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Sunday, July 20, 2008

Naked Raku 102

After the bisque firing, we prepared for the final firing. All of this work took place on the final class.

We coated our pots with a special crackle slip that's made to shrink. This makes it crack up and peel a bit during the firing and smoking process, like a mud puddle in the summertime. It won't actually melt and bond to the pot in the firing, and it will be scraped off afterward. Any larger areas we wanted to be black were left bare. Some people left the rims and collars exposed, or a design on the pot itself.

Then a thin 'glaze' is brushed onto the slip coating. It's job is to try and hold the slip together through the firing. You don't want to get it on any exposed areas of the pot, since it will bond to the clay and makes an ugly blistery mess. Unless that's the look you're going for.

The pots are fired to temperature, which is done more by feel than anything, observing how the surface looks and how the glaze is melting. They are then pulled out and placed in a metal can with sawdust or similar in the bottom. This instantly ignites, and after the flames are going good, an airtight lid is clamped in place. This makes the fire smoke, and this smoke penetrates the clay where the cracks in the slip coating are. After the pot cools, the lid is carefully opened since once air is allowed back in a flare up is very possible if the pot is still hot enough. The still hot pot is sprayed with water which helps crack off the slip/glaze coating now that it's job is done.

We finished by scraping off the slip/glaze coat with metal ribs. After they had dried off the burnished pots could be waxed and buffed with a hard paste wax.

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