Onglaze colors are applied on the surface of the fired glaze to which they adhare by fusion after being fired at a suitable temperature.
Onglaze colors can be applied in the following ways:
1- Direct screen printing
2- Transferring (decals)
3- Brush application
4- Spraying
5- Powdering

They can be used for the decoration of enameled and ceramic ware. The desirable properties in onglaze colors are that they should fuse in the kiln to form a glassy bond with the underlying glaze, they must not run and blur the design, they must be resistant to acids from foods and alkalies from detergents and they must have almost the same thermal expansion with the glaze.

Onglaze colors are being sold in powder form. Depending on the application method they should be mixed with a water based or oil based medium at the ratio
30-40 % ,stirred and pasted well until having a homogeneous creamy mixture.
The ratio of color to medium may not be the same in every color.
Powder colors should be kept dry. Color pastes should be kept in tightly covered containers and stirred well before use.

Correctly applied and fired color will have a smooth and glossy surface,no cracks and blisters appearing on the surface. You should avoid from too much thick application. If two or three coats will be applied one over the other, you should choose a finer screen and use less medium.

Recommended mesh sizes :
for multiple coat application 100-120 threads/cm
for one coat application 70-90 threads/cm

Recommended firing temperatures :
for enamel 780-800°C 3-4 minutes
for ceramic 850-900°C 20-30 minutes
In order to get a good result, the glaze under the decoration should have a higher melting temperature. If the glaze is dark in color, before applying the colors, covering white can be used as a base coat.

Almost all colors can be mixed with each other, however, expected shades can not be reached in every case. Cadmium containing red and orange colors can be mixed at every ratio with each other but restrictively with the others. These colors give good results only in fast firing cycles. Some colors, especially pink, are affected from the reducing gases in the kiln atmosphere so well ventilated kilns should be used.

All ceramic pigments and paints are due to crystal structures resulting from chemical reactions between some chemical compounds. They shouldn’t be inhaled or swallowed.