Underglaze is a method of painting pottery in which painted decoration is applied to the surface before it is covered with a transparent ceramic glaze and fired in a kiln. Because the glaze subsequently covers it, such pottery paint is completely durable, and it also allows the production with a surface that has a uniform sheen. Pottery Underglaze decoration uses pigments derived from oxides which fuse with the glaze when the piece is fired in a kiln. It is also a cheaper method, as only a single firing is needed, whereas overglaze decoration requires a second firing at a lower temperature at the pottery house. Their quality makes them suitable for use with a number of decorating techniques including airbrushing, antiquing and brushstrokes. One stroke is all you need for most design work. One or two additional strokes may be added for depth and shading while the color is still wet. if additional coats are applied after the color has dried, the painted pottery may cause popping off, bleeding and bubbling.
How to paint bisque pottery? The underglaze porcelain paints can be applied directly to bisque. They may be applied over most and underglazes, including Cover-Coats and another underglaze blue porcelain, allowing the base color to show through. They may also be used to change clay slip, most glazes, fired snow, and other colors. There's an unlimited way for pottery painting, so why you don't test?
More about Painting and Glazing can be found in the article Underglazes on Wikipedia