candleing

Sandi: I know potters that candle for three to five days. If you really want to drive the moisture (the free moisture, not the moisture interlocked in the clay molecules) out of the clay, candle at 150 or 200 for a day or so, and then raise the temp to the boiling point of water (212 F or 100C) and let it candle there for a few hours. Then fire or bisque as you normally would.

Of course, it depends on the temp to which you end-fire (is it a low fire or high-fire clay body you're using?), but generally speaking, heating to that low a temperature will not harm the clay.

Also, if you have had "pieces explode in bisque", it may have been from air trapped in clay, and not moisture. If it ever happens again, or if you still have the pieces as a "reminder" from last time, examine the edges of the cracks closely for sign of air pockets. If there are none, it will have been moisture that was the problem after all.

I regularly dry pieces in my electric with one element set on low for a few hours, then another element in addition set to low for a few more hours, or overnight, if the pieces were really wet. Depending on what the temperature is when that's finished determines how fast I raise the temp afterward. I slow down around 100C (212F) which is water's boiling point, and again through 600C which is the range for silica conversion.

Hope that helps,

Thanks Wayne, Your answer was great. It helps me alot. I usually fire to cone 6. Do you know if candleing for days would cause your pots to be more prone to cracking on the bottom than letting them air dry for days on the ware shelf at room temp? I use a clay that is nortorious for cracking bottoms if you don't compress really well. (#112) Sometimes if the piece goes into the kiln intact it will come out of bisque with a crack in the bottom. I guess what I am wondering is if candleing is a more even drying than air drying? Thanks, Sandi

i think candling is a much better way to fully dry a pot then just leaving it sit to air dry. there is a flow of hot dry air all around the kiln. you don't get this sitting out even in a breaze.

keep in mind too that "dry" might mean no water in the clay, but it's not

*really* dry until around 400°F when even the water boiled off truly leaves the pot.

you can candle a long time but you'll reach a point where you're simply wasting heat rtaher then drying out the pots.

i gage this by watching the temperature. if i hit 300°F after candling a while i go ahead with the fire. otherwise it can get expensive on the gas bill.

steve

steve graber