Underglazes do not contain silica (that much anyway) and so, are not glassy. Usually a what you see is what you get in color. Can be treated similarly to paints. Are good for details and smaller areas. Can be applied to both green ware and bisque ware. Can be made shiny with a few coats of clear glaze in the glaze firing.
Intro...
Color mixing
Value (with water)
Value (tints & shades)