The basis of all enamels is a highly transparent and fusible glass, called frit, flux, or paste, which readily receives a color on the addition of the metallic oxides.

Preparation

Red lead, 16 parts; calcined borax, 3 Parts; pounded flint glass, 12 parts; flints, 4 parts. Fuse in a Hessian crucible for 12 hours, then pour it out into water, and reduce it to powder in a biscuit-ware mortar. The following directions will serve to show how the coloring preparations are made: Black enamels are made with peroxide of manganese, or protoxide of iron, to which more depth of color is given with a little cobalt. Violet enamel of a very fine hue is made from peroxyde of manganese in small quantity with saline or alkaline fluxes. Red enamel is made from protoxide of copper. Boil a solution of equal parts of sugar and acetate of copper in four parts of water. The sugar takes possession of a portion of the cupreous oxide, and reduces it to the protoxide: when it may be precipitated in the form of a granular powder of a brilliant red. Alter about two hours of moderate boiling, the liquid is set aside to settle, decanted off the precipitate, which is washed and dried. By this pure oxide any tint may bo obtained from red to orange by adding a greater or smaller quantity of peroxide of iron. The oxide and purple of cassius are likewise employed to colored enamel. This composition resists a strong fire very well. GREEN enamel can be produced by a mixture of yellow and blue, but is generally obtained direct from the oxide of copper, or better still with the oxide of chrome, which last will resist a strong heat.

Yellow

Take one part of white oxide of antimony, with from one to three parts of white lead, one of alum, and one of sal ammoniac. Each of these substances is to be pulverized, then all are to be exactly mixed, and exposed to a heat adequate to decompose the sal ammoniac. This oj>eration is judged to be finished when the yellow color is well brought out.

Blue

This color is obtained from the oxide of cobalt, or some of its combinations, and it produces it with such intensity that only a very little can be used lest the shade should pass into black. A White enamel may be prepared with a calcine formed of 2 parts of tin and 1 of lead, calcined together: of this combined oxide, 1 part is melted with two parts of fine crystal and a very little manganese, all previously ground together. When the fusion is complete, the vitreous matter is to be poured into clear water, and the frit is then dried and melted anew. Repeat the pouring into water three or four times, to insure a perfect combination. Screen the crucible from smoke and flame. The smallest portions of oxide of iron or copper admitted into this enamel will destroy its value.

The artist prepares his enamel colors by pounding them in an agate mortar, with an agate pestle, and grinding them on an agate slab, with oil of lavender rendered viscid by exposure to the sun, in a shallow vessel, loosely covered with gauze or glass. He should have alongside of him a stove, in which a moderate fire is kept up, for drying his work whenever the figures are finished. It is then passed through the muffle.