Part 111

Fire this very hard.

II.—Zinc 6 pounds Flint 4 pounds China clay 4 pounds Oxide of cobalt 5 ounces

Hard fire.

III.—Whiting 3 3⁠/⁠4 parts Flint 3 3⁠/⁠4 parts Oxide of cobalt 2 1⁠/⁠2 parts

Glost fire.

Turquoise Stain.—

Prepared cobalt 1 1⁠/⁠2 parts Oxide of zinc 6 parts China clay 6 parts Carbonate of soda. 1 part

Hard fire.

«MATERIALS:»

«Tin Ash.»—

Old lead 4 parts Grain tin 2 parts

Melt in an iron ladle, and pour out in water, then spread on a dish, and calcine in glost oven with plenty of air.

«Oxide of Tin.»—

Granulated tin 5 pounds Niter 1⁠/⁠2 pound

Put on saucers and fire in glost oven.

«Oxide of Chrome» is made by mixing powdered bichromate of potash with sulphur as follows:

Potash 6 parts Flowers of sulphur 1 part

Put in saggar, inside kiln, so that fumes are carried away, and place 4 or 5 pieces of red-hot iron on the top so as to ignite it. Leave about 12 hours, then pound very fine, and put in saggar again. Calcine in hard place of biscuit oven. Wash this until the water is quite clear, and dry for use.

«Production of Luster Colors on Porcelain and Glazed Pottery.»—The luster colors are readily decomposed by acids and atmospheric influences, because they do not contain, in consequence of the low baking temperature, enough silicic acid to form resistive compounds. In order to attain this, G. Alefeld has patented a process according to which such compounds are added to the luster preparations as leave behind after the burning an acid which transforms the luster preparation into more resisting {173} compounds. In this connection the admixture of such bodies has been found advantageous, as they form phosphides with the metallic oxides of the lusters after the burning. These phosphides are especially fitted for the production of saturated resisting compounds, not only on account of their insolubility in water, but also on account of their colorings. Similarly titanic, molybdic, tungstic, and vanadic compounds may be produced. The metallic phosphates produced by the burning give a luster coating which, as regards gloss, is not inferior to the non-saturated metallic oxides, while it materially excels them in power of resistance. Since the lusters to be applied are used dissolved in essential oils, it is necessary to make the admixture of phosphoric substance also in a form soluble in essential oils. For the production of this admixture the respective chlorides, preeminently phosphoric chloride, are suitable. They are mixed with oil of lavender in the ratio of 1 to 5, and the resulting reaction product is added to the commercial metallic oxide luster, singly or in conjunction with precious metal preparations (glossy gold, silver, platinum, etc.) in the approximate proportion of 5 to 1. Then proceed as usual. Instead of the chlorides, nitrates and acetates, as well as any readily destructible organic compounds, may also be employed, which are entered into fusing rosin or rosinous liquids.

«Metallic Luster on Pottery.»—According to a process patented in Germany, a mixture is prepared from various natural or artificial varieties of ocher, to which 25–50 per cent of finely powdered more or less metalliferous or sulphurous coal is added. The mass treated in this manner is brought together in saggars with finely divided organic substances, such as sawdust, shavings, wood-wool, cut straw, etc., and subjected to feeble red heat. After the heating the material is taken out. The glazings now exhibit that thin but stable metallic color which is governed by the substances used. Besides coal, salts and oxides of silver, cobalt, cadmium, chrome iron, nickel, manganese, copper, or zinc may be employed. The color-giving layer is removed by washing or brushing, while the desired color is burned in and remains. In this manner handsome shades can be produced.

«Metallic Glazes on Enamels.»—The formulas used by the Arabs and their Italian successors are partly disclosed in manuscripts in the British and South Kensington Museums; two are given below:

Arab Italian Copper sulphide 26.87 24.74 Silver sulphide 1.15 1.03 Mercury sulphide — 24.74 Red ocher 71.98 49.49

These were ground with vinegar and applied with the brush to the already baked enamel. A great variety of iridescent and metallic tones can be obtained by one or the other, or a mixture of the following formulas:

I II III IV V VI Copper carbonate 30 — — 28 — 95 Copper oxalate — — — — 5 — Copper sulphide — 20 — — — — Silver carbonate — 3 — 2 1 5 Bismuth subnitrate — 12 — — 10 — Stannous oxide — — 25 — — — Red ocher 70 85 55 70 84 —

Silver chloride and yellow ocher may be respectively substituted for silver carbonate and red ocher. The ingredients, ground with a little gum tragacanth and water, are applied with a brush to enamels melting about 1814° F., and are furnaced at 1202° F. in a reducing atmosphere. After cooling the ferruginous deposit is rubbed off, and the colors thus brought out.

Sulphur, free or combined, is not necessary, cinnabar has no action, ocher may be dispensed with, and any organic gummy matter may be used instead of vinegar, and broom is not needed in the furnace. The intensity and tone of the iridescence depend on the duration of the reduction, and the nature of the enamel. Enamels containing a coloring base—copper, iron, antimony, nickel—especially in presence of tin, give the best results.

«To Toughen China.»—To toughen china or glass place the new article in cold water, bring to boil gradually, boil for 4 hours, and leave standing in the water till cool. Glass or china toughened in this way will never crack with hot water.

«How to Tell Pottery and Porcelain.»—The following simple test will serve: Hold the piece up to the light, and if it can be seen through—that is, if it is translucent—it is porcelain. Pottery is opaque, and not so hard and white as porcelain. The main differences in the manufacture of stoneware, earthenware, and porcelain are due to the ingredients used, to the way they are mixed, and to the degree of heat to which they are {174} subjected in firing. Most of the old English wares found in this country are pottery or semichina, although the term china is commonly applied to them all.