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Magnesium Sulphate - 1 lb.
Magnesium Sulphate - 1 lb.
Mg2SO4.7H2O. (16.36% MgO) Also known as Epsom Salts. Colorless transparent crystals. Some clay suppliers add hydrous magnesium sulfate (Epsom salts) to their clay mixes to improve plasticity and stabilize bodies against the thixotropic and spontaneous softening effects of certain soluble compounds in the mix (e.g. from soda feldspar, nepheline syenite). It is typical to use .2-.3%. Magnesium sulfate is also used to 'set' (flocculate, thicken, gel) glazes to suspend them and make them adhere to non-porous surfaces without running off. It forms a mild sulfuric acid that changes the electrostatic charge on clay particles causing them to reorient at right angles to each other. Thus it is typically added to glazes that have adequate clay particles for it to interact with. The most effective addition strategy is to make a saturated solution and add this in very small amounts to a slurry. If the crystals are added directly it takes time for them to dissolve and act and it is very easy to overdo it and thicken the slurry too much. Usually only about 0.1% is needed, but up to 0.5% can be used with particularly troublesome glazes. When evaluating how much is needed in a glaze slurry, be careful to give the added material time to dissolve. Epsom salts can be a helpful addition to glazes containing Gerstley Borate to help prevent particle agglomeration of a slurry that causes it to gel (try about 4 g per 100g of Gerstley Borate). Source: Digital Fire.
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