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black discoloration

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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 9846 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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Re: black discoloration

Postby marykaynitchie » Wed Aug 21, 2019 12:08 pm

Hi Roberta,
While the photo is helpful, and you have described some of the process and materials, we will need more information to give you accurate advice.

What styles of blue frit did you use?
Can you give a more detailed description of which styles of glass contacted which shelf separator?
What project was previously fired on that shelf? Was the shelf primer removed and reapplied?

Mary Kay
Mary Kay Nitchie
Bullseye Glass Co.

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