General Info

CERAMIC COLORS

Color is an important characteristic of many ceramic products and when used properly it considerably enhances the aesthetic appearance. Ceramic colors are calcined blends of metal and ceramic oxides that have been reground into a fine powder. These stains consist of crystalline solids and their properties depend on the properties of the crystal lattices constituting them. Some metal oxides which are relatively inert and do not undergo significant changes during application and firing can be used as ceramic stains, however, produced ceramic stains have some superiorities. Admittedly, these stains produce much more homogeneous, consistent and repeatable colors than using raw oxide colors. Secondly, some metal oxides which are normally toxic in character can be safely used when prepared as ceramic colors. Unfortunately, most ceramic stains have crystal lattices that are unstable at high temperatures and readily affected by the presence of fluxing materials such as glazes, fluxes and vitrous bodies. Consequently, a stable crystal lattice may become unstable when heated to high temperatures. It is for this reason that most compounds and colors used in ceramic decoration are very susceptible to the conditions during firing. A successful and reproducable industrial color application can be obtained with a suitable combination of crystal lattice, heat treatment and stain environment. From this approach, if coloring oxides or stains are used in suitable glazes or applied to the ware with suitable fluxes then they will not react with their environment and change their crystal structure.
Application techniques of ceramic colors:
There are five ways in which ceramic colors can be applied to a glazable ceramic article: as a body stain, as an engobe, as an underglaze color, as a colored glaze and as an overglaze or glass color.
The use of body stain refers to a pigment added to the body formulation itself.
An engobe is a layer of colored clay body which is applied onto an unfired body in order to improve the decorative finish.
Underglaze decoration is the application of color to a bisque body before glazing.
In colored glazes, the stain is dispersed in the glaze itself.
Overglaze or glass colors are applied to the already formed and fired glaze as an overcoat and fired again.
The selection of technique depends on the requirements of the particular application.