Same cone 6 glazes. Same clay. Why is the one on the right pinholing?

Monday 27th May 2013

These are thick pieces, they need time for heat to penetrate. Both were soaked 15 minutes at cone 6 (2195F in our test kiln). But the one on the left was control-cooled to 2095F degrees and soaked 45 more minutes. Pinholes and dimples are gone, the clay is more mature and the glaze is glossier and melted better. Why is this better than just soaking longer at cone 6? As the temperature rises the mineral particles decompose and generate gases (e.g. CO2, SO4). These need to bubble through the glaze. But on the way down this activity is ceasing. Whatever is gassing and creating the pinholes will has stopped by 2095F. Also, these are boron-fluxed glazes, they stay fluid all the way down to 1900F (so you could drop even further before soaking).

Pages that reference this post in the Digitalfire Reference Database:

Electric Hobby Kilns: What You Need to Know, Soaking, Glaze Pinholes, Pitting, Cone 6 Drop-and-Soak Firing Schedule

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