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These two pieces are fired at cone 6. The base transparent glaze is the same (G2926B Plainsman transparent). The amount of encapsulated red stain is the same (11% Mason 6021 Dark Red). But two things are different. Number 1: 2% zircon has been added to the upper glaze. The stain manufacturers recommend this, saying that it makes for brighter color. However that is not what we see here. What we do see is the particles of unmelting zircon are acting as seed and collection points for the bubbles (the larger ones produced are escaping). Number 2: The firing schedule. The top one has been fired to approach cone 6 and 100F/hr, held for five minutes at 2200F (cone 6 as verified in our kiln by cones), dropped quickly to 2100F and held for 30 minutes.
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