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Amaco Velvet underglazes fire to a pleasant velvet surface at cone 6 achieving good opacity and coverage. However, at cone 04 the surface is dry. Could the velvet appearance be achieved there? These cone 05 bisque fired Buffstone tiles have a single coat of V-308 Radiant Red topped by a single layer of G1916QL1 clear brushing. Spectrum 700 transparent low-fire glaze has been liquid volume blended at a 9:1, 8:1 and 7:1 (V-308:S700). Notice that as more glaze is added the color actually darkens! By 7:1 the surface is velvety. 8:1 seems optimal (because 7:1 is losing opacity). But caution is needed because the higher the glaze percentage the greater the fired shrinkage misfit between underglaze and body (misfit is not tolerated as well at low temperatures because the bond with body is not as intimate). So a conservative mix 9:1 would be a better starting point. A side-effect is that adding the glaze may change the underglaze’s rheology (so a deflocculant or gelling agent might be needed to establish thixotropy).
Top are V-326 and V-388 underglazes, painted on and bisque fired at cone 04. Although the layer is thin the coverage is very good and the brightness is stunning. How can these colors be so bright? Using very high, and expensive, percentages of stain. That explains why these commercial underglazes are double or triple the cost of a typical commercial glaze. The bottom mugs are clear-glazed and fired at cone 05, the one on the left with Amaco LG-10, The one on the right is Spectrum 700. The latter produces better results over the underglaze and is more transparent and less yellowish on the body.
Can you make bright-colored engobes and underglazes like this? Yes. Start with 50% stain and 50% stain medium (the percentage needed varies by color and type of stain).
URLs |
https://www.amaco.com/t/glazes-and-underglazes/underglaze/velvet-underglaze/velvet-underglazes
AMACO Velvet Underglazes, a traditional non-melting product meant for use under a transparent overglaze. Velvet underglazes fire true-to-color from cone 05/06 to Cone 6 (some till cone 10). Their name comes from the surface quality when fired to cone 6. The formulations have a high percentage of stain and are thus saturated, this enables good coverage even if applied thinnly. This product line has a good reputation for consistency, documentation and flexibility. |
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Glossary |
Underglaze
An intensely pigmented highly opaque non-melting ceramic material mix meant to adhere best to leather hard pottery and fire-fit the body. Often transparently overglazed. Starter recipes. |
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