I have often had problems with flaking and peeling terra sig ever since I started pit firing. But since it doesn’t happen every time, I procrastinated in tracking down the root cause of the problem. Well, last Sunday I had a very successful firing — except for this flaking, peeling problem that happened to just about every pot I had in the pit, including some otherwise really gorgeous ones. Ouch!
Didn’t I say once that I learn more from my failures? So this time I fired up Google searching for “terra sig peel”, and found a bunch of great links on the Web:
- First and foremost is Vince Pitelka’s comprehensive treatise on the topic. This is a must-read for anyone working with terra sig. I wish I had read it when I first saw my terra sig peeling off back in 2002! :-(
- Clayart Forum thread "cracks in my terra sig"
- Clayart Forum thread "terra sig with no chipping/peeling"
- This article from CLAYART archive of Septermber 2001.
So what was my problem? Apparently I over-burnished my pots before I applied the terra sig, resulting in a poor bonding between the terra sig and the pot surface. And why did I sometimes get away with it, and sometimes not? My guess is that the degree of thermal stress and the presence of various chemicals played a role too.
I’ve noticed the peeling and flaking usually happens on the up side, i.e the side of the pot that was exposed to the flames, and not on the side buried in the sawdust or dung; it also tends to happen more frequently where there was a lot of fuming, often as a result of direct contact with salts or metal. The “quiet” side is generally quiet with terra sig peeling as well.
Anyway, time to start thinking about a new burnishing strategy…