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SaraDrury

Glaze Problem

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I am having problems with my glaze chipping or flaking off after firing.  I am using Amaco No 25 white art clay and firing to Cone 05.  I am using Potter's Choice pre-mixed liquid glaze PC-46 and firing to cone 5 1/2.  I am brushing on 2-3 coats of the glaze with no other layers or underglazes. I have a very small manual kiln and have consistently had an issue with the glaze flaking off the edge of handles, rim or foot of the pieces I am making. I am not sure if this is a problem with the clay body, firing, glaze or some combination.  I'm attaching a picture of an example. Any suggestions are appreciated! Thanks!

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This is called shivering and it is caused by a difference in the rate of expansion/contraction between the clay/glaze. In this case the glaze is too big for the clay and because it is glassy out breaks when the clay contracts to its final size.

I'm not familiar with this clay or glaze. Do the manufacturers publish coefficient of expansion numbers(COE for short) for this clay/glaze?

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Looks like that clay is not meant to fire to cone 5. Amaco lists its max temperature as cone 3. You'll need a different clay if you want to use that glaze and vice versa.

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Amaco #25 clay is a 05 low fire clay. Potter's choice glazes are cone 5-6. They are probably incompatible even though Amaco says the clay could be fired to cone 3. I get great results with Amaco Artist Choice low fire glazes with this clay.

 

- Paul

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