguish- able from another by the number and position of its lines. So when a metal is 42 ISOCHROMATIC PHOTOGRAPHY. burned before the slit of the spectro- scope, those lines which compose its spectrum stand out as luminous bands. It is sufficient to state that these lumi- nous lines are just as immovable as are the dark Fraunhofer lines in the sun spectra — in fact, the two are identical, only they are observed under different conditions. The power to obtain bright lines at any time is very useful, for, as in the case of Fig. 18, they are shown by the simple method of burning a few inches of magnesium ribbon in front of the slit. In this case the magnesium had been previously moistened with dilute hydrochloric acid, and dipped in lithium chloride, thus giving in addition the splendid lithium line between B and C. The number of dye stuffs which can be used for special purposes are very many, and from hundreds I select a few in Figs. I3 to 18, which will serve to show their values and screen- ing action when used as filters for spe- cial purposes. In all cases, as may be seen, the unscreened spectrum of plate sensitiveness is indicated by the solar sign — a circle with a dot in the center. ISOCHROMATIC PHOTOGRAPHY. 43 CHAPTER V. A SPECTROSCOPICALLY CORRECT COLOR SENSITOMETER. In this chapter I shall discuss the par- ticular advantages of a specially de- signed color sensitometer (or plate tester), which has been perfected by the writer for the benefit of those workers in photography who may not be inclined to invest a considerable amount of money in providing themselves not only with the necessary instruments, but with the knowledge to use the same. One writer tersely says, “ Mortgage your home and buy a spectroscope,” but to some this method presents certain dis- advantages which may, in their minds, be not quite equaled by the possession of the instrument. Abney (an eminent authority on all photographic research work) first intro- duced the idea of such a sensitometer, but he did not carry the detail of the idea to the point of perfection which 44 ISOCHROMATIC PHOTOGRAPHY. would make it replace the 'spectroscope to all but the physicist, and after much experimental work the writer has suc- ceeded in being able to place in the hands of the photographer an improved form of sensitometer which, if used with the average amount of intelligence, will perform the necessary work and . give clear and definite results. It consists essentially of a series of eight colored transparent squares, to- gether with a “white,” which are ad- justed to transmit the following: No Hue Fraunhofer lines. Scale. I Dark red. . . . . . . Passes color only from A to B . . . . . . . . . I.5 to 2.9 2 | Red . . . . . . . . . . . & C { { ** ** A ‘‘ C . . . . . . . . . I.5 “ 3.5 3 | Light red . . . . . . © (ſ ( & “ “ A “D minus...| 1.5 “ 4.8 4 | Orange . . . . . . . . £ 6. & C “ “ A “D plus ....| 1.5 “ 5.3 5 || Yellow-green .. ſ & ( & “ “ D # E to b . . . . . . 5.3 “ 7.5 6 | Blue-green . . . . . £ 6 { { “ “ E to F . . . . . . . . . 7.o “ 9.o 7 | Blue. . . . . . . . . e § { £ & ‘‘ ‘‘ F ‘‘ G . . . . . . . . 9. O “ I2.7 8 | White. . . . . . . . . . All colors in white light. . . . . . . . . . . . . . . . . . . . . - - - - - 9 A rectangular slip of blue-violet which passes color from F to H, plus, 9.o. to 16. I, and which also passes a band of red from A to almost the C line, I. 5 t - a - O 3.3. º à 46 ISOCHROMATIC PHOTOGRAPHY. In addition there is a series of twenty smaller squares of neutral gray which divide a beam of light from its highest luminosity (IOO) to opacity (O) in equal units, that is to say, luminosity is placed for convenience at 20 instead of IOO, and each successive square is [T][][][7] [*][7][7][ C[][][][] EH [...] [I] [I] [T] [T] DDDDD FIG. 19. just one unit deeper than the first trans- parent Square, so that square No. I passes the full amount of light, while square No. 20 passes none with normal exposure (see Fig. 19). In Fig. 20 is shown a representation of the solar spec- trum, with both Fraunhofer lines and Bunsen scale, and divided perpendic- ularly throughout its length by heavy IsochROMATIC PHOTOGRAPHY. 47 . 48 ISOCHROMATIC PHOTOGRAPHY. black lines which indicate the amount of the spectrum which each glass passes. With such a key before the eye there can be no possible error in the reading of the deposit, either in line, scale num- ber or Fraunhofer lines. In use the instrument is handled in the following manner: Suppose that it. is desired first to find the color sensitive- ness of a particular plate — for exam- ple, the Cramer Instantaneous Isochro- matic. A small size is taken (3% by 4%) and placed against the sensitom- eter in the darkroom in the same man- ner as in making a lantern slide, by contact, and exposed to light for a few seconds and then developed. It stands to reason that certain of the color squares, together with certain of the density squares, will show upon the plate, while certain others will be absent. Suppose that, after exposing and de- veloping a plate, we find a deposit upon squares 5, 6, 7, 8 and 9; we immediately know that the plate is sensitive to yel- low-green, blue-green, blue and blue-vio- let — the action which has taken place under square 8 being simply due to these colors, which, of course, exist in white light. If, however, the action was ISOCHROMATIC PHOTOGRAPHY. 49 shown only by a deposit on squares 2, 3, 4 and 8 then the plate would be sensitive only to the yellow, Orange and part of Seed 26 X. - I min. FIG. 21. the red, the action in square 8 again being due to the presence of these colors in white light. But it is not sufficient that the color squares shall only show a 50 ISOCHROMATIC PHOTOGRAPHY. deposit — that deposit must be correct. What about the luminosity? We may say that a plate is sensitive to pure yel- low, orange or red, but in what propor- tion is it thus sensitive — is it more strongly sensitive to the yellow than the red or vice versa? Stronger sensitive- ness is shown by a stronger deposit on a negative and on square No. 4 the de- posit may be twice as deep as on the other two, therefore, at first thought, it might be supposed that this was con- clusive, but it is not so; the luminosity of the color must be taken into account. Now, as we know, yellow has a lumi- nosity very much higher than orange or red; suppose we take the luminosity of this yellow as represented by ten units, while that of the red we may place at one, there being nine units difference between them; therefore, in judging the depth of deposits on these two squares we should have to make allow- ance for that variation before we would be able to make our deductions, entail- ing a vast amount of work before one could arrive at any reliable result, to say nothing of the photometrical apparatus necessary to make this deduction. Happily there is an easier and better l ISOCHROMATIC PHOTOGRAPHY. 51 way of arranging all this on the instru- ment itself. The seven colors have been measured by means of a photometer, Seed 26 X. 60 min. FIG. 22. and the darkest color of the seven se- lected as unit — in this case the blue. The other six are very much brighter 52 ISOCHROMATIC PHOTOGRAPHY. (or more luminous) than it, so one after another is compared with the blue, and their brightness (or luminosity) toned down, with a necessary amount of lamp- black in gelatin, until they are in perfect agreement with the unit blue. The red square, No. 1, requires the least amount of lampblack, while the yellow-red, No. 4, requires the most. Finally the white square is taken (No. 8) and gray is . added, until it, too, corresponds to the luminosity of the others. Of course this gives but the merest outline of the work necessary to reduce these nine squares to equality of brightness, and when finished each will appear dull and dingy in hue (simply because their luminosity is so low), but should they be placed in the path of a beam of very intense white light then they show in their purity. In ordinary light the square No. 8 (white) will look particularly dull, showing a very dark gray, but if the adjustment has been perfectly and conscientiously carried out there will be no error. The essential point is that each square must transmit nothing but the single band of color it is intended to pass — the green and blue must pass no red, nor the red any blue, nor must the colors overlap ISOCHROMATIC PHOTOGRAPHY. 53 greatly. Spectroscopic adjustment is an absolute necessity. Now, having all color squares reduced Ilford process plate. 4 min. FIG. 23. to equal luminosity, it is a simple thing to make a comparatively exhaustive test in a few minutes. Given a plate sensi- tive to all rays of the spectrum (were it 54 ISOCHROMATIC PHOTOGRAPHY. possible) it should, upon development, show a deposit on every color square. Greater sensitiveness to any particular region will be indicated by stronger de- posit upon the particular square cor- responding to that region. If it be desired to test any particular screen or ray filter all that is necessary is to first pass the light through the screen or filter before it strikes the sen- sitometer, and if the result is not satis- factory when the plate is developed it shows just what is wrong, and how to remedy this trouble. A perfect adjust- ment between screen and plate (for pure color) will be shown by an equality of deposit on each of the nine squares. If No. 7 (blue), for example, is not repre- sented on the negative then your screen cuts off too much of the blue and should be lightened, while if it shows too great a deposit upon the yellow then blue must be added to the screen. In short, when- ever a color shows too strongly it indi- cates the necessity for the addition of a dye complementary to the color out of adjustment, while if a square show a weak deposit or none at all it shows that a reduction is needed of the color com- plementary to the square in question. ISOCHROMATIC PHOTOGRAPHY. 55 It will be noted that I have stated that this is correct for pure color, but it does not follow that a filter perfectly ad- Cramer slow iso. - 3% min. FIG. 24. justed to this end will be correct for ordinary work, that is, landscape or gen- eral photography. On the contrary it would be decidedly wrong, for it must 56 ISOCHROMATIC PHOTOGRAPHY. be remembered that the colors in nature are not monochromatic or pure, but mix- tures, together with a certain amount of Hammer isochromatic. I min. FIG. 25. white light, allowance for which must be made in the filter. Thus a screen which would be correct for reflected “natural ” color would cut off the blue ISOCHROMATIC PHOTOGRAPHY. 57 square entirely in the sensitometer print, depending for the amount of deposit on the presence of that reflected white light just alluded to. Cramer inst. iso. - 45 Sec. FIG. 26. The instrument places in the hands of the tyro what is equal to an advanced education in photospectroscopy minus the time, apparatus and expense. It 58 ISOCHROMATIC PHOTOGRAPHY. would be folly for the non-scientific worker to attempt the manufacture of such an instrument, for an error in the Standard ortho. 1 min. - FIG. 27. - color transmission of any of the Squares would, of course, vitiate the value of the sensitometer. In making tests of various plates it is ISOCHROMATIC PHOTOGRAPHY. 59 absolutely necessary that they get the same amount of light action, not of ex- posure, for exposure and light action Seed L. ortho. - I min. - FIG. 28. - are not synonymous terms. We may expose a Cramer Slow Iso for two min- utes on a certain subject and then with exactly similar conditions expose an 6O ISOCHROMATIC PHOTOGRAPHY. Instantaneous Iso or a Seed 27 for the same time and get entirely different re- sults. The correct time for one would be wrong for the other. So that what Lovell C. D. - 45 Sec. FIG. 29 is wanted is equality of light action. If we give sixty seconds exposure to Cra- mer Slow Iso through the sensitometer and develop, we find, besides the color ISOCHROMATIC PHOTOGRAPHY. 61 patch deposits, certain others under the density (or exposure) Squares (I to 20) say, up to No. 12; then what is Carbutt polychromatic. I min. 30 Sec. FIG. 30. required is that when we make a test of the Cramer Instantaneous Iso, Seed Ortho, or any other plate, we shall, so expose that upon development under the 62 ISOCHROMATIC PHOTOGRAPHY. same conditions as at first we get deposit upon No. 12, thereby showing that the Cadett spectrum. 45 sec. FIG. 31. same amount of light action has oc- curred upon the plate. The writer is aware that this method of obtaining a light equality record is not scientifically correct. There is only ISOCHROMATIC PHOTOGRAPHY. 63 one method which is absolute, namely, by the use of a spectrographic instru- ment, for it is a fact that a certain make of plate will differ from another in its speed values simply because of a differ-, ence in color sensitiveness. However, for all practical purposes, the test as given by the sensitometer is sufficient. A word more about these latter squares. They also show the action or adaptability of a developer (or plate) to differentiation of each unit of shade, as represented by the varying thick- nesses of deposit, which conditions are best conducive to clearness and which to halation. (See illustrations, Figs. 21 to 31.) - . To the ordinary worker they serve to register the action of any particular anti- halation backing under extremes of light and shade, while to the color worker, or more advanced student, the color patches also stand as indicators of , the value of that backing in its adapt— ability to colorwork, while to all the ab- sence of deposit under any particular color square with the maximum of ex- posure” indicates the light transmitted * Maximum of normal exposure is hereby meant. 64 ISOCHROMATIC PHOTOGRAPHY. & yy by that patch as being a “ safe-light for development of the plate under test. Compare any of the illustrations throughout this chapter with the actual spectrum photographs which have pre- ceded them, and observe the extent of the absorption, while all the troublesome and vexing luminosity questions are forever laid at rest. Cadett spectrum plate and Cadett, “Absolutus" filter with twenty times normal exposure. ISOCHROMATIC. PHOTOGRAPHY. 65 CHAPTER VI. LIGHT FILTERs. We are now brought to the question of what screen to use and when to use it, and the problem is simplicity itself. It is necessary that a filter be used on every exposure made if correct action be desired. A certain amount of dis- crimination may be exercised in ordi- nary work, but it must be remembered that every departure from the perfectly adjusted filter means more or less of error in reproduction of color values. As I have before shown, it is not every or any yellow screen which will serve equally well for first-class results, but one must be adjusted carefully to the plate used. 4 To begin with, choose the plate which when unscreened shows the best ortho- chromatic effect, for it is impossible to make any isochromatic work without a thorough knowledge of the plate used, or, in other words, choose that plate 66 ISOCHROMATIC PHOTOGRAPHY. which shows greater sensitiveness to the various spectrum rays than another and make your screen (or filter) to suit that plate. Of course this adjustment must not be guessed at, and to the worker who is not the possessor of the necessary apparatus, no very close ap- proximate can be secured, but by a careful study of the spectrum or spectro- sensitometer prints which have illus- trated this series, a fairly good idea may be formed. It is to be regretted that the method of reproduction necessary in order to show these illustrations does not give full justice to the negatives. A great amount of the more delicate. detail, particularly in the case of the spectrum prints, is in this way lost. For example, in all of the unscreened spec- trum negatives the H and K lines at the extreme limit of the visible violet are very apparent, as are also many lines beyond, but they are impossible to show here. * Now, then, having chosen your plate you will very readily see that none of the so-called “ray filters” are exactly suitable, and as the manufacture is a very simple matter there is no reason why a palpably imperfect piece of appa- IsocFIRoMATIC PHOTOGRAPHY. 67 & - ratus be used when one can make for himself something that is better. In the first place, it must be taken into consideration that different effects . (in ordinary work) require different treatment, just as much as different strengths of light require different lengths of exposure, for the colors in nature are not pure colors, but are mixed with a considerable quantity of white light. It certainly stands to rea- son that with a plate sensitive to cer- tain colors the photographing of a bright midday landscape, with its blue sky and fleecy clouds, forms an alto- gether different kind of problem to that of an evening sky, with its gold and crimson and its reflected yellow glory over all the view. In the former there is the minimum amount of yellow with the maximum amount of the blue, violet and ultra-violet, while in the latter there is the maximum amount of yellow and the minimum of blue and violet, while the ultra-violet is considerably sup- pressed by the presence of the yellow reflected “ haze.” For one (unless we possess an adjusted filter) we must use a screen which will act strongly upon the blues and violets and weakly in the 68 ISOCHROMATIC PHOTOGRAPHY. yellows, while in the other it should be exactly the reverse. It is right here where careful adjustment is most neces- sary or the effect is overdone and the picture just as badly spoiled by the one . result as by the other. Every one has seen the reproductions which are scat- tered broadcast throughout the photo- graphic and other magazines, and the catalogues and pamphlets of the dealer, illustrating the advantageous" (P) re- sults which may be obtained by using So-and-so's ray filter, wherein the clouds are shown as so many balls of snow or chalk suspended in a pitchy sky in a manner that makes a person think the result would surely be fatal were they to fall on them. This is one of the re- sults of overcorrection of filter to plate. The blue has been reduced too much, therefore the sky-blue could not im- press itself sufficiently fast, the result being as has just been described. , , Of course it must be understood that. the use of a screen or ray filter upon any plate means a lengthening of the time of exposure. There is, however, an exception; for instance, a short time ago an amateur friend was explaining to the writer the particular advantages ISOCHROMATIC PHOTOGRAPHY. 69 of the screen used by him, and which required no lengthening of the time of exposure. Upon inquiry it was learned that the screen in use was composed of a dyed film of Hofmann violet, which 55 gave “most artistic effects * in the re- sulting negative. The user had never made any serious test between a view taken with and without that particular screen, but was very positive as to the improvement. Now the fact of the matter is that there was actually no difference in the negative made through this screen than that made with an ordinary plate, as the action of the violet was to cut out by absorption the very colors to which the plate (Cramer Iso) had been spe- cially sensitized, namely, yellow and yel- . low-green, and by the transmission of the blue-violet and ultra-violet had sim- ply, as before stated, brought the plate back to the condition of an undyed film. The user had, of course, made tests; of course he had made a negative through his filter (on an iso plate), and he had. also made one of the same subject with- out his screen (also using the iso plate), and when the writer ventured to sug- gest that he try one on an “ordinary” W 7O ISOCHROMATIC PHOTOGRAPHY. plate he was silenced by being told that iso plates were those which he always used, and it would be foolish to test on anything else. About one month later he woke up. - Here is the problem: Given a plat sensitive unequally to the various rays of the spectrum, so make your filter that it will hold back the colors which impress themselves too quickly, not cutting them off altogether, but dimming them down, and allow those that are photographic- ally weak to pass through unhindered. A glance through the many ‘spectra and sensitometer prints already shown will readily solve that problem, for there are given dyes that cut off any particu- lar ray desired, and by their judicious admixture in varying quantity any re- sult may be secured. For convenience (and the benefit of the beginner) I tabulate briefly a few of the principal dyes and their effect as filters upon the different hues of the spectrum. * Dye. Absorption. Picric acid . . . . . . . . . Napthol yellow . . . . . Aurantia . . . . . . . . . . . Auramin . . . . . . . . . . Metanil yellow . . . . . Acridin yellow . . . . . Eosin (yellow) ...... Eosin (blue) . . . . . . . Tropaeolin, O. O. O. Orange G. . . . . . . . . . . Coccinin . . . . . . . . . . . Ponceau . . . . . . . . . . . Biebrich scarlet . . . . . Saffronin . . . . . . . . . . . - Brasillin . . . . . . . . . . . Ruthenium red . . . . . Bordeaux red . . . . . . Magenta . . . . . . . . . . . Erythrosin . . . . . . . . . Part of the blue-violet and ultra-violet. Part of the blue-violet and ultra-violet. Part of the blue-violet and ultra-violet. Part of the blue-violet and ultra-violet. Part of the blue-violet and ultra-violet. Blue, violet and ultra-violet. - Green, blue, violet and ultra-violet. Green and blue. Green, blue and violet. Blue-green, blue and violet. • - Yellow-green, blue-green, blue, violet and ultra-violet. Yellow-green, blue-green, blue, violet and ultra-violet. Yellow-green, blue-green, blue, violet and ultra-violet. Greens and blue. - Yellow-green, blue-green and blue. Yellow-green, blue-green and blue. Yellow-green, blue-green and blue. Yellow-green, blue-green and blue. Yellow-green, blue-green and blue. S N Dye. - Absorption. Sudan III .......... Yellow-green, blue-green and blue. Crocin . . . . . . . . . . . . . Yellow-green, blue-green, blue and violet. Ammonium picrate . . . Blue, violet and ultra-violet. Emerald green . . . . . . Orange and violet. Malachite green . . . . Orange and violet. Solid green . . . . . . . . . Orange and violet. Anilin green . . . . . . . . . Orange and violet. Iodine green . . . . . . . . Orange and violet. Napthol green . . . . . . Red, orange, blue and violet. Light green S. F. ... Qrange and violet. Fast olive green .... |Orange and violet. Fast green . . . . . . . . . Orange, yellow and violet. Nile blue . . . . . . . . . . . Orange, yellow and green. Methylen blue ... ... | Orange, yellow and green. Methyl violet . . . . . ... Orange, yellow and green. Formyl violet . . . . . . . Orange, yellow and green. Crystal violet ....... Orange, yellow and green. Hofmann's violet ... Orange, yellow and green. ISOCHROMATIC PHOTOGRAPHY. 73 A very convenient method of manu- facturing a variety of screens suitable for use with the various plates upon the market is to coat thin sheets of Russian mica (which must be free from blem- ish) with a stained collodion. I have found this method very useful in work where a filter with a special action was desired for some particular plate or pur- pose. This stained mica may be used before, behind or between the combina- . tions of the lens, and one or more sheets may be introduced, at the will of the operator. The mica should be selected of as thin - a quality as is consistent with safe han- dling, and special care must be taken that no finger-marks appear on either surface. It is then cut up into pieces somewhat larger than the screen desired and flowed over with a collodion made as follows: . - t Gun cotton (Anthony's snowy)... Io grains Alcohol . . . . . • - - - - - - - - - - - - - - - - - - - I OU11}Ce . Ether . . . . . . . . . . . . . . . . . . . . . . . ‘. . . . I Ounce , Dye stuff (about). . . . . . . . . . . . . . . . 2 grains The dye should first be dissolved in the alcohol and the cotton then added. After standing for a few minutes the ether is added and the mixture shaken 74 ISOCHROMATIC. PHOTOGRAPHY. until the cotton is entirely dissolved, and then carefully filtered. The piece of mica is then edged with a solution of rubber in benzol (which dries almost immediately) placed upon a small piece of glass to give stability during the operation, flowed over with the stained collodion (only practice will give skill in this operation, but it presents no diffi- culties worth speaking of), gradually brought to a vertical position with a con- stant rocking semi-circular movement to avoid the collodion forming “waves,” and when set reared on end to dry. Several such screens may be made by selecting any dye from the foregoing list which will fulfill the necessary re- quirement of the conditions, or two or more differently stained sheets may be combined, as before stated. There is a slight loss of illumination in the ab- sorption of the mica, but it is so small that it can be overlooked. Any number can be carried into the field or from place to place between the leaves of a note-book. For screens of a lighter color dilute the collodion with equal proportions of ether and alcohol in vary- ing amounts. ISOCHROMATIC PHOTOGRAPHY. 75 It is impossible to give any more detailed instruction for manufacture without needless repetition of what has already been said, for if the earlier chap- ters’ have been seriously and carefully read they contain in themselves all the necessary information. First know what you are striving for — what color you want to cut out, or dim down, and then turn to the table of dyestuffs and select the color. In selecting a number of dyes for combination it is not sufficient that they give only the correct absorption; they must also pass without obstruction the rays that are desired. For example, suppose that it is required to cut off the yellow and the violet. A solution of chrysoidin and china-blue will do it, but a solution of methyl-blue and picric acid will do it better, for the first com- bination not only cuts off the undesir- able hues but also slightly dims down the luminosity of the greens, and it is for the determination of this latter point that the small prism (H, Fig. 2) is added. In use two equally luminous flames are used, one in front of the slit plate and the other at one side and care- fully adjusted for distance until upon 76 IsocFIROMATIC PHOTOGRAPHY. looking into the telescope the two spec- tra are seen, the one above the other, exactly coincident in luminosity, then the two solutions to be compared are placed one in front of each light, and the comparative absorption is seen at a glance. - - - . Although no really good or complete work in isochromatics can be performed without the aid of the spectroscope, yet visual observation of the spectrum is not enough, for the ultra-violet rays which are the most energetic in actinic effect are altogether invisible. For example: A solution or screen of chrysoidin yel- low appears to cut off the spectrum in the blue, and to totally absorb every- thing beyond, but a photograph taken through the same screen will show a strong action in the ultra-violet; hence the necessity for a photographic test be- fore making a deduction. - It is only a question of a very short time when the American plate manu- facturer will awake to the importance of following in the footsteps of his European brother, and make a filter and safe light suited to his own particular plate. The great army of photographers are becoming better educated in this line ISOCHROMATIC PHOTOGRAPHY. 77 . & with the passing of each year, until now the number of serious workers forms one vast concourse, which is just begin— ning to shake off the lethargy induced by “old-fashioned ” text-books that, in, many cases, still obtain as “standards.” Photographers are even now looking askance at many of the so-called iso- chromatic effects — a sure evidence of a higher education. But platemakers, like any other body of men, dislike a radical change, for it is so much easier to travel along in the rut worn smooth by usage than to make the effort to climb the side and “blaze" a new path, for- getful of the fact that a new path, if scientifically correct, will redound even- tually both to the honor and profit of the manufacturer. - * , In these chapters much detail work . has, of necessity, been omitted, but all salient points have been touched upon more or less fully, and the writer will be amply repaid if they are conducive in even a feeble way to the better under- standing of the subject, and hasten the time by even a fraction when the photo- graphic world will be educated up to and demand an isochromatic plate and filter that is truly isochromatic, and will not 78 ISOCHROMATIC PHOTOGRAPHY. be satisfied with any makeshift, however cheap or handy. - The writer is pleased to note that an absolute adjusted filter has been placed upon the market for both the Cramer and Seed Isochromatic plates. While Carbutt's filter is in many ways good for his polychromatic plate, yet in the hands of the author it has shown decided lack of adjustment, being over- corrected for the reds. NotE.- Since writing the above the author has been led to the conclusion that although the collodion methods serve very well for the manufacture of light filters which are not required to retain their permanency through a num- ber of years, yet the use of gelatin as a coating upon the glass is much to be preferred, as offering results which are to the best of his observation strictly permanent. After the lapse of a few years the collodion film is apt to show irregular opalescence (like ground glass), which interferes greatly with its working — in fact, it will, as it in- creases, render the screen entirely use- less. Under his continued observation for ISOCHROMATIC PHOTOGRAPHY. 79 a period of about eight or ten years, this defect has not shown itself with gelatin, therefore, for very careful work, the remedy is obvious. : MANUFACTURERS OF AND DEALERS IN PHOTOGRAPHIC APPARATUS, MATERIALS AND SUPPLIES OF ALL KINDS - The Anth0ly & SCOWill COIllpally * 122-124 Fifth Ave., New York ATALOGUE FREE PHOTOGRAPHY IN COLORS may be as far off as ever in actual accomplishment, but Photography of Colors is now rendered easy and certain by the use of the - FOR IsochRoMATIc PLATES A perfectly adjusted Ray Filter for use with and especially adjusted to the Cramer Iso. Plates, giving absolute luminosity, value of color, and crisp, clear negatives. A PERFECT HARMONY BETWEEN PLATE AND FILTER. SWIFTEST ABSOLUTE FILTER MADE. Mounted in nickel-plated cells, with springs or cork lining. The glass is optical “Crown” and perfectly parallel. Sizes to fit ordinary 4 x 5 and 5 x 7 Cameras, $1.50. Made in all sizes. BURKE & JAMES, Manufacturers of Photographic Apparatus and Supplies. 118 W. Jackson Boulevard, CHICAGO Branch Office: 1 to Fifth Ave., NEW YORK It's to Your Interest Mr. Photographer No matter how much or how little you buy, to keep in touch with us and our prices. We carry the largest stock of Photographic Supplies in the West, and are always prepared to give you the very best at the very lowest prices. Our stock is always complete in the way of new and up-to-date card mounts for both Amateur and Professional ; besides we are constantly turning out elegant designs from our own factory. We are sure we can interest you in Some way, so drop us a line stating your wants and we will gladly supply you with catalogues and prices. We always have something new and of interest to Photographers H. A. HYATT 410–12 N. Broadway - ST. LOUIS, MO. HAS NO DARK DAYS It prints by any light, yet requires no dark room for development. Velox gives pure black and white effects of surpassing depth and richness. NEPERA CHEMICAL CO., Division of the General Aristo Co. NEPE RA PARK, N. Y. For Jale by all TXealers. CRAMER's PLATES are the most perfect color-sensitive plates in the market. Made in three different grades of speed— Instantaneous — Medium — Slow We also make other brands, viz: Crown, Banner, Contrast, Non-halation, . X-Ray, Stripping, Lantern Slide, etc. Full descriptive catalogue to be had for the asking. Manufactured by G. Cramer Dry Plate Co. St. Louis, Mo. Offices in New York — Chicago–San Francisco Plain and Practical Books on Photography First Step in Photography Price, & 25 cents Second Step in Photography Price, tº º - 50 cents Photo-Beacon Exposure Tables Guaranteed correct. • * - Price, * … ( → tº 25 cents A Reference Book of Practical Photography Parts I and II. Price, each 50 cents Artistic Lighting - with chapters on ‘‘At Home Portraiture” by daylight and flashlight. Price, ſº - me gº 50 cents Amateur Portraiture at Home Price, * . ſº ſº 50 cents Pictorial Landscape Photography Price, - ſº tº- 50 cents The Photo-Beacon Co. 409 Security Building - Chicago Eastern Office: 621 Broadway, New York The Dime Series of Photographic Handbooks No. 6. PRice, 10 cents EACH Development, by Alfred Watkins Photographic Printing Processes, by Louis H. Hoyt . Beginners' Troubles, by J. Edgar Ross The Elements of Pictorial Composition, by F. Dundas Todd . Isochromatic Photography, by R. James Wallace My Photographic Experiments - by Ralph Martin The Photo-Beacon Co. 409 Security Building, - Chicago [ſiliili * SITY OF MICHIG A. ！！！！！！！！！！！！！！！！！： ： -·- . . . . . . . _ ---- | _ - _- -----|- -·|-· |-_|----- · _ |- -------. . . .|- · ·--· -|-------|-· -|-·|-· · - - - - _