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chemistry questions: clay discoloration & glaze thinning

updated sun 20 jun 04

 

Barbara Kobler on sat 19 jun 04


Hi all. Your help will be appreciated in answering these two questions:

1. A few days ago I sanded down 4 greenware pieces made with red clays that had intricate coloured clay inlays. I made pieces out of each of Laguna's clays--SB red, Amador and Los Altos. I took them out of bisque fire today. The surfaces of all the clays look as if they had been rubbed with a beige powder. I wanted to leave these pots unglazed, but they are really unattractive with this beige discoloration. This is a new technique for me. How can I avoid it in the future. I have to sand them to expose the colored clay designs. What do you suggest?


2. I remember reading that in glazes that contain_________(fill in the blank) chemicals, they tend to get thinner after a couple of days. I have one like that and simply draw off excess water after a couple of days but want to know which chemical it is that can cause this result.
Thanks
Barbara Kobler http://www.claywoman.net