POCA
A soluble source of potash that brings no alumina or silica · Goes into synthetic ash glazes and self-glazing bodies · It travels with the water rather than staying in the slurry · It draws moisture from the air, so an old bag is short on potash
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Potassium carbonate, long known as pearl ash, is a soluble alkali that carries potash into a melt with no alumina or silica attached. It goes into synthetic ash glazes, and into bodies meant to glaze themselves as they dry.
Potassium carbonate dissolves rather than sitting in the slurry as a powder, and that changes where it ends up: it soaks into a bisque wall with the water, or comes to the surface of a drying pot as the water leaves. A self-glazing body is built on exactly that migration. In a high-alkali, low-alumina glaze it pushes copper toward turquoise and cobalt toward a more brilliant blue. It also draws water and carbon dioxide out of the air, so an opened bag in a humid room cakes, and a batch weighed from it comes up short on potash.
