Expert: Sam Kelly - 4/22/2009

Question
Sam,
I have been given a prepared commercial glaze called Forest Green opaque made by Laguna Clays. It was mixed long ago but I have sieved and thinned it to good coverage. The problem is that it sometimes leaves "pinholes" especially where the pot was trimmed. I rib and sometimes sponge the trimmed areas on my pots if needed until they are smooth and this does seem to be the only glaze causing problems. I have a bit of wollastonite and was wondering if an addition of that would help solve the problem. I do not know the original composition of the glaze since it is commercially prepared. There is about 2 gallons of glaze which should mean 1.5 - 2 lbs or so of dry mix would remain if I magically sucked all the water out. How much would I add and do you think it would help?

Answer
Hi terri, pinholes are the hardest to get rid of. make sure the rim is as round as it can be, reduce the curvature angle as low as possible, in other words no sharp angles, this is where the pinholeing seems to like to start.

Another test is to wash the pot after bisque, dry out and apply the glaze.

Measure out 150mills of your glaze and test with 5grams and 10grams of wollastonite. This will be close to 5 and 10 % additions.

sam