Plainsman Clays | MACAL
Magnesium Carbonate Light
Magnesium carbonate is the way to add magnesia to a glaze without adding silica or calcium at the same time. More than half its weight leaves as gas during the firing.
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Magnesium carbonate adds no silica and no calcium, so it is the material to use where a recipe needs magnesia and nothing else. In small amounts it mattes a glaze. Magnesia grows fine crystals as the kiln cools, and those give the smooth, buttery surface it is known for. Colours shift towards pastels, and in a stoneware glaze with enough of it cobalt fires lavender instead of blue. In large amounts it crawls, and the trouble starts before the kiln. The powder is very fine and very bulky, it takes up a great deal of water, and the glaze layer shrinks and cracks as it dries, so the crawl can be seen in the dried glaze before anything is fired.
- Magnesia with very little else
- Gives a smooth buttery matte with pastel colours
- In large amounts it crawls, and the cracking starts as the glaze dries
- More than half its weight leaves as gas in the firing
