What Is An Underglaze? Definition And How To Use It

Underglazes are commonly applied underneath another glaze which creates designs and patterns that come up through another layer of glazing that covers it. This can give the surface more visual depth and character. Underglaze is generally used under clear glaze, but they can also be used under other light colored but virtually transparent glazes.

What is the difference between glaze and underglaze?

Underglaze and glaze can both be used as a form of decoration for pottery pieces.  The difference between a glaze and an underglaze is that an underglaze is applied before a clear glaze.  An underglaze can be used to create a unique and different design, whilst a clear glaze placed over will help to seal the piece and make it non porous.

What is the difference between underglaze and overglaze?

The difference between underglaze and overglaze is usually expressed by their visual finish - specifically by the colors of the finished porcelain. The color spectrum is much larger in the overglaze technique than in the underglaze technique. This is because of the chemical reaction when the glaze is heated. The colors dissolve at different temperatures and underglaze uses a much higher temperature than overglaze. When looking for underglazes and overglazes, you'll find many more colors in overglazes than underglazes.

What is underglaze made out of?

Underglazes are made from a mix of clay, colorant and water. These need to be added to the piece in several layers of paint to ensure the colors/ patterns are not transparent after firing and the color is detailed and vivid enough once fired.

What type of underglazes can be used?

When the piece is damp, potter-made slips (made of a thin clay and water mixture) can be applied. Potter-made engobes (a mixture of silica and glass) can be applied to pots that have been bisqued. And traditional underglazes (comprised of colored oxides) can be applied to greenware.

Underglazing Greenware

The first thing you should do when underglazing greenware is place your dried piece onto your potter's wheel. Next, make circular marks with a pencil or similar in the positions you would like the underglaze to be applied . You can apply the glaze over your marks whilst turning your wheel.

Applying the underglaze to greenware enables you to see what the design will look like when finished, which makes it easier for you to make adjustments to the final design . You can use a much wider selection of colors with greenware than you can with bisque ware.

Underglazing Bisque Ware

The main advantage of underglazing to a bisqued piece is that it will not ruin the clay or the clay won't dissolve out from under your design. When underglazing a bisque piece, you can also use tools in the process, without harming the piece. You can use a range of instruments such as underglaze pencils or pens that will not affect the surface of the piece and creates a more precise design.

To underglaze a bisqued piece, hold it with a clean cloth. Apply your chosen color or colors as though painting on a canvas. Layer your colors so that your end product is vibrant and creates a striking design. You can layer up to 6 coats to get your required finish. Once you are satisfied, you can apply an overglaze and fire your piece to seal.

Why is underglaze used?

Potters use underglaze because it allows more fluidity with designs, allowing the artist to add extra color and detail. It also makes it possible to apply an underglaze to a clay mould, bisque fire it and then proceed to add more color and design elements before applying a final glaze, which produces some real unique pottery pieces.

Underglaze can also be easier to apply with a brush than overglaze, making it easier to create intricate designs. This makes the final product outcome easier to control as you can be more accurate with how the glaze is applied.

Additionally, the color of unfired underglaze is similar to its color once it has been fired, so you can clearly see what the final product is likely to look like. The control of being able to see what a piece will look like before it has been fired is of great benefit for ceramic producers.

This is opposed to overglaze, which often looks very different before it has been fired than afterward. It's more difficult to control and you can't really tell what the glaze will actually look like until it has been fired in the kiln and is dry, which requires much more trial and error.

How can underglaze be applied?

As mentioned previously, underglaze is commonly applied using a pencil or similar craft tool, as this is the best way for an intricate design to be created. However, other techniques to apply underglaze include:

• Dipping the ware in glaze

• Painted on glaze coat

• Pouring the glaze on the ware

• Spraying the glaze with an airbrush

• Sponging on the glaze

Ultimately, the method that you use is dependent on the effect you want to create.

Summary

Underglazes provide much more flexibility in terms of design in comparison to overglazing. If you are looking to create pieces for commercial purposes, then it's best to test out different layers of underglaze and test firing to ensure that you are completely comfortable with the finished outcome.

You will also need a kiln to fire your glaze, whichever method you choose. Soul Ceramics have a wide selection of electric kilns, perfect for glazing, which you can view here. Also check out our range of glazes and underglazes here.