These are various different terra cotta clays fired to cone 04 (also a low fire white-buff fritted stoneware) with a recipe I formulated to source the same chemistry as the popular Worthington clear, but sourcing the B2O3 from Ulexite and a frit instead of Gerstley Borate (G2931B). All pieces are fired with a soak-soak-slow cool firing. Fit is good on all except a fritted terra cotta stoneware where it is shivering slightly (all were boil:ice tested). This outlines work I am doing to create an alternative recipe for the popular 50:30:20 GB:EPK:Silica recipe (Worthington clear) that uses Ulexite instead of Gerstley Borate (the later is notorious for turning glaze slurries into jelly!).
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