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why_not

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  1. The saggar has a tight seal to prevent carbon monoxide from escaping which both ensures strong reduction and protects the kiln elements but it prevents oxygen , from the atmosphere , from entering so a source of oxygen must be provided. The iron oxide is added to provide a source of oxygen to react with the carbon . Black iron oxide was chosen because, at temperatures around cone 6, it reacts easily with carbon to produce carbon monoxide. Black copper oxide could also be used as an oxygen source but it's more expensive. Black iron oxide is cheap, readily available and comes as a very fine powder. To protect the saggar, the iron oxide and charcoal are placed on a tile which sits in the base. Residue from the reaction can be easily scraped from the tile so it can be reused and it can be replaced if damaged. The aim was to make the saggar last as long as possible. Thank you for your responses. Also my complements to Marcia Selsor for your excellent cone 6 copper red glaze!
  2. I have recently carried some successful trials using saggars to produce cone 6 copper red reduction glazes in an electric kiln. I generated a reduction atmosphere by adding a small amount of black iron oxide mixed with powdered charcoal to the bottom of a saggar with a test piece painted with Selsor red copper reduction glaze (see formula in "The Complete Guide to Mid-range Glazes " by J. Britt pg 100). I started with a copper red cone 6 glaze because it is easy to see if there is reduction; red=reduction / green=no reduction. The iron oxide/ charcoal mixture reacted to produce a reducing carbon monoxide atmosphere within the saggar, as the electric kiln was fired to cone 6, which changed the glaze oxblood red (see attached photo). The atmosphere in the kiln remained oxidizing so that test patchs of the same glaze painted on the outside of saggar remained green. I hope that by sharing these results I can generate feedback on this this technique.
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