•jrj +£ ^ 41 Nk*v A* m i «^ ; s»?f^ ►V V , ■?. "A. > " 'Al **Wl UNIVERSITY OF ILLINOIS LIBRARY Class Book ■&m& Volume IfJ l^Aty ■SSS Si w r ^* mm >M*: The person charging this material is re- sponsible for its return to the library from which it was withdrawn on or before the Latest Date stamped below. Theft, mutilation, and underlining of books are reasons for disciplinary action and may result in dismissal from the University. UNIVERSITY OF ILLINOIS LIBRARY AT URBANA-CHAMPAIGN NIVERSITY OF ILLINOIS BULLETIN Vol. VII. MARCH 7, 1910. No. 27 [Entered February 14, 1902, at Urbana, Illinois, as second-class matter under Act of Congress of July 16, 1894. ] BULLETIN No. 12 DEPARTMENT OF CERAMICS A. V. BLEININGER, Director NOTES ON THE MANUFACTURE OF ENAMEL BRICK WITH SOME INVESTIGA- TIONS ON ENAMEL BRICK SLIPS BY R. T. STULL, Urbana, III. 1909-1910 PUBLISHED FORTNIGHTLY BY THE UNIVERSITY [Rei-rinted from Transactions or American Ceramic Society, Vol. XII. Paper read at Pittsburgh Meeting, Febiuary, 1910] NOTES ON THE MANUFACTURE OF ENAMEL BRICK WITH SOME INVESTIGATIONS ON ENAMEL BRICK SLIPS. BY K. T. Stull, Urbana, 111. Aside from the contribution by Barringer in Volume V of our Transactions, very little literature can be found of material assistance to the prospective manufacturer of enamel brick. Although the fundamental principles of ceramics apply to the manufacture of enamel brick, they have not been clearly pointed out in this line of business; besides, there are problems peculiar to the trade which need more thorough investigation. The majority of men in America, who are in charge of the manufacturing end, are of foreign birth. They have brought their experiences and recipes with them, and have gone through the painful experiences of applying them to our conditions. This has been largely responsible for the prevailing belief that "we must go abroad to get clays for our slips."" If all Pkirope should pass stringent laws prohibiting the exportation of her clays, it is not probable that the American white ware potters and enamel brick makers would go out of business, nor make anjr great sacrifices in the quality of their products. Clays suitable for enamel brick bodies should possess low shrinkages, good bond, be free from warping and cracking, stand up well at cone 4 or higher, and burn to a light color comparatively free from iron spots. The plastic fireclays are well suited to this purpose. It is quite essential, however, to reduce their shrinkages by the addition of flint clay or grog. The majority of body mixes vary from GO to 80 plastic and -10 to 20 non-plastic * Instead of "engxjbe" the writer prefers to use the word "slip" because it is the term universally understood by enamel brick makers. 3 4 ON THE MANUFACTURE OF ENAMEL BRICK. parts. Some clays will carry a small percent of sand without material injury. Oue mixture which has been in use for several years is composed of 70 parts plastic clay, 20 parts grog, and 10 parts crushed sand stone. METHODS OF MANUFACTURE. In general, two different processes of manufacture are recognized, viz., one fire and two fire. In both one and two fire ware, the methods of applying the veneer are practically the same, the distinguishing feature being that, in the two fire process, the brick are first biscuited at a low temperature before the veneer is applied. Quite recently mechanical appliances have been introduced which promise to make some radical changes in the manu- facture of enamel brick. For the present work, the meth- ods of manufacture will be divided into two general groups, according to the methods of application of the veneer. I. Hand Dipping Process. (a) Single Fire: 1. Dipping Stiff Mud Brick, 2. Dipping Leather Hard Brick, 3. Dipping Bone Dry Brick. (b) Two Fire:" 1. Dipping Biscuited Brick. II. Mechanical Veneering Process. (a) Single Fire: 1. Veneering Stiff Mud Column and Wire Cutting. A favorite method of making enamel brick in Europe is by dipping a stiff-mud wire-cut brick. The face of a iirst quality enamel brick must be as near perfect as it is possible to make it. Since the brick are not repressed, the die is watched with the greatest care, and frequently lined up to normal size in order to take up the wear. It is important that the brick be cut straight. A method in vogue is to cut the column into blocks which ON THE MANUFACTURE OF ENAMEL BRICK. 5 are dipped, and after the slip has hardened sufficiently, the blocks are "squared" on a hand cutting table. This is also an effective way of removing the excess slip on the sides. Although this method has not been exploited to any extent in America, it has many advantages well worth investigating : 1. Repressing and consequent flaking of the slip due to oil on the surface are avoided. 2. There is a better bond between slip and body since the two shrink together in drying. 3. The necessity of storing the brick until they reach leather hard consistency is eli- minated. In the leather hard method, the brick are allowed to harden by partial drying until nearly all drying shrinkage has ceased before they are dipped. The brick may be formed on a soft-mud machine, or "slush'' molded by hand in wooden molds, hardened down to a stiff -mud consistency and re-pressed, or, more commonly, made stiff mud on a plunger or auger machine, wire cut, and re-pressed. Owing to the variation in size and shape, the soft-mud machine method is to be recommended only where two grades of brick are to be made. By sorting the brick as they come from the repress, those which are true in form and size can be used for enameling and the remainder burned for builders. The process of slush molding and repressing by hand is very similar to that for hand made fire brick, except that more care is taken in filling and dumping the molds and greater care exercised in repressing. The advantages in repressing are that the brick can be "squared up," panelled and the firm's name stamped on the side. With the stiff-mud brick not subjected to the repress, the brick can be judiciously cored and the lettering stamped on the back side of the column by a roller. A few plants are glazing bone dry brick. Although sold as enamel brick in some cases, they are in reality 6 ON THE MANUFACTURE OF ENAMEL BRICK. nothing more than glazed brick, and should be classed as such. To the writer's knowledge, there is not a plant at the present time successfully making a white enamel brick by dipping a bone dry body in slip and glaze. It is doubt- ful whether this method will ever be a success owing to difficulties encountered in cracking ami flaking of the slip. In the two fire process the brick may be made soft- mud repress, stiff-mud wire-cut, stiff-mud repress or dry- press process. The brick are first biscuited at heats rang- ing from cone OS to cone 01, then dipped in slip and glaze and given the glost fire at cones 3 to 9. A few plants mak- ing dry pressed front brick from fire clays are enamelling their culls, which are too soft for the market or off in color but otherwise having true faces. Methods of Dipping-. In some cases the brick are given one dip in the slip and one in the glaze, but in most cases the brick are given two dips in the slip and one in the glaze. A factory which has been brought to the writer's notice sprays on the first coat and dips the second one. Two slips of different com- position are sometimes employed, the first dip being made in a slip comparatively high in ball clay and correspond- ingly low in China clay or kaolin. Over this a second coat is applied composed of materials giving a much whiter surface. The thickness of the slip is an important factor. It is essential that it be applied thick enough in order to form a smooth coating and to hide the character of the body underneath. In the two fire process the brick may be porous enough to take on a sufficient coating in one dip, but for stiff-mud and leather-hard bodies, one dip is seldom sufficient, except in cases where a more or less opaque glaze is applied over. The proper thickness of the slip under ordinary conditions is from three-hundredths to five-hundredths of an inch. Where the slip is thin, the ON THE MANUFACTURE OF ENAMEL BRICK. 7 differences in shrinkage and expansion of body and slip are balanced by the elasticity of the slip, thus preventing rupture. If the coating of slip is too thick, its shrinkage and expansive forces may cause cracking, crazing or flaking. The glaze applied over the slip should be quite viscous so as to prevent excessive flow and beading along the edges, and to overcome the absorption of the glaze by the slip and the consequent vitrifying of the slip which would cause the dark color of the body to show through. Defects Appearing After Dipping. The principal defects which appear after dipping be- fore the brick enter the kiln are: 1. Pinholes. 2. Flaking. 3. Cracking. J'inholcs. Pinholes may occur from four causes: 1. Using a freshly made slip. 2. Pinholes or cavities in the surface of the brick. 3. Dust on the face to be dipped. 4. Bad dipping. The writer has seen pinholes appear repeatedly by dipping brick in a freshly made slip. After ageing the slip for a short time, pinholes from this cause disappeared. A week's ageing of the slip is usually sufficient. After dipping, the pinholes do not appear until the "water gloss" of the surface begins to disappear. Bubbles which appear on the surface break, leaving small cavities in the surface. 2. Air is entrapped in small cavities or pores in the dipped surface. As the water in the slip is absorbed by the brick, the air in these small cavities is forced out, passing up through the slip, thus causing pinholes. 3. In dipping a dusty surface, air is entrapped in films around the dust particles and in cavities between g ON THE MANUFACTURE OF ENAMEL BRICK. them. As the water in the slip slowly creeps over the surface of these particles, the air is released and rises to the surface. In order to overcome pinholes caused by dust or minute cavities in the surface, brick makers resort to "scrubbing;" i. e., the surfaces to be eDameled are brushed over with a stiff brush dipped in water, or more commonly, in a slip diluted with water. Other recipes which have been in use are : water, slip and glue ; water, slip and molasses; water, fire clay and white slip. 4. Air may be entrapped by bad dipping. This oc- curs if a flat surface of the brick meets the surface of the slip when first immersed. A good method of dipping is to hold the back of the Itrick in the palm of the hand with face to be dipped, down. By allowing one edge of the brick to first meet the surface of the slip as in position 1, the slip is washed across the face by a rocking motion through 2 to 3. Then by the reverse motion (without removing the brick from the slip), the brick is passed back through 4 to 5. The end of the brick farthest from the operator is then raised as in posi- tion 6, which allows the excess slip to run down the edge and leave at the corner as it is raised from the slip. The brick is then quickly inverted and slid onto a bench. The clipping should be done by an easy swinging mo- tion to and fro without a halt in the operation. The time required for a single dip is from three to six seconds, and a careful dipper can perform the operation alternately right and left handed, getting very little slip over the edges. ON THE MANUFACTURE OF ENAMEL BRICK. "RAINS'. ArV.CE-R. SOC. VOL. XII. / \ Z <- DiHererrt Positior\s05 BricMn Dipping- Flaking. Flaking or shelling of the slip is due to lack of bond. It may occur soon after dipping or may not appear until the brick are subjected to the fire. Lack of bond may be caused by oil or dust on the surface, or by unequal shrink- age of slip and body. It is most frequently caused by too low shrinkage of the slip, but in some cases it is caused by too high shrinkage of the slip. In the latter case crack- ing and flaking will appear on the same surface. Scrubbing the surface before clipping not only pre- vents pinholes, but also assists adhesion by removing dust and oil which may cause an otherwise good slip to flake. Slips too low in plastic clay, or slips too high in kaolin or China clay which are short or weak in character will cause flaking. Where flaking is due to low shrinkage, the remedy is to increase the percent of plastic clay and de- 10 ON THE MANUFACTURE OF ENAMEL BRICK. crease the non-plastic portion. Where cracking' and flak- ing occur, reduce the percent of clay and substitute part ball clay for China clay or kaolin. The tendencies of ball clay are to increase shrinkage, impart greater adhesive power and render the slip more yielding or ductile by which it adjusts itself better to the brick, thus preventing rupture. Some English recipes for slips require plaster of paris to overcome flaking. It is necessary in such cases to exer- cise care in burning, besides, the cause of rough, blistered and scummed glazes can frequently be traced to plaster in the slip. The use of plaster to prevent flaking is unneces- sary, since good reliable slips can be had without it. Cracking. Cracking may be caused by: 1. Excessive shrinkage of the slip. 2. Too thick a coating of slip. 3. Too fine grinding of slip. 4. In dipping leather hard, allowing the brick to become too dry before dipping. 5. Using clays which are weak or have low tensile strength. Cracking may be overcome by substituting a clay of low shrinkage for one of higher ; or increasing the non- plastic portion and decreasing the plastic part, such as increasing flint and feldspar or Cornwall stone, or replac- ing part raw clay with calcined clay. Blunging the slip instead of grinding is to be recom- mended. The use of a small quantity of carbonate of soda or borax is found to be beneficial to overcome cracking. The proper amounts of these soluble materials to use is an important factor and varies in different slips, hence the amount should be determined experimentally. Slips high in clay require more than slips low in clay. Mechanical Methods of Applying Slip. The most universal method of applying slip and glaze is by hand dipping and removing the surplus on the sides by scraping with a knife or scratching with a fine wire brush. Quite recently a leading enamel brick plant has ON THE MANUFACTURE OF ENAMEL BRICK. 11 been experimenting with a dipping machine similar in construction to that used for dipping wall tile. The ma- chine is made somewhat larger, with a few minor changes in its construction in order to make it more suitable for its new purpose. The automatic veneering process is one which has a great future. The process consists in veneering a column of stiff mud clav after it issues from a die. For this pur- pose a veneering device is attached to the end of the die or placed in front of it for spreading the slip in a layer about one-sixteenth of an inch thick upon the faces to be veneered. Although there are four American patents on devices for veneering a column of clav, but one of these seems to be successful for the manufacture of enameled brick, viz., the Ramsay patent, which has recently been brought to public notice by an infringement suit. The veneering device consists of two rectangular frames A and B, called slickers, having two plates between as C, one at each side. These slickers are fastened to- gether by two bolts at each side as DD. The apparatus is supported by the die and about one inch in front of it on two rods E, one at each side. Figs. 2 and 3 represent the apparatus rigged for making stretchers, in which case the top of the column is veneered. Fig. 4, a vertical sec- tion across the column, shows the arrangement for making quoins, in which case the top and one side of the column are veneered. The same principle is used for making bull nose and other shapes. "A" is the surface preparing slicker having the same inside dimensions as the delivery end of the die. "B'' is the slip slicker and is five sixty-fourths of an inch larger than the surface preparing slicker at all points where the slip is to be applied to the column. "S," the slip which is pugged to about the same consistency as clay userl for pressing white ware, is placed upon the column between A and B. As the column moves forward the slip adheres 12 ON THE MANUFACTURE OF ENAMEL BRICK. TRANS. AM CE f?. S>OC. VOLXII. 5TULL. SVdeM\evt S\\ov*'vftc^tiAe\V\o4 OS Meneev'wx^To? Q* Co\un\n. N. A— P. ?^A End\T\e>w SV\ow'm^N\e\Y\od OS - \jeneer'm^Topi\t\dS\Ae05Co\vAmi\. OX THE MANUFACTURE OF ENAMEL BRICK. 13 to it and rolls over and over, unwinding as it were, and is spread in a coating about one-sixteenth of an inch in thickness by the slip slicker "B." The column is cut into brick on a hand cutting table of special design and dried on a hot floor. The bricks are loaded on trucks and the glaze applied by a large sprayer having the air and glaze under a pressure of forty to sixty pounds. The brick are then set and burned single fire. Setting. Of the three methods of burning, viz., open fire, burn- ing in muffles and burning in saggers, the open fire method is most economical but requires considerable care and skill in setting. Some brick makers set the brick in piers, but the writer prefers setting in benches extending across the kiln. In two fire ware the brick may be set on the flat as described by Barringer, 1 but for single fire ware this method causes considerable loss in cracking owing to shrinkage. In order to overcome this difficulty, the stretchers on the outside of the benches are set on end and shapes set flat in the middle in piers, (Fig. 5). In the single fire method the brick should go into the kiln bone dry. In the writer's experience, brick which Avere set wet frequently came out with a dry, rough sur- face as though the glaze were underfired. At other times the glaze would be blistered or badly scummed. These brick were called by the workmen "steamed brick." Re- peated burning of these brick made no appreciable differ- ence in their appearance. It is probable that these brick being wet, took up sulphur dioxide from the kiln gases, which in turn oxi- dized to sulphuric acid. This naturally would combine with lime and zinc oxide present in the glaze, and since the kilns were burned oxidizing throughout, the sulphates would naturallv remain as such. 1 Trans. A. C. S., Vol. V, p. 273. 14 ON THE MANUFACTURE OF ENAMEL EHICK. TRANS. AM CER.SOC. VOLXII. PotWcm o?r BencK } C^uo\n5 m a tV\eNUdd\e, Stve\cV\ers QoAs\de. INVESTIGATIONS BY THE WRITER. (Ceramic Laboratory, University of Illinois) The following" work comprises sonic investigations on enamel brick slips applied to leather hard, bone dry and biscuit bodies between the limits 25 to 75 parts clay materials, 75 to 25 parts non-plastic materials. The ceramic materials employed were: Georgia kaolin, North Carolina kaolir, Tennessee ball clay (No. 1), Brandy wine feldspar, Ohio flint (8 hr. grind), M. G. R. English China clay, ON THE MANUFACTURE OF ENAMEL BRICK. 15 Pikes English ball clay (No. 20), English Cornwall stone, Carbonate of soda. The objects of the work were to determine the range of good slips within the above named limits, to study the causes and remedies of defects, and to compare the slip making values of some of the English materials with those of a few American materials. If a brick is to come from the kiln as a No. 1 article, it must first enter the kiln in No. 1 condition. The first step undertaken in the work was, to determine the ratios of plastic to non-plastic portions for slips which would fit the bodies perfectly in dipping, and which were to be used as bases for making the slips for the burning trials. For this purpose series 27, 28, 20 and 30 were constructed. Carbonate of soda was kept constant at one percent in all slips throughout the work. All slips contained ten percent of ball clay, two different ball clays being em- ployed for comparison. The slips were weighed dry, blunged, passed through a 100 mesh screen, set at 1500 to 1520 B & L hydrometer, and placed in sealed jars and allowed to age for one week. The body for the briquettes was composed of TO parts plastic fire clay and 30 parts 16 mesh grog. The trials were made stiff mud on a small auger machine and wire cut. The trials received two dips in the slip, the dipped surface first being scrubbed with two parts water and one part of the slip to be applied. it; ON THE MANUFACTURE OF ENAMEL BRICK. SERIES 27. Ga. Kaolin— No. 1 Tenn. Ball. No. Kaolin Tenn. No. 1 Ball. Flint Car- bonate of Soda On Leather Hird On Bone Dry On Biscuit Basis for Series 185 186 15 25 35 45 55 65 10 10 10 10 10 10 75 65 55 45 35 25 1 1 1 1 1 1 Flaked Flaked Flaked Cracked Cracked Cracked Cracked Flaked Flaked Cracked Cracked Cracked Cracked Cracked Good Cracked Cracked Flaked Cracked Cracked Cracked 31 and 50 187 188 189 190 In series 27 all slips flaked on leather hard trials, and flaked and cracked on bone dry. Slip No. 185, containing 15 Georgia kaolin and 75 flint, was good on biscuit. This slip was selected as the basis for Series 31 and 50. All other slips cracked and flaked. SERIES 28. N. C. Kaolin— No. 1 Tenn. Ball. ' N. C. Kaolin Tenn. Car- on On No. No. 1 Flint bonate Leather Bone On Biscuit Basis for Series Ball of Soda Hard Dry 191 15 10 75 1 Flaked Flaked Good 32 and 51 192 25 10 65 1 Flaked Flaked Good 33 and 52 193 35 10 55 1 Flaked Flaked Good 34 and 53 194 45 10 45 1 Flaked Flaked Good 35 and 54 195 55 10 35 1 Flaked Flaked Good 36 and 55 196 65 10 25 1 Flaked ! Flaked Good 37 and 56 ! In Series 28 all slips fit perfectly on biscuit but flaked on bone dry and leather hard bodies. SERIES 29. N. C. Kaolin— English Ball. No. N. C. Kaolin English Ball Flint Carbon- nate r.f Soda. On Leather Hard On Bone Dry On Biscuit Basis for Series 197 15 10 75 1 Flaked Good Good 38 and 57 198 25 10 65 1 Flaked Good Good 39 and 58 199 35 10 55 1 Flaked Good Good 40 and 59 200 45 10 45 1 Flaked Doubtful Good 41 and 60 201 55 10 35 1 Good Cracked Good 42 and 61 202 65 10 25 1 Good Cracked Good 43 and 62 ON THE MANUFACTURE OP ENAMEL BRICK. 17 Series 29 is the same as Series 28 except that Pikes No. 20 English ball clay replaces Tennessee ball. In this series all slips work perfectly on biscuit, the three lowest in clay fit bone dry, the others cracked. The two highest in clay fit perfectly on leather hard. SERIES 30. English China — English Ball. No. Knglish Cm na English Ball Flint Carbon- ate of Soda On Leather Hard On Bone Dry On Biscuit Basis for Series 203 15 10 75 1 Flaked Good Good 44 and 63 204 25 10 65 1 Good Good Good 45 and 64 205 35 10 55 1 Good Cracked Cracked 46 and 65 206 45 10 45 1 Good Cracked Cracked 47 and 66 207 55 10 35 1 Good Cracked Cracked 48 and 67 208 65 10 25 1 Good Cracked Cracked 49 and 68 Slips containing 15 to 25 China clay were good on biseuil and bone dry, the remainder cracked. The slip lowest in clay flaked on leather hard, the remainder were good. Limits of Plastic and Non-Plastic for Dipping. Selecting all slips which are good in the above four series, we find that for leather hard, perfect fitting slips in dipping lie within the range: Clay 35 to 75 Non-plastic 65 to 25 For dipping bone dry: — Clay 25 to 45 Non-plastic 75 to 55 For dipping biscuit: — Clay 25 to 75 Non-plastic 75 to 25 Undoubtedly slips higher in clay would dip well on leather hard trials, but these were considered as imprac- tical on account of crazing after burning, as will be shown later on. 18 ON THE MANUFACTURE OF ENAMEL BRICK. Slips lower in clay would probably clip perfectly on biscuit, and here again we find crazing. After determining the limits of plastic and non- plastic portions for perfect fitting slips in dipping, the next step in the work was to select each of the perfect working- slips as a basis of a series in which the non-plastic portion was varied between flint and flux. Series 31 and 50 are the only two containing Georgia kaolin which dipped well on biscuit. The other series are arranged in six groups, the flux in the first three being feldspar. The other three groups are a repetition of the first three, except that Cornwall stone was used as the flux in place of the feldspar. Three different burns were made, viz., cones 4, 6 and 8. The variation in the kiln was such as to give cone 2 in the coolest part of the cone 4 burn, and cone 9 in the hottest part of the cone 8 burn. Trials were set on edge in tile saggers. Three trials of each slip were placed in each burn, two having glaze No. 5 1 applied over and the third slip left unglazed. Cones were also placed in each sagger. A portion of each slip was cast ^4 x y 2 x 1% inches in plaster molds. These cast trials Avere placed in the saggers with the dipped trials and used for determining the poros- ity of the slips. It was desirable to know what relation porosity had to the ability of slips to stand the freezing- test. This part of the work is under way and not com- pleted at the present writing. 1 Trans. A. C. S., Vol. X, p. 21S. ON THE MANUFACTURE OF ENAMEL BRICK. 19 SERIES 31. (On Biscuit) No. Constant Flint Spar Cone 5 Cone 7 Cone 9 L-J O — 209 60 15 Crazed Crazed Crazed 210 • y-i -Q 55 20 Crazed Crazed Crazed 211 : o 50 25 Crazed Crazed Crazed 212 : £ «-i 45 30 Crazed Crazed Crazed 213 o 40 35 Crazed Crazed Crazed 214 £%2 35 40 Crazed Crazed Crazed 215 Kao n. B bona 30 40 Crazed Crazed Crazed 216 25 50 Crazed Crazed Crazed . s - ci v d CrC All are good smooth slips but crazed. The glaze tends to decrease crazing of the slip. Crazing of slip increases with increase in temperature. Crazing decreases with re- placement of flint by feldspar. No. 209 is a beautiful white, the whitest slip in the entire work. Group I — Series 32 to 37. SERIES 32. (On Biscuit) 217 218 219 220 221 222 223 224 • 33 O Z rj 45 20 Good Good Good 227 O 40 25 Good Good Good 228 35 30 Good Good Good 229 .So 30 35 Good Good Good 230 2 ^ . Constant Flint Spar Cone 6 Cone 7 Cone 9 24s in © iH rH H ~ 30 5 Good Good Good 249 O 25 10 Good Good Good 250 £ 20 15 Good Good Good 251 .= ' ' o 15 20 Cracked Cracked Cracked 252 §-3 2 10 25 Cracked Cracked Cracked 253 N. C. K Tenn. B Carbona 5 30 Cracked Cracked Cracked This series is similar to Series 35. The cracking, how ever, is a little more prominent. 22 ON THE MANUFACTURE OF ENAMEL BRICK. SERIES 37. (On Biscuit) Constant: N. C. Kaolin, G5; Tenn. Ball No. 1, 10; Carbonate of Soda, 1. No. Flint Spar Cone 3 Cone 6 1 Cone S Unglazed 1 Glazed Unglazed I Glazed / Unglazed | Glazed 254 20 5 Cracked Crazed Cracked Good Cracked Cracked 255 15 10 Cracked Crazed Cracked Good Cracked Good 256 10 15 Cracked Crazed Cracked Crazed Cracked Good 257 5 20 Cracked Crazed Cracked Crazed Cracked Good 258 25 Cracked Crazed Cracked Crazed Cracked Good All slips cracked. Glaze tends to prevent cracking of slip. Slips did not craze, but glazes crazed over slips in fine zig-zag lines. Increasing temperature of firing de- creases crazing of the glaze. The six different groups were plotted on tri-axial dia- grams. In many cases the unglazed slips were defective and the same slips glazed were good. Only those slips were plotted as good which were sound both glazed and unglazed, and all such slips that were sound at one tem- perature, but may have been slightly defective at some other temperature, were plotted as good. Slips which were translucent (due to vitrification) but otherwise perfect were also plotted as good. ON THE MANUFACTURE OF ENAMEL BRICK. 23 TRANS. AM.CER. SOC. VOL. XII. Group I. NX. Kaolin - 15 to 65 Brandywi7ie6/?cm5to50 Oftio8ffr.nint~0tb60 Cons tants Afot Plotted § TermBallNo./ ~/o Ca r ton ate Soda& -/ ^ Clay A ■ Good On Biscuit K = Craved » » C = CvacKed » » + = dli/is That O id Not Craze 0^ fr But Over Wnich Glajecrajed. cX" Conclusions on Group I. Grazing \ A high content of flint evidently causes crazing of the slip. Decreasing flint and increasing clay or feldspar, or both, decreases crazing. Increasing clay is more effective in overcoming crazing than increasing feld- spar. With flint constant, decreasing clay and increasing feldspar, increases crazing. Crazing of the slip increases with increase in burning temperature. A high content of clay does not cause the slip to craze, but causes the glaze applied over the slip to craze. De- creasing clay and increasing flint or feldspar, or both, in the slip decreases crazing of the glaze. Increasing the burning temperature decreases glaze crazing. Cracking : Excessive clay in the slip causes cracking during burning. Decreasing clay and increasing flint or 24 ON THE MANUFACTURE OF ENAMEL BRICK. feldspar, or both, decreases cracking. Increasing flint de- creases cracking more effectively than increasing feldspar. With clay constant, decreasing flint and increasing feld- spar increases cracking. Good slips in this group on a biscuit body are found between the limits : Georgia Kaolin 15 to 55 Flint 10 -to 50 Feldspar 5 to 50 Ball Clay 10 J Constant Carbonate of Soda 1 \ Group II. Series 38 to 43. SERIES 38. (On Biscuit) Const mt: N. C. Kaolin, 15; English Ball , 10; Carbonate of Soda. 1. 1 Cone 3 Cone G Cone 8 No- Flint Spar Unglazed l Glazed Unglaze.d Glazed Unglazed Glazed 2 : 9 GO 15 Crazed Crazed Crazed Crazed Crazed Crazed 2«0 55 20 Crazed Crazed Crazed Crazed Crazed Good 261 5(1 2o Crazed Crazed Crazed Good Crazed Good 26 -1 45 30 Crazed Crazed Good Good Crazed Good 263 40 35 Good Good Good Good Crazed Good 264 35 4d Good Good Good Good Crazed Good 265 HO 4o Good Good Good Good Crazed Good 266 25 50 Good Good Good Good Crazed Good 267 20 55 Good Good Good Good Crazed Good Crazing of unglazed slips increases and crazing of glazed slips decreases with increase in temperature. Graz- ing decreases with increase in feldspar. Aside from craz- ing, slips fit perfectly. Slips 264 to 207 are translucent at Gone 6, due to vitrification. Slips 201 to 207 are translu- cent at Cone 9. ON THE MANUFACTURE OF ENAMEL BRICK. 25 SERIES 38. (On Bone Dry) No, Cone 3 Cone 5 Com s Unglazed I Glazed Unglazed I Glazed Unglazed Glazed 259 Crazed Cracked Crazed Crazed Cracked Crazed Crazed Craeked Good 260 Crazed Cracked Crazed Crazed Cracked Good Crazed Cracked Good 261 Crazed Cracked Crazed Crazed Cracked Good Crazed Cracked Good 262 Crazed Cracked Good Crazed Cracked Good Cracked Good 263 Crazed Good Crazed Cracked Good Good ? Good 264 Crazed Good Cracked Good Cracked Good 265 Good Good Cracked Good Good ? Good 266 Good Good Good Good Good ? Good 267 Good Good Good Good Cracked Good Slips show a tendency to crack. Cracking does not seem to be influenced by variation in composition or heat treatment. Cracks extend down into the body about 1/32 to 1/16 of an inch. SERIES 39. (On Biscuit) Const Hit N. C Kaolin, 25; En glish Ball, 10; Carbonate of So da, 1. Con e 4 Cone 6 Cone 3 No Unglazed Glazed Unelazed I Glazed Unglazed | Glazed 268 50 15 Good Good Good Good Cracked Good 269 45 20 Good Good Good Good Cracked Good 270 40 25 Good Good Good Good Cracked Cracked 271 35 30 Good Good Good Good Good Good 272 30 Rfi Good Good Good Good Good Good 273 25 40' Good Good Cracked Cracked Cracked Cracked 274 20 45 Good Good Cracked Good Good Good 275 15 50 Good Good Cracked Good Good Good Slips have a slight tendency to crack, which increases with increase in feldspar and temperature. Glaze over the slip tends to prevent cracking. (See Pig. 6). All slips are opaque at Cone 6. Slips 272 to 275 are vitrified and translucent at Cone 8. 26 ON THE MANUFACTURE OF ENAMEL BRICK. TRAN5.AM-CER. SOC. VOL. XII. 5TULL ILLUSTRATIONS OF GLAZE PREVENTING SLIPS FROM CRACKING. SERIES 39. (On Bone Dry) No. Cone 4 Cone 6 Cone 8 Unelazed | Glazed Unclazed I Glazed Unglazrd | r:laze4 268 Cracked Good Cracked Cracked Cracked Cracked 269 Cracked Good Cracked Good Cracked Good 270 Cracked Cracked ('racked Cracked Cracked Cracked 271 Cracked Cracked Cracked Cracked Cracked Cracked 272 Cracked Cracked Cracked Good Cracked Cracked 273 Cracked Cracked Cracked Cracked Cracked Cracked 274 Cracked Cracked Cracked Cracked Cracked Cracked 275 Cracked Cracked Cracked Cracked Cracked Cracked Cracking quite bad; worse than series 38. ON THE MANUFACTURE OF ENAMEL BRICK. SERIES 40. (On Biscuit) 27 Constant: N. C. Kaolin, 35; English Ball, 10; Carbonate of Soda, 1. No. Flint Cone 4 Spar 1 1 Unglazed 1 Glazed Cone 6 Cone 9 Unelazed I Glazed Unglazed I Glazed 276 277 278 279 280 281 282 283 45 10 Cracked Cracked 40 15 Cracked Cracked 85 20 Cracked Cracked 30 2."> Cracked Cracked 2fi 30 Cracked Cracked 20 35 Cracked Cracked 15 40 Cracked Cracked 10 45 Cracked Good Cracked Cracked Cracked Cracked Cracked Cracked Cracked Cracked Cracked Cracked ; Cracked Cracked Cracked Cracked Cracked Cracked Cracked Cracked Good Cracked Cracked Cracked Good Cracked Cracked Cracked Cracked Cracked Cracked Cracked Cracked Good Cracking of slips very bad. Cracking decreases with increase in feldspar. Glaze tends to prevent cracking of the slip. All slips are opaque at Cone 4. Slips 281 to 283 at Cone 6, and 279 to 283 at Cone 9 are vitrified. SERIES 40. (On Bone Dry) 276 Cracked Cracked Cracked 277 Cracked Cracked Cracked 278 Cracked Cracked Cracked 279 Cracked Cracked Cracked 280 Cracked Cracked Cracked 281 Cracked Cracked Cracked 282 Cracked Cracked Cracked 283 Cracked Cracked Cracked All slips both glazed and unglazed crack badly. Crack- ing extends through slips into the body. 28 ON THE MANUFACTURE OF ENAMEL BRICK. SERIES 41. (On Biscuit) Constant: N. C. Kaolin, 45; English Ball, 10; Carbonate of Soda. 1. Flint Spar Cone 5 Cone 7 Cone 9 Unglazed I Glazed Unglazed | Glazed Unglazed I Glazed 284 35 10 Cracked Good Cracked Good Good Cracked 285 80 15 Good Good Cracked Good Good Good 286 25 20 Good Good Cracked Cracked Cracked Cracked 387 20 25 Cracked Good Cracked Good Cracked Good 288 lfi 30 Good Good Good Cracked Good Good 289 1U 35 Cracked Cracked Cracked Good Cracked Cracked Slips which cracked showed a tendency to curl up and flake. All slips are opaque at Cone 9. SERIES 42. (On Biscuit) Constan : N. C. Kaolin, 55; English Ball, 10; Carbonate of Soda, 1. Cone 5 Cone 7 Cone 9 Flint Spar Unglazed | Glazed 1 Unglazed I Glazed Unglazed | Glazed 290 30 5 Cracked Good Cracked Good Cracked Good 291 25 10 Cracked Good Cracked Cracked Cracked Cracked 292 20 15 Cracked Cracked Cracked Cracked Cracked Cracked 293 15 20 Cracked Cracked Cracked Cracked Cracked Cracked 294 10 25 Cracked Cracked Cracked Cracked Cracked Cracked 295 5 30 Cracked Good Cracked Good Cracked Good This series acts very similarly to Series 41. SERIES 42. (On Leather Hard) No Cone 5 Cone 7 Cone 9 290 Good Good Good 291 Good Good Good 292 Good Good Good 293 Good Good Good 294 Good Good Good 295 Good Good Good ON THE MANUFACTURE OF ENAMEL BRICK. 29 All slips are good both glazed and unglazed, except that the glaze flakes from the slip slightly. Slips, how- ever, fit perfectly. All slips are opaque at Cone 9. SERIES 43. (On Biscuit) Constant: N. C. Kaolin, 65; English Ball, 10; Carbonate of Soda, 1. Cone 5 Cone 7 Cone 9 Flint Spar Unglazed | Glazed Unglazed | Glazed Unglazed | Glazed 296 20 5 Cracked Cracked Cracked Cracked Cracked Cracked 297 15 10 Cracked Cracked Cracked Good Cracked Cracked 29S 10 15 Cracked Cracked Cracked Cracked Cracked Cracked 299 5 20 Cracked Cracked Cracked Cracked Cracked Cracked 30 f ) 25 Cracked Cracked Cracked Cracked Cracked Cracked Cracking is very bad. Slips also flake some but not badly. All slips are opaque at Cone 9. SERIES 43. (On Leather Hard) No. Cone 5 Cone 7 Cone 8 296 Good Good Good 297 Good Good Good 298 Good Good Good 299 Good Good Good 300 Good Good Good All slips work perfectly both glazed and unglazed. Glaze, however, flaked from slips; otherwise all trials were sound. 30 ON THE MANUFACTURE OP ENAMEL BRICK. TRANS. AM. CER.SOC. VOL.XII. Groc//iJT. MC Kaolin * 15-65 Brandy wine6par~ 5-55 Onto 8/tr. Hint - 0-60 Constants Not flotted$) Encf. Ball(riKejNozo)*/0, Carbonate <5oda~ I, STULL A = Good On Biscuit K= C^ajeat " C = CracKed » >> U^Gooct On Lea.t/zer>/iczT>ct •S s o 20 15 Flaked Flaked Good 336 Opq © 15 20 Flaked Good Good 337 glish glish rbona 10 25 Flaked Flaked Flaked 338 5 30 Flaked Flaked Good This series appears very similar to Series 47 opaque at Cone 8. All are SERIES 49. (On Leather Hard) Flaking in this series has increased over Series 48. All are opaque at Cone 9. 36 ON THE MANUFACTURE OP ENAMEL BRICK. TRANS. AM. CER. SOC. VOLXII. Group M. M. O.B. Encf. China Clay =/5to65 Brandym'neFelcLs/i. -5to55, ' Ohio 8 Hr. Flint - ot> 60 Constants Not Ftotted $>. E71(].BaU(Pif(e6No.20)*10 Carbonate 6oda * A. Clay 3D STULL ■$ A - Good On Biscuit K ■* Crazed » » □ - GoocfOn Leather Hard C = CracKed Os A 0* F = HaKed On Leather p FlaKed On Leather /iard ^ crs- Conclusions on Group V. Grazing and Cracking: The observations on crazing nnd cracking in Group V are the same as those of Group IV. Flaking: Flaking on leather hard hotly during burn- ing increases with increase in clay. Reducing clay and increasing flint or Cornwall stone, or both, reduces flaking during burning. The opposite is true of flaking in dip- ping. Comparing Groups A and IV shows a decrease in number of good slips on biscuit body by substituting Pikes Xo. 20 English ball clay for Tennessee No. 1 ball clay. Cracking and crazing hare increased. (See comparison of Groups I and II.) In comparing Groups V and II it is shown that the 48 ON THE MANUFACTURE OP ENAMEL BRICK. substitution of Cornwall stone for feldspar has increased crazing and flaking. Cracking remains practically the same. The fields of good slips on biscuit and leather hard bodies are smaller. A few good slips on bone dry body appear in Group V which are lacking in Group II. The limits of composition of good slips found in Group V are : On Biscuit On Bone Dry On Leather Hard North Carolina Kaolin English Cornwall Stone. . . Ohio Flint Carbonate of Soda Pikes No. 20 English Ball. 15 to 25 15 to 55 15 to 50 10 1 15 to 25 25 to 45 to 40 10 1 25 55 to 65 5 to 25 to 30 10 Constant Group VI. Series 63 to 68. SERIES 63. (On Biscuit) Constant English China , 15; English Ball No 20, 10; Carbonate of Soda, 1. Flint En? C. Stone Cone 3 Cone 6 Cone 8 Unglazed I Glazed Unglazed I Glazed Unglazed Glazed 436 60 15 Crazed Crazed Crazed Crazed Crazed Crazed 437 55 20 Good Crazed Good Crazed Good Crazed 438 50 25 Crazed Crazed Good Crazed Good Good 439 45 30 Good Crazed Good Crazed Good Good 440 40 35 Crazed Crazed Good Good Good Good 441 35 40 Good Crazed Good Good Good Good 442 30 45 Good Crazed Good Good Good Good 443 25 50 Good Crazed Good Good Good Good 444 20 55 Good Good Good Good Good Good Slips high in flint craze. Glaze tends to prevent craz- ing of slips. Crazing decreases with decrease in flint, in- crease in Cornwall stone and increase in temperature. All slips are opaque at Cone 3. Slips 43S to 444 are vitrified at Cone 9. ON THE MANUFACTURE OF ENAMEL BRICK. 49 SERIES 63. (On Bone Dry) No. Cone 3 Cone 6 Con< s Unglazed 1 Glazed Unglazed Glazed Unglazed Glazed 436 Crazed Crazed Crazed Crazed Crazed Crazed 437 Crazed Crazed Crazed Crazed Crazed Good 438 Good Crazed Good Good Good Good 439 Good Crazed Good Crazed Good Good 440 Good Crazed Good Crazed Good Good 441 Good Crazed Good Good Good Good 442 Good Crazed Good Good Good Cracked 443 Good Good Cracked Cracked Cracked 444 Good Good Good Good Crazed Good Crazing of slips practically the same as that observed in the same series on biscuit. Slips fit body very good, though not perfectly. SERIES 64. (On Biscuit) Constant: English China, 25; English Ball No. 20, 10; Carbonate of Soda, 1. Ene. Coie 3 Cone 6 Cone 8 \o. Flint c. Stone Unglazed I Glazed Unglazed Glazed Unglazed Glazed 445 50 15 Good Crazed Good Crazed Good Crazed 446 45 20 Good Crazed Good Crazed Good Crazed 447 40 25 Good Crazed Good Crazed Good Good 448 35 30 Good Good Good Good Good Good 449 30 35 Good Good Good Good Good Good 450 25 40 Good Good Good Good Good Good 451 20 45 Good Good Good Good Good Good 452 15 50 Good Good Good Good Good Good Slips fit body perfectly aside from crazing. Crazing decreases with decrease in flint* and increase in Cornwall stone. All are opaque at Cone 2. Slips 448 to 452 are vitrified at Cone 6. Slips 446 to 452 are vitrified at Cone 7. 50 OX THE MANUFACTUBE OF ENAMEL BRICK, SERIES 64. (On Bone Dry) Cone 2 Cone 6 Cone 7 Unglazed Glazed Unglazed Glazed i Unglazed Glazed 445 Good Crazed Good Crazed Cracked Crazed 446 Cracked Cracked Cracked Crazed Cracked Crazed 447 Cracked Crazed Cracked Crazed Cracked Good 448 Cracked Crazed Cracked Good Cracked Cracked 449 Crazed Crazed Cracked Cracked Cracked Cracked 450 Cracked Cracked Cracked Cracked Cracked Cracked 451 Cracked Good Good Good Good Good 452 Good Cracked Cracked Good Cracked Good The cracking, which is of- the so-called "crowsfoot" type, is not bad. Variation in composition and tempera- ture do not seem to influence the degree of cracking. No. 451 is very good at Cones 6 and 7. SERIES 64. (On Leather Hard) No. Cone 2 Cone 6 Cone 7 Unglazed , Glazed Unglazed | Glazed Unglazed 1 Glazed 445 446 447 448 449 450 451 452 Flaked Good Good Good Good Good Good Good Flaked Flaked Good Good Good Good Good Good Flaked Good Good Good Good Good Good Good Flaked j Flaked Flaked ! Good Good Good Good Good Good Flaked Flaked Good Good Good Good Good Flaked Flaked Flaked Flaked Flaked Flaked Good Good Flaking appears to decrease with decrease of flint and increase in Cornwall stone. Glaze tends to reduce the degree of flaking, but not to overcome it. A subsequent examination of duplicate .trials showed that slips were imperfectly bonded before burning since slips could be flaked off in small patches by pressing with the thumb nail. ON THE MANUFACTURE OF ENAMEL BRICK. SERIES 65. (On Leather Hard) 51 Constant: English China, 35; English Ball No. 20, 10; Carbonate of Soda, 1. No. Flint En e- 1 Cone 4 Cone 6 Cone 7 Stone 1 I'.iglazed I Glazed Unglazed | Glazed Unglazed 1 Glazed 453 45 10 454 40 15 455 35 20 456 30 25 457 25 30 458 20 35 459 15 40 460 10 45 Good Good Good Good Good Good Good Good Good Flaked Flaked Good Good Good Good Good Good Flaked Good Good Good Good Good Good Flaked Flaked Flaked Good Good Good Good Good Good Good Good Good Good Good Good Good Flaked Good Flaked Good Good Good Good Good Flaking is less than in Series 64. Flaking decreases with decrease in flint and increase in Cornwall stone. Slips 456 to 466 are good hard slips at Cone 7. No. 460 is a dense white porcelain. SERIES 66. (On Leather Hard) Constant: English China, 45; English Ball No. 20, 10; Carbonate of Soda, 1. No. Flint Eng. c. Stone Cone 2 Cone 6 Cone 7 Unglazed | Glazed Unglazed 1 Glazed Unglazed 1 Glazed 461 40 5 Good Good Good Good Good Good 462 35 10 Good Good Good Good Good Good 463 30 15 Good Flaked Flaked Flaked Good Flaked 464 25 20 Good Good Good Good Good Good 465 20 25 Good Good Good Good Good Good 466 15 30 Good Good Good Good Good Good 467 10 35 Good Good Good Good Good Good Slips fit body very well. Slip No. 463 is the only one that showed any signs of flaking. Glaze has a tendency to flake on the slips. Slips 464 to 467 are excellent as to fit, color and hardness. 52 ON THE MANUFACTURE OF ENAMEL BRICK. SERIES 67. (On Leather Hard) Constant: English China, 55; English Ball No. 20, 10; Carbonate of Soda, 1. No Flint Ene. c. Stone Cone 4 Cone 6 Cone 7 Unelazed I Glazed Unglazed | Glazed Unglazed | Glazed 468 30 5 469 25 10 470 20 15 471 15 20 472 10 25 473 5 30 Good Good Good Good Good Good Good Good Good Good Good Good Good Good Good Good Good Good Good Good Good Good Good Good Good Good Good Good Good Good Good Good Good Good Good Good All slips fit body perfectly. No cracking- r flaking could be detected. This is the best series in the group. Slips 470 to 473 are especially good at Cones 6 and 7. SERIES 68. (On Leather Hard) Constant: English China, 65; E nglish Ball , 10; Carbonate of Soda, 1. Eng. Cone 4 Cone 7 No. Flint C. Stone Unglazed Glazed Unglazed Glazed Unglazed | Glazed 474 20 5 Good Good Flaked Flaked Flaked Flaked 475 15 lu Good Flaked Flaked Flaked Flaked Flaked 476 10 15 Good Good Good Good Good Good 477 5 20 Good Good Good Good Good Good 478 25 Good Good Good Good Good Good Slips high in clay and flint have a tendency to flake. Decrease of flint and increase of Cornwall stone has re- Slips 477 and 478 are very good. duced flaking. ON THE MANUFACTURE OF ENAMEL BRICK. 53 TRANS. AM CER. SOC. VOL. XII 6 roup W. M. G. ft. Eng. China~/5to 65 Eng. C. Stone * Sto55 0/iio8Hr.riint ~0to60, Con jfants A'ot Piotted $L Eng. BaU(fi/d K - Crazed. On Btecui't O Good On Bo?ieff?y 0} A? F FiaXed On Leat/te/Wa rd r J Conclusions on Group VI. Crazing : Practically the same conclusions on crazing of the slip apply in this group as those observed in Groups IV and V. Cracking: Very little cracking occurred in slips ap- plied to bone dry body. Xo cracking occurred in slips applied to biscuit and leather hard bodies. Flaking: Slips both low and high in clay showed a tendency to flake. Evidently slips low in clay were im- perfectly bonded before burning. Flaking decreases with decrease in flint and increase in Cornwall stone. A comparison of Groups VI and V shows that the substitution of M. G. E. English China clay for North Carolina kaolin has decreased crazing, cracking and flak- ing. The fields of good slips on biscuit body are practi- 54 ON THE MANUFACTURE OF ENAMEL BRICK. cally the same size. A larger number of good slips appear on bone dry body, and the field of good slips on leather hard body has expanded to a comparatively large area. The slips are also superior in whiteness and vitrify at lower temperatures. A comparison of Groups VI and ITT shows that the substitution of English Cornwall stone for feldspar has decreased crazing, cracking and flaking. The fields of good slips on biscuit and leather hard bodies have in- creased and good slips on bone dry were obtained, which are absent in Series III. The limits of composition of good slips found in Group VI are : Or Biscuit On Lcathe Hard On Bone Dry M. G. R. English China Clay. 15 to 25 25 to 65 15 to 25 English Cornwall Stone 25 to 55 to 50 25 to 55 Ohio Flint . 15 to 50 to 45 20 to 50 Pikes No. 20 Eng. Ball Clay. 10 10 10 Carbonate of 1 1 1 GENERAL DEDUCTIONS. From previous practical experience in the manufac- ture of enamel brick and from the foregoing investiga- tions, the following rules are given for overcoming defects in enamel brick slips : ON THE MANUFACTURE OF ENAMEL BRICK. 55 Defects Arising in the Application of the Slips and Remedies for the Same. Principal Defects 1. Using freshly made slips. 1. Age slips a week or Pinholes more. 2. Dust on the surface of brick. 2. Remove all dust or scrub the surfaces to be dip- ped. 3 Pinholes in the surface of the brick. 3. Scrub surfaces to be dipped. 4. Bad dipping. 4. 5. (See Fig. 1, p. 717.) 5. Too high content of clay Reduce clay and increase in slip. the non-plastic portion, or add a soluble mater- ial as carbonate of soda, borax or silicate of soda. Cracking 6. Slips too high in China clay or kaolin. 6. Decrease China clay or kaolin and increase ball clay, or add a soluble material. 7. Allowing leather hard body to get too dry be- 7. Dip brick in a softer condition. fore dipping. 8. Do not apply slip over 8. Applying slip too thick. J r > of an inch thick. 9. Too fine grinding of slip. 9. Blunge slips instead of grinding. Flakim 10. Using slips too low in 10. clay. 11. Slips too high in China 11. clay or kaolin. 12. Oil or dust on dipping 12. surface. 13. In dipping on leather 13. hard ; dipping before brick have hardened suf- ficiently. increase clay and de- crease non-plastic por- tion. Decrease China clay or kaolin and increase ball clay. Scrub surfaces to be dipped. Allow brick to reach a firm leather hard condi- tion before dipping. 56 ON THE MANUFACTURE OF ENAMEL BRICKS. Slip Defects Arising in Burning and Remedies for the Same. Principal Defects 14. Slips too high in flint. 14. Reduce flint and in- crease clay, feldspar or Cornwall stone. 15. Slips too high in feld- spar or Cornwall stone. 15. Reduce feldspar or Corn wall stone and increase clay. Crazing 16. With feldspar as a flux; burning slips at too high a temperature. 16. Reduce burning temper- ature. 17. With Cornwall stone as a flux; burning slips at 17. Increase burning tem- perature. 18. too low a temperature. Too high content of clay 18. Reduce clay and in- in slips. crease flint, Cornwall stone or feldspar. Cracking 19. Too high content of feld- spar or Cornwall stone in slips. 19. Reduce feldspar or Corn- wall stone and increase flint. 20. Dipping slips too thick. 20. Same as No. 8. 21. Too high content of clay in slips. 21. Reduce clay and in- crease Cornwall stone, flint or feldspar. 22. Too high content of feld- spar in slips. 22. Reduce feldspar and in- crease Cornwall stone. Flaking 23. Too high content of flint in slips. 23. Reduce flint and in- crease Cornwall stone. 24. Burning slips at too high 24. Reduce burning temper- a temperature. ature. SLIPS TESTED AS ENGOBES FOR STONEWARE. The problem of producing a slip or engobe to be used as a white lining for stoneware was confronted. Slips No. 292, 298, 464 and 470 were selected as the starting point. These slips were applied to three different stoneware clays, viz. : Whitehall clay from Whitehall, 111., having a com- paratively high shrinkage: Macomb clay of medium shrinkage from Macomb, 111. ; Bloomingdale clay having a comparatively low shrinkage from Bloomingdale, Ind. Trials were made in the form of cups, jiggered in one piece. Cnps were taken from the molds, finished leather ON THE MANUFACTURE OF KXA1IEL BRICK. 57 hard, and slips applied to the inside in two coats. Over this a clear glaze was applied in one coat. The slip and glaze were scraped off at the outside rim. A brown glaze was applied to the outside by sinking the cup down into (Stoneivar'e Cc//r W(t/? lV/}ite£/;$obe A 'net CLeay* Glaze /n^side /) 'nd Brown 6/aze Oot^s ide. the glaze until the brown glaze touched the white slip and glaze extending over the rim. The cups were dried and burned at Tone 3. All four slips worked perfectly on all three stoneware bodies. DISCUSSION. Mr. Ramsay. There is a lot I would like to say on this subject, as it is an interesting one, but the trouble we have in the enamel brick business is not with the slips but in the cost of manufacture and results out of kilns. I know Mr. Stall has put a good deal of time and work on his paper, and I agree with him on many of his results. To ^et a slip as near to the clays as possible you have to use lime, and when that is added it changes the results entirely. He made the claim that the slip will peal off with the dry clay. I would like to take exception to the 58 ON THE MANUFACTURE OP ENAMEL BRICK. remark for the reason that ball clay will not come off. With China clay it will come off, but by a mixture of both it will not come off. Mr. Stall : I do not think Mr. Kamsay's statement is antagonistic to what has been brought out in my paper. If a slip is high enough in ball clay it will cling to the body. Enamel brick makers as well as potters are limited in the amount of ball clay they can use on account of the bad color it imparts. For this reason 1 used ten per cent ball clay as the high limit in all slips. It is quite essential to have some ball clay in the slip, but as a rule the less ball clay present the better color you get. My experience shows that a slip made from ball chvy will stick very well but will crack badly. Ball clay possesses better adhesive qualities than China clay or kao- lin, and seems to adjust itself better to the body both in drying and burning. Mr. Ashley: I think to slightly increase the China clay slip by adding a small quantity of silicate of soda, will give some of the general characteristics of ball clay. Mr. Ramsay: It may be in certain respects. If yon add a certain percentage of silicate of soda you destroy the working qualities as regards the dipping. I suppose the idea is to decrease the water content and that only affects the drying shrinkage. There is no effect afterwards, of course, and I think the difference is so slight that it is hardly worth trying. Mr. Stull : My experience in using silicate of soda was that it caused the slip to settle very rapidly and cake hard at the bottom. It requires constant agitation to keep the slip in suspension. Perhaps I was using too high a percentage, although it was only % of one per cent, how- ever. Mr. Ashley-. I would suggest that even 1/10 of one per cent of silicate of soda acts very vigorously on clay, and we should experiment with 1/100 of one per cent rather than 1/10. OX THE MANUFACTURE OP ENAMEL BRICK. 59 Mr. Worcester: I would like to ask Mr. Stull if he lias studied the hardness of these slips with the various contents of spar. In some work we have been doing at Ohio State that was one of the requirements to produce a hard or nearly steel hard slip and I, of course, am very much interested, and was wondering if Mr. Stull had ob- served this point in particular or at all. Mr. Stull : When each slip was shaken up and turned out of the can before dipping, a little of it was cast into trials, 1%" long, y 2 " wide and 14" thick. These were placed in the sagger and burned with the dipped trials and used to determine the porosity. It was desirable to know what was the limit of porosity for these slips which would withstand the freezing test. That part of the work is under way at the present time. Mr. Stover: I would like to ask what percentage of absorption you got, or was it around 1%? You spoke of making trials for absorption for your slips and that would follow in your paper. I happen to be looking along that iine just now and would like to know. Mr. Stull: There are two methods of determining the porous nature of brick. One is the percentage of absorp- tion and one is the percentage of porosity. The absorption, as Ave know, is usually determined by weighing the brick dry then soaking it 48 hours and weighing it again. By observing the increase in weight and dividing that increase by the weight of the brick gives what is called percentage absorption. The percentage porosity is approximately 2^0 times percentage absorption. The porosity of these slips was determined by Prof. Purdy's formula. The porosities of the slips have varied according to the kind and amount of flux and the temperature of burning. Perfect fitting slips Avere obtained from as soft as chalk up to a hard vitrified and glossed condition. Mr. Stover: And do you not remember in figures what the result was? Mr. Stull : Xo, I do not. P ;> ^ V !*?•/ 7 «X< **0*V^V 3$ 3r ,<. i*'«l 1,-1 » r WW \K > & X i**1& ,-Vw: UNIVERSITY OF ILLINOIS-URBANA L 3_01 12 052567101 A * #L1* v ■ % 0- v gr A** V.