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Fire-Red is an unusual material for several reasons. It has a high iron content yet is a fireclay. It is also non-plastic. Most important, it is not ground to 200 mesh like industrial materials. These bodies demonstrate it well, left: 42.5% Fire-Red, 42.5% ball clay and 15% Custer feldspar, right: 60% Fire-Red, 30% ball clay and 10% feldspar. The ball clay adds plasticity. The feldspar gives control of the degree of vitrification (the left one has 1.3% porosity at cone 10R, the right one 1.5%). This recipe vitrifies so it does not exhibit the deep red color that Fire-Red would give if there was no feldspar. Look closely at the surface: It is covered by thousands of tiny iron-eruptions, they occurred as the iron pyrite particles liquify as FeO (because of the reduction atmosphere in the firing), and these produce a metallic appearance. And, they will bleed through an over-glaze, if present, to give stunning speckled surfaces.
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Fire-Red
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