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black discoloration

For discussion of processes related to using Bullseye glass, including kilnforming and kilncasting, torchwork, blowing and stained glass.

black discoloration

Postby Roberta Ayles » Mon Jul 22, 2019 6:33 am

20190624_173240 (1).jpg
discolored area
20190624_173240 (1).jpg (189.99 KiB) Viewed 384 times

This piece was fired on a textured surface of bio-soluble fibre paper, kilnwash and plaster, on a ceramic fibreboard shelf. I used various blue frit capped with 6mm Tekta. I suspect the plaster/kilnwash texturing was still damp, as the darkening has happened in the area of deepest texture, and the color is unaffected near the edges, where moisture could escape. I don't usually dry the texture before firing, but am in a temporary workshop and think there is less circulation of air and warmth than in my previous workshop. When I wetted the plaster mix to clean it off the fired panel, it gave off a sufurous, rotten egg smell, and there is a stain on the fibreboard shelf too.
Has anyone else come across this dark staining, or have any alternative thoughts as to what might have caused it? I also wonder whether the shelf will be safe to use again?
Roberta Ayles
 
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