August 1, 2003, Newsletter Issue #150: Underglazes: their uses

Tip of the Week

Underglazes as we know them, are opaque. They are formulated from colour pigment and clay to give solid, opaque coverage.

Remember that underglazes are to be used for wide area coverage. Underglazes are poor choices for design work. Since it is necessary to apply three coats for effective coverage, you can see how difficult it would be to make three lines directly on top of each other. Underglazes should be applied to dry greenware. If greenware is still damp when applied, the underglaze colours may chip off after firing.

It is best to thin down the first coat of underglaze with about two parts of colour to one of water. This is called a scrub coat. The second and third coats are applied at full strength. Remember that your colours must be dry before taking any next step, whether it is firing or adding design work over your underglaze base.

The clay and colour combination contained in underglazes form a bond with the greenware after being fired. Proper overglaze decorating begins with the greenware. Greenware which is to be overglazed should be carefully cleaned and fired to cone 04.

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