Glaze is actually composed of ingredients which will melt and become a thin layer of glass on the clay when the piece is placed in a kiln and fired to a high temperature. Glazes are colored by the presence of mineral oxides and carbonates. There are many factors which affect the color of the glaze. The ingredients may react to produce variations. The texture of the surface may catch more glaze arid cause an interesting pattern of color. The intensity of the heat may produce a wide range of color.
There are transparent glazes. These are usually glossy and may or may not be colored. The enamel glazes are opaque and usually applied heavier than the transparent glazes. A mat glaze is dull and usually opaque. For most purposes, little else need be known about glazes. It is a study involving chemistry and art, but the average person can have a reasonable amount of success without making a complete study of glazes.
To mix a glaze, it is necessary to have a scale which measures gram weights; a fine brass wire screen, 60 or 80 meshes to a square inch; and a pan in which to mix the glaze.
Balance the scales. Line the ingredients up in the order that they are listed in the recipe. Measure the ingredients carefully, checking the name with the recipe and the container label so that no mistakes are made. Dry-mix the powders. Add a little water at a time to make a smooth paste. Add more water until the glaze is a thick creamy consistency. Pass the glaze through a fine mesh screen. Add a tablespoonful of gum arabic which has been dissolved in cool water over night. Add water if necessary.
To increase the glaze batch, multiply each amount by a number which will yield a sufficient amount of glaze.
A medium-sized batch of milky transparent glaze which matures at a temperature of cone .07 or cone .06 (melting point measured with a Sczer cone) includes the following ingredients:
Lead Carbonate (White Lead)
After the piece has been "bisque-fired," the glaze is applied. Dip small pieces into an open-mouthed jar containing the thoroughly stirred ingredients. The pieces should be dipped several times until a coating of glaze has accumulated on the bowl to a thickness of about 1/16 inch. Fingermarks may be covered by painting those places with a soft water-color brush. The glaze should be scraped from the bottom of the piece so that it will not stick to the tripods in the firing.
Another method of applying glaze is to brush it on. An inexpensive soft flat paintbrush is used. The glaze should be stirred thoroughly. To glaze the inside, pour a cupful of glaze into the bowl or jar and turn the piece slowly until the entire surface is coated with glaze. Clean off any that has dripped down the sides. With a brush, pat the glaze on the outside walls of the bowl or jar and turn the piece slowly until the entire surface is coated with glaze. Clean off any that has dripped down the sides. Turn the piece around as the glaze is applied, doing one coat over the entire piece before applying a second and third coat. The patting technique is better than stroking the piece with the brush. The glaze will fuse more evenly.
If a paint spray is available, glaze may be diluted and placed in the spray gun and applied evenly to the pottery. This method is especially good when the piece has been decorated with underglaze colors.