WarmGlass.com

I put a 3mm Bullseye screen-printed 3 1/2 in square piece in my Paragon Caldera to fire. Went full to 1050 with a 10 minute hold. Then my schedule is full to 1465. However, at about 1100 I looked through the peephole to see how the enamel was looking and saw black specks all over the piece and shelf paper. I immediately turned it off completely figuring the piece was ruined. My experience is that kiln crap gets embedded into the glass.

When I took the piece out I found that the specks brushed off nicely. I'm wondering if I can refire the piece or is the integrity of the piece compromised because i did not do a regular anneal?

Thanks so much.
Drewcilla

No problem with refiring.

Also, a 3mm piece of glass will anneal just fine cooling gradually through the annealing range.

Thanks Brad.

Better find out what the black specks are and eliminate them. While they won't embed in the glass at 1100, they will at 1465.

Warren

I'd think that the black specs were ash that came from the SHELF PAPER. This likely happens every time you use shelf paper but completely burns out by the time you see the finished results.

I know that thinfire turns black around 800 f and goes back to white at higher temperatures. I never noticed it deposit on the glass.

Warren

Warren Weiss wrote:Better find out what the black specks are and eliminate them. While they won't embed in the glass at 1100, they will at 1465.

Warren

By 1465, they have burned up. Carbon with heat and oxygen, vaporizes. I have seen it stick in a situation where there is no oxygen, only heat. (that would be under very large sheets of glass) But the general rule is no sticking.

Bert,

If pure carbon, you are surely correct. If it is black rust it is another story. Just saying that I have never seen carbon from thin fire deposit on the glass, but I suppose it could.

Warren

Warren Weiss wrote:Bert,

If pure carbon, you are surely correct. If it is black rust it is another story. Just saying that I have never seen carbon from thin fire deposit on the glass, but I suppose it could.

Warren

I have seen carbon from Unifrax 970 paper make permanent marks on glass. It was on large sheets. I prefire when making complex patterns on large sheets, using fiber papers.