A great deal of the answers to these questions lie in what products or supplies you are using. Potter-made slips should be applied while the clay is damp. Potter-made engobes (an engobe is basically a non-slip glaze) should be applied to bisqueware. However, commercially made underglazes are usually formulated to be able to handle a wider range of shrinkage... or lack thereof.
Underglazes are defined as colored slips that are applied to a piece before it is glazed. The color range of underglazes is usually vast and a whole range of techniques can be created.
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Check Your Underglaze
Commercially produced underglazes are usually able to be used on either greenware (generally considered to be bone-dry greenware) or bisqueware. Check the labels of your specific underglaze product for further information.
One advantage of commercial underglazes is that they can also be used both before and after bisqueing. You can begin with an underglaze design on greenware, bisque it, then may add more color or detail with underglazes again before applying the glaze coat.
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Advantages to Underglazing Greenware
- After bisqueing, the underglaze will not lift into the glaze during application, even if you brush glaze on
- Doing it then allows you to see the close-to-finished design, so you can see if you want to darken color depth or make additions.
- You can use a far wider underglaze range (color wise) with greenware than you can with bisqueware.
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Advantages to Underglazing Bisqueware
- Even heavy or wet applications of underglaze will not harm the clay or dissolve it out from under you, so to speak. This is especially useful if you are using watercolor-style underglazes.
- You can be a lot rougher with the underglazing process, for example, using underglaze pencils, crayons, or pens. Drawing with a pointed underglaze product will not dent, incise or harm the clay surface and will give a more precise design.
- The bisque work is usually very plain so you will be able to see exactly... what you are working with.
- Underglaze tends to run a little less than than overglaze, again another reason you can do intricate patterns.
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What is a commercial glaze?
If you want to use a commerical underglaze you can pick almost every color you can think of, as they are basically made up of clay slips with different colorants inside.
They are many different ways of applying commercial glazes, like coating your pot in layers of underglaze and building them up very slowly. This will make the color even stronger.
Note that the difference when buying a commercial bisque underglaze is that they may have added more frit (frit is defined as 'a fused or... partially fused material used as a basis for glazes or enamels').
One of the benefits of using underglaze is that you are able to mix your own colors together. Something you are not able to do with regular glazes.Continue to 5 of 5 below.
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Decorating ideas with underglaze
The range of things you can do with underglazes is often limitless and the glazes themselves come in a range of different forms. For example, you can buy them in liquid form, dry form as chalks and even as pens and pencils, so you can be very detailed with your designs.
Unleash your creativity with your underglaze by trying out different techniques such as spraying the underglaze on gently, sponging it on and even flicking it on with a toothbrush for a splattered effect.
If you thin the... underglaze right down they can have an almost wash effect on the piece. Or you can paint with a variety of colors any pattern you want. You can think of the pot, plate or tile as your blank canvas.
Stencils are perfectly suited to underglaze. Either buy them from a craft shop or have a go at making your own with some thin cardboard and a stanley knife.
After you've underglazed your work you can overglaze in clear to give it a high shine finish. A clear glaze also works to seal in your pattern or design work.