Expert: Leisha Hiester - 2/16/2010

Question
Hi,
I have returned to making EP after a break of several years and am having difficulties in problem solving a few issues.
I seem to have been able to develop a base mix that fires well with a glossy surface to the bead. Firing to almost cone 04. However when I add copper carb or cobalt carb to the base to get turq and blue, the surface of the beads changes radically. The surface is still glassy but the texture is lumpy and grainy - as though it has not melted cohesively together. I have tried tweaking the base mix to increase/decrease silica, alumina and fluxes, but all that seems to achieve is more melting but the surfaces do  not change. my recipes consist of soda feldspa, silica, china clay, bentonite, soda bicarb, soda ash.
I tried a glaze stain in my last firing and the results were pretty good for those beads (I am keen to use the raw oxides though because I can get a better range of tones). I have spoken to a few people who have suggested it could be the cobalt and copper causing the  problem - or it could be the Soda Feldspa.
I mix the base dry and then weigh out small amounts to mix the colourants into. When ready I mix a small amount of water to the batch and work well (in a plastic bag) then let that sit overnight before making the beads.
In the past I had good results but my location has changed and thus all the raw ingredients I am using are new. Any thoughts/help would be greatly appreciated.
Thank you for your time, Celia.

Answer
Celia,
It's funny that you stated that you thought the cobalt or copper might be the problem. I was going to ask you if you changed suppliers or locations. I have lived all over the U.S. and in different climates and experienced similar issues. For instance, I started potting in Michigan where it is humid. I moved to Colorado which is an arid desert. I then lived in Hawaii where it is tropical. Each move I had to make adjustments.

Try obtaining a small amount of oxides from your old supplier if you can to rule out whether that is the problem.

I hope this helps. Feel free to write again. I'll be very interested to learn what you find out.

Leisha