by Shona Cameron
I have crazing of my glaze a couple of weeks after firing.
I am using a white earthenware clay which has good plasticitity-fires between 1060-1160deg C. The glaze is a transparent leadless glaze firing between 1020-1080deg C.
I have been bisque firing at 1065deg and glaze firing at 1050deg. At the moment I am re-firing the glaze to 1065deg but if this doesn't work should i try adding silica to the glaze? I feel quite despondent about it all even though I know that's a negative unhelpful attitude!!
Thanks a lot,
First, I'm sorry to hear about your craze frustrations. I can relate all to well. I've had a lot of struggles with glazes and clays not "fitting" together. In fact, you may have noticed that most of my information on the site is geared toward forming clay and then using commercially prepared glazes.
The reason for this is that glaze formulation is very scientific and I'm more of a free spirit, -read as I hate math:). I've tried it, and it just wasn't my thing.
That being said, if you are formulating your own glaze, it is a matter of going back to the drawing board and testing, testing, testing. By the way, if you are formulating your own glazes, I commend you, just keep your scientist hat on and remember that it takes patience and testing. You truly are creating.
On the other hand, if you are buying clay and glazes, check with the manufacturer to make sure that the recommended CONE temperature is compatible in both.
You referred to your FIRING temperature, but that isn't really a great measure of the "heat work", which is temperature PLUS time, that is being applied to the ware. CONES will give you a more accurate measure of heat work and therefore a more accurate measure of how compatible clay and glaze truly are.
Also, here is a great article that says all of this much better than I have. Plus, it addresses your mention of adding silica. Check it out.