Definition of a Stain: A stain is essentially an oxide or series of oxides and opacifiers which have been blended together, calcined (or fired), then ground to a 200 or so mesh powder. The reasons for using a stain versus an oxide, etc. are (1) Stability of Color — an important criteria for wall tiles, sanitary ware, etc. (2) Insolubility — an insoluble (in water) stain greatly diminishes the risk in handling wet glazes when dipping or pouring, etc. (3) Color — the fired color of most stains is identical to the raw color because it has already been fired. It is, therefore, easier to use or to mix to achieve another color. It can also be mixed with a variety of medium to turn them into china paints, enamels, silk screen colors, decals, etc.