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Michael Slack is at it again. He is using a modified Zero4 recipe for knapping: 3 parts Frit 3110, 2 parts Georgia kaolin and 1 part silica (by volume). Whatever the weight is, he adds 3% bentonite. This develops the required density and hardness by 1045C.

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Wikipedia terms Knapping as “the shaping of flint, chert, obsidian, or other conchoidal fracturing stone through the process of lithic reduction to manufacture .. flat-faced stones.” In other words, it is the process of carefully breaking off pieces to create sharp edges and controlled surfaces.
Knapping is a thing. r/Knapping on Reddit has 12k followers. There are lots of YouTube videos, articles and books, websites and even commercial suppliers. Michael Slack has answered the question: Could Zero4 porcelain be knapped? The answer, as you can see, is: Nicely. This is not an arrowhead but a proof of concept biface. Michael was motivated after seeing the glassy internal structure of the fired material. He used 0.3% cobalt, thus the blue color. If you attempt this be advised of the importance of extremely vigorous mixing of the slurry to remove all agglomerates. Try various temperatures to find the most knappable material.
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