J^ir^tfjr 4 • O.t V ■>*.■*■# ;<*$^i W^z ^^^SV^ :*K kgm \m ^ . & UNIVERSITY OF ILLINOIS LIBRARY Class Book its. Volume *-ir. . V ■,*> •\>r. The person charging this material is re- sponsible for its return to the library from which it was withdrawn on or before the Latest Date stamped below.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. UNIVERSHY OF ULINOIS LI BRARY AT URBANA-CHAMPAIGN / University of Illinois Bulletin Vol. VI. JULY 14. 1909 No. 39 [Entered February 14, 1902, at Urbana, Illinois, as second-class matter under Act of Congress of July 16, 1894.] BULLETIN No. 11 DEPARTMENT OF CERAMICS C. W. ROLFE. D,r«tor A Cheap Enamel for Stoneware PART II. By RAY THOMAS STULL 1908—1909 published fortnightly by the university A CHEAP ENAMEL FOR STONEWARE. Part II. R. T. Stull, Urbana, Illinois. The last contribution of "A Cheap Enamel for Stone- ware," in Vol. X, was sent in for publication three days after the last trials came from the kiln. The most promis- ing enamels of the work done up to that time were the members of Series IX, and the best one of the series was No. 35. As has been noted, no craze marks were observed on Xo. 35, when taken from the kiln. After three weeks' time a craze mark appeared on the bottom of one trial. Crazing has been going on gradually until now the trials are completely checkered with craze marks. The author is of the opinion that the crazing is due to the softness of the body rather than to the glaze itself, since the trials were burned at cone 01. series x. The maturing temperature of Xo. 35 is altogether too low for the stoneware body and too high for other .types of ware, notably those maturing at cone 04. Hence it was thought advisable to construct a series starting with a glaze of the same type as Xo. 35, but which should be more fusible. The RO, A1 2 3 and P 2 ,, which are the same as those in Xo. 35, are kept constant throughout the series, the two variable members being Si0 2 and B 2 3 . Each succeeding member has the B 2 3 decreased one tenth and the SiQ 2 increased accordingly. Two fritts were A CHEAP ENAMEL FOR STONEWARE. made for Series X, which have the following formulae and batch weights : Fritt G. Formula Batch weights S571 CaO] f2.3 Si0 2 Bone Ash I- .357 Al 2 Osi Zinc Oxide 1429 ZnOj L -2857P 2 05 N. C. Kaolin Flint 30.75 4.03 32.09 33.13 Fritt H. Formula Batch weights .25 K 2 0] f2.125 SiO= J- .5625 AlsOs-l .250 P2O5 .75 CaO J [1.250 B.Os Feldspar Bone Ash N. C. Kaolin Boracic Acid 30. SO 17.09 17.83 34.28 Fritt G was calcined in a Hinted sagger at cone 8. Fritt H was fused in a Hinted crucible and quenched in water. Both fritts were ground dry to a fine powder ready for weighing. Glazes. Formulae Batch weights V S3 -• 2 u 6 < 6 d PQ CuUh O '/ O u N - '5c. ~ u. — 1/ cd - 36 | . .6 1 .2 .55 2.3 .2 | 1.0 81.90 4.45 7.07 6.58 37 ! • 2.4 " |' .9 3.06 5.28 73.91 4.24 7.09 6.42 38 I ' 2.5 " 1 .8 6.14 10.60 65. S8 4.02 7.11 6.25 39 | ' " 2.6 .7 9.24|l5.94 57.80 3.81 7.13 6.08 40 | ' " 2.7 " 1 .6 12.35l23.31 49.68 3.59 7.15 5.92 41 I ' " " 2.S " .5 15.48l26.71 41.51 3.38 7.17 5 . 7 5 42 I ' " a " 2.9 .4 18.63|32.14 33.30 3.16 7.19 5.58 43 1 ' " " 3.0 .3 21.79137.60 25.04 2.94 7.21 5.42 44 | ' " " 3.1 .2 24.79|43.09 16.74 2.72 7.23 5.25 45 1 ' ' " " " 3.2 .1 28.17|48.60 S.39 2.51 7.25 5.0S 46 | ' " ! " " 1 3.3 " .0 31.39l54.16 2.28 7.27 4.90 A CHEAP ENAMEL FOR STONEWARE. 5 These glazes were applied to bone dry stoneware crocks but flaked so badly on drying that the series was abandoned. A few subsequent dips of the two extremes of this series (Nos. 36 and 4G ) worked very satisfactorily on biscuit. No further investigation was made into the working qualities of the members of this series on biscuit since the work is mainly along the line of single fire enamels. SERIES XI. Series X was modified in series XI to overcome flak- ing. In this series the same formulae are used as in scries X, the difference being that in series XI the raw clay is increased from 0.1 to 0.15 and Tennessee ball clay No. •"> is used in place of Georgia kaolin. This required the making of two new frit ts (I and J), since the excess clay above r the other cracks in drying before it goes into the kiln, and when the glaze begins to fuse it beads and crawls; and in the other case we get an effect which does not appear before it goes into the kiln. I think manufacturers, as a rule, for the first kind of beading, use a material something like calcium sulphate, and some use glue to hold the glaze together in drying, making it tougher. For the second kind, the kind happening in the kiln and which does not show up in the drying, boracic acid is used; or, in a terra cotta glaze the ZnO is reduced with MgO. The latter fault is due to im- perfect glaze, while the former can be overcome mechanic- ally, i. e. by applying the underslip or glaze thinner. Mr. Fackt : May I ask Mr. Stephani whether he has used Cornwall stone in place of the feldspar to prevent the crawling and cracking which he speaks of as happen- ing before the ware goes into the kiln? 14 A CHEAP EXAMEL FOR STOXEWARE. Mr. Stephani: I never used Cornwall stone in any glaze; but I find the best way to overcome that effect is by remedying the underslip, or putting less of it on the ware. Mr. Miller: Mr. Stull tells us he finds an improve- ment in color by substituting magnesium for tin. Mr. Purely: The substitution of magnesium for what? Mr. Stull: An improvement in color by substituting magnesium oxide for zinc oxide. It does make a little difference in the fusibility. Glazes containing MgO are not quite so fusible as glazes containing ZnO, other things being equal. Dr. Sinionis, in his work on cones, in which he used magnesium oxide, points out that the action of the MgO in the cones is to hold the cones up to a certain point when the fusion is comparatively sudden. It is claimed for that reason that they are better indicators of temperature than the regular Seger cones. We are getting more light all the time as to the action of MgO in ceramic mixtures. In fact, we do not yet know all of its possibilities. The magnesite which I used was rather a pure variety obtained from the Foote Mineral Company. I am told that a good variety of the Grecian magnesite is delivered in New York for about twenty-four dollars a ton. If it can be used successfully it will cheapen enamels wonderfully and fill a long felt want for the lower grades of ware. Mr. Frink : One thing has occurred to me in regard to this discussion of magnesia. Magnesia is used in glass to some extent, usually being found as an impurity in the lime, and experiments have been made which show that the viscosity is very much reduced thereby. Mr. Purely: The viscosity is reduced? Mr. Frink: Yes. That bears out what the gentle- man has said. When the temperature rises to a certain point, liquefaction is reached more rapidly. Does not the similar action of borax account for the beneficial results of this material in the case of crawling or beading, be- cause of the filling of the interstices with liquid? A CHEAP ENAMEL FOR STONEWARE. 15 Mr. Purdy. Was it used in a small pot or a big batch? Mr. Frink: I have experimented with it in tank of capacity of 600 tons, and also with quantities of fifty or sixty pounds. Mr. Purdy: The viscosity seemed to be the same in both instances? Mr. Frink : Yes. Mr. Purdy: What was the effect of magnesia on de- vitrification? Mr. Frink: That seems to vary according to con- ditions, under which it is melted. If melted under a high reducing flame devitrification takes place slowly; but under a high oxidizing flame it takes place rapidly. Mr. Purdy: Is that peculiar of your magnesium glasses or is it true also of lime glasses? Mr. Frink: Yes; it is also true as to lime glasses; but with the magnesium glasses it is particularly so and I attribute it to the more liquid condition. That is my theory. Mr. Purdy: We have to have equivalent of devitri- fication to have opacity. Mr. Frink : Yes; and I imagine if you put that under oxidizing conditions you will get that more rapidly. Mr. Purdy: I will ask Mr. Stull if magnesium in the form of light, fluffy oxide has the same effect as when in- troduced as magnesite? Mr. Stull: I have never used the light commercial magnesia only in a fritt on one or two occasions, and have never made any comparisons between it and the mineral magnesite. Commercial magnesia is comparatively ex- pensive. We can obtain magnesite which will analyze very high in MgC0 3 , with very little impurity which would cause discoloration. There is a deposit in California which is claimed by some to be better than the Grecian, but the cost of mining it and shipping it east is greater. By a little sorting, a comparatively pure grade can be had as low as thirty to fortv dollars a ton. 16 A CHEAP ENAMEL FOB STONEWARE. Mr. Purdy: I asked that question in the interest of Hottinger, Barringer, and Hull. Mr. Stall: What is the effect of magnesia upon iron color in glass? In series twelve and thirteen Tennessee ball clay was used, yet the glazes do not show any trace of cream color. Mr. Frink : It is so contradictory in action that I cannot answer the question definitely. We sometimes get one effect and sometimes another. I think this is a mat- ter of oxidizing and reducing conditions. It seems to me you would get better results if steam were thrown into the kiln. It seems you have a condition analagous with that prevailing in a lime kiln. I made some experiments one time, introducing steam into a lime furnace. It was found that devitrification was very much enhanced. There are two forms of devitrification, one due to pressure and the other to oxidation. Pure oxygen will produce de- vitrification. Mr. Purdy. I note that Mr. Stull did not draw any conclusions in regard to soda or potash feldspar, as fluxes in these glazes. Mr. Stull: As yet no experiments have been made in this line to determine that. This will probably be in- vestigated later. *&< N *&: ^^'^ y^wC:JA J , ^*. %m *EsE