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redbourn

Clear Glaze Over Underglaze Makes Underglaze Run

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Hi Friends,

 

I was able to participate in a Lana Wilson workshop recently, where we made slabs with layers of underglazes on top, then scratched through and stretched. The slabs were lovely, and I made a small tray out of half of one of them. Bisque fired it, then applied a commercial clear satin glaze, fired to cone 6.  The result was that the glaze made the underglazes run and soften a bit. An attractive result, but with the other half, which is a wall piece, I don't want the softening and running. A potter I met told me she seals her slip-transfer wares with a gerstley borate wash.  Would this work for my slab, coated with underglaze, do you think? Other suggestions?  I'd like a matte to satin finish.  Thanks in advance, Lynn

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I think it was the underglazes made the glaze run. A gerstley borate wash would work, but you should test.

Could the commercial glazes have been on too thick? Could it be you hit a hot ^6. Did you soak. Possibly the clear glaze doesn't need a soak. There are a lot of things that could have happened.

 

Marcia

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Underglazes will bleed out differently with different clear glazes. A lot of clear glazes are somewhat fluid, but it's hard to tell because they're clear. Others will tend to pick up the underglaze more than others. Test, test, test....

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These are all very helpful responses--thanks!  As to the wall piece, I'll take Chris Campbells' suggestion.  As to clear glazes, I guess the answer is to test, test, test.  Lana Wilson gave us glaze recipes, but she uses a different clay body and different firing schedule than what I have access to.

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Are you using Amaco Velvets underglaze with their glazes? I've used both the HF-9 zinc free clear gloss and the HF-12 satin with the Velvets without any running, though the Satin did soften the colors and turned a bit cloudy because I applied too heavily.

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