How to Calcify Kaolin #pottery #clay #shorts #ceramics

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Calcifying Kaolin
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When it comes to creating a successful glaze recipe, there are many factors to consider.
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Adding more clay to a glaze recipe, is a great way to bring the alumina levels up, alumina is a glass former, and a correct amount is needed to stiffen the glaze, the problem is if you add to much clay, you also invite more clay shrinkage.
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Kaolin clay as with of all clays tend to shrink when fired, which can cause problems, such as crawling. Fortunately, there are ways to stop this shrinkage and create a more suitable glaze.
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Solution is to either purchase calcified kaolin or make your own.
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When kaolin is fired, the chemical bound water molecules in the clay structure start to
evaporate, causing the kaolin to shrink. Calcifying kaolin before you add to
glaze recipe drives out the chemical bound water, preshrinking the kaolin.
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Once kaolin is calcified it will not shrink any more, you can add more clay to the glaze recipe without the worry of excessive shrinkage.
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How to Calcify Kaolin
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Step 1
Take a bisque pot and fill with kaolin, always use a protective full-face mask when handling dry glaze materials.
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Step 2
Put your filled pot into the kiln with other pots to be bisque fired, and fire to bisque temperature.
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Step 3
Remove your pot of calcined kaolin and put it into a lidded container, a word of caution, the calcined kaolin now is lighter and also very powdery so when disturbed the particles will become air bourn, so make sure to handle with Care and always wear your full-face mask.
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Step 4
Label and store your calcined kaolin in a dry place ready for you to use the next time you need to add more clay but are wary of shrinkage.
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Happy Potting 😃