What is an Underglaze?

Pottery underglaze is a coloured, matte glaze applied to greenware [unfired clay] or bisque-fired pottery that is applied first [underneath] a clear top glaze. It acts like specialised paint, containing clay, colourants, and flux, allowing for detailed, non-running, and vibrant designs that remain exactly where they were painted before firing.

Underglazes are generally used for decorative work, providing artists with high control and the ability to create vivid, detailed ceramic pieces.

Key Characteristics and Uses:

• Application: Applied to leather-hard or bisque-fired pieces using brushes, sponges, or spraying.

• Stability: Unlike glazes, underglazes do not move or bleed

• Finish: They fire matte unless covered with a clear glaze.

• Colour Reliability: The colour is usually similar to the fired result.

• Versatility: Ideal for intricate designs, painting, sgraffito (scratching through), or mishima (inlay) techniques.

How they are used

Draw with a lead pencil the outline of your design on greenware to get a sense of the illustration you are going to paint. Once bisqued, the pencil burns off completely and leaves only the underglaze painting. It is recommended to test a few tiles to see if your particular pencil burns completely off, some coloured pencils endure firings so make sure your pencil is ok first before using underglazes.

Underglazes can also be diluted and used like a watercolour style, just don’t dilute them too much. They can also be mixed together to form new colours, however this can have unpredictable results so better to test this as well.

Another useful procedure tip is to paint light to dark. Start with the lightest colours and progress through your design using gradually darker colours until finishing in black [subject to your design of course].

And make sure the underglaze is completely dry before applying the clear glaze on top to avoid smudging.