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Strange airborne particles in kiln


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Had two stoneware electric kiln glaze fires this week. Both using clays and glazes I've used before. Dark blue or black particles have appeared on some pots. Inside and out. On different shelves. Some shelves only one pot affected. Some none. Definitely airborne by the way it has landed on different parts. Seems honeycomb in texture. I hoovered the kiln before firing.  I used a clear glaze over underglazes and slip. A white glaze with cobalt oxide over. And some over glazes applied on unfired clear or white glaze. I thought it was the cobalt after the first firing but the second firing they weren't affected.   Any advice or ideas would be greatly appreciated. Thanks.

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  • 2 weeks later...

try an experiment.  before closing the lid, put a piece of paper large enough to span the opening on top.  white gift wrap on a roller works fine.  close the lid the way you normally do.

open the lid and look at the paper.  if there are dark spots, the edge of the lid may need some stiff brushing and vacuuming before your next firing.  check right where the metal band touches the firebrick.

the stress put on the lid as it is opened and closed can cause tiny bits to fall into the kiln.  some are very light and can be moved by air moving across the  kiln shelves as they heat.

Edited by oldlady
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Anyone mixing or stirring glazes where your glazed ware is sitting? 

Any granules in your glazes?

I can understand the black brown bits coming from the kiln lid or edges but the specks of blue suggest contamination coming from elsewhere. A fugitive lurking in the kiln would be more likely to tint a glaze than speckle it, imo

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