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What Are Underglazes?

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Underglazes are used in pottery to create designs and patterns that will come up through the glaze covering them, which can give the surface more visual depth and character. Although they are often used under clear glazes, they can also be used under other, generally light colored, transparent glazes. But, what are "underglazes"? There are different types, and they can be confusing.

Under the Glaze

"Underglaze" as a term can mean any decoration that is applied, almost always in a fluid form, on the pottery surface before any glaze is applied. In this blanket sense, underglazes can encompass slips, engobes, and stains, as well as products that are marketed as underglazes.

Commercial Underglazes

Painting done on low-fire pottery using commercial underglazes.
Photo © 2008 Beth E Peterson

Commercial underglazes used to be formulated to be basically highly pigmented colored slips: raw pigment, plus clay, plus water. Like all slips, they were made to be applied to the wet or leather-hard clay before it was bisqued.

Today, most underglazes on the market are formulated more like engobes. They are created using fritted material, which reduces shrinkage and allows them to be applied to bisqueware. (In some cases, they can be applied to both greenware and bisqueware.)

Besides liquid underglazes, there are increasing options available for underglaze application. These include underglaze pencils, crayons, chalk, and semi-moist pads which can be used like watercolors.

Underglaze Product Reviews

Amaco's semi-moist underglaze pans allow for effects very similar to watercolors done on paper.
Photo © 2009 Beth E Peterson
The following products have been used and reviewed by the Pottery Guide.

Slips

Pinch pot with slip decoration, using three different colored slips and loose sgraffito.
Photo © 2008 Beth E Peterson
Slips have been used since prehistoric times as a pottery decoration. Slip is, at its heart, basically nothing more than clay particles suspended in water. Since there are many naturally occurring colors of clay, the earliest slips were able to add several distinctive colors to the pottery they adorned.

Slip can be used in a wide number of techniques, from simple brushed on patterns to the bas-relief embellishments of paste-on-paste.

Stains

Label your pottery materials to avoid confusion and accidents.
Photo © 2008 Beth E Peterson

At their simplest, stains are raw ceramic pigments suspended in water. Commercial stains are carefully prepared and blended so that pigments are consistent and reliable in color and how they handle.

If you are use raw oxides or carbonates to make your own stains, be sure to use a respirator and rubber gloves as you work with them. Find out which raw materials are hazardous, and how to handle them safely.

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