Very low specific gravities on two commercial underglazes

Thursday 26th April 2018

AMACO and Crysanthos. 1.26 (67.5% water) and 1.22 (68% water)! The former is well below their recommended insight-live.com/glossary/86">specific gravity of 1.4 (it still paints well but needs more coats and more time to dry and apply them). The Crysanthos, although having a lower specific gravity is more viscous and goes on thicker (so it likely contains more gelling agent). When doing underglaze decorative brushwork it is important to get adequate thickness with eachbrush stroke, so a higher specific gravity is better. This may be reason enough to consider making your own (by adding stain powders to a base and using Veegum CER to gel the slurry, slow down its drying and harden it well at the dried state).

Pages that reference this post in the Digitalfire Reference Library:

The glaze firing reveals that the specific gravity of this V-303 terra cotta under glaze is too low, Black is a case where making our own underglaze makes sense, AMACO recommended specific gravities for Potters Choice glazes, Underglaze, Specific gravity, Brushing Glaze

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