Carbon Burnout Black Shadow Pottery

Blackened Patches On Pottery


Avoid carbon burnout problems on pottery.

Blackened glaze or patches of glaze in fired pieces are rare but can be a problem.

More commonly, this defect occurs:

  • On larger, thicker wares (air has to penetrate through the entire thickness of the piece and therefore it will take longer on a larger piece).
  • When a kiln has been fully-loaded or compact kiln (this is because there is not enough air in the kiln during firing for the carbon to properly burn out). 
  • A poorly ventilated kiln.
  • A kiln that was heated too quickly (so there was not enough time for the carbon to burn out).  Carbon which is only partially burned will continue to oxidize during the glaze firing causing defects
  • On pieces where the glaze viscosity is too thick.

View the document supplied by Orton Ceramics on how carbon burns out and what you can do to prevent an incomplete burnout.

CLICK HERE to view the PDF