ALL ABOUT UNDERGLAZES
Underglaze: Color pigment or chemicals suspended in a liquid applied to ceramic clay or bisque and fired with a finishing glaze topcoat.
There are several kinds of underglazes on the market. Some have been formulated to go on greenware and others have been formulated to go on bisq. It is important that you read the labels of your paints to know which is which and which ones are suitable for your project. This will also allow you to determine the method to complete your project on the paints you have available.
If you know what you want as a final outcome, you can go through various product lines to match color choices, compatibility of colors, and the process of application. If you don’t have some kind of idea, it would behoove you to do some research and find what you want before you start painting.
Underglazes allow you the most flexibility to create fine detail and design-work and are fun to use once you know the functions and applications of the various products. Underglazes do not flow like most glazes do.
Underglazes are exactly what they are named. They go UNDER a glaze, most usually a clear glaze; however transparent and semi-transparent glazes create some beautiful results with underglazes.
Most usually, underglazes that go on greenware have a clay base and bond with the greenware. If painted on bisque, they can peel off prior to or during any of the firing process. Underglazes that go on bisq are in a synthetic base and can grip or bond to the bisque.
Most underglazes do not achieve their intended color brightness or intensity until after they have been fired with a glaze topcoat. Of course, those that are a clay base will never achieve a shine. Some of the newer underglazes on the market actually have a ground glass/powder base(silica) and they will achieve a level of shine and brightness without the top glaze; however they have a greater sheen and color intensity with the glaze finish. Also, the glaze can ensure the item is food safe.
Most underglazes are not water tight without the use of a top glaze. So, in choosing how you finish your item, you need to determine its ultimate use.
Underglazes that are applied to greenware must be fired BEFORE applying the glazes. There are too many things that can go wrong if you try to get away with just one firing. See “ABOUT GLAZES”
Over the past 10-15 years, there have been so many changes in the industry spurred by EPA that current products made in the USA are lead free and much safer to work with than before. However, there are a lot of the old products still on the market (non-retail outlets) which are still usable. Application techniques have also changed with the advent of new formulas, so if you find you are using old product, do some research so you know the differences. Please be assured that the majority are still safe to use.
Older products may have lost some of their color intensity, so do be prepared for some slight disappointments. You may want to make some test chips to see how the color has held up before using them on a chosen item.
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