iandol on tue 2 jan 01
Carbon Trap Theory 1
I consider it most probable, after reading about the chemistry of the =
Carbon gases, that this effect will occur to the greatest degree at a =
temperature of about 600 deg C (1112 F). As temperature rises from this =
point, the rate at which carbon will form in a clay or glaze will =
diminish towards a minimum when the pottery reaches 1000 deg C (1864 F). =
Above this temperature the reverse reaction will take place if kiln gas =
rich in Carbon dioxide can diffuse into clay or glaze.
The following suggestions may guide people who wish to attempt this =
style of firing.
There seems to be a need for a low melting point flux in either clay or =
glaze to seal the surface against further diffusion before the =
temperature reaches 1000 deg C (1112 F). This will help to preserve =
carbon which has been deposited.
The chemical reaction which creates the Carbon responds better in the =
presence of Iron oxide in the clay or the glaze but the amount needed =
may be relatively small.
The kiln atmosphere must contain appreciable quantities of Carbon =
monoxide for the full duration of the treatment.
Glazes which remain porous may respond to a Carbon monoxide rich =
atmosphere during their cooling cycle between the upper and lower =
temperature limits.
These suppositions require experimental and analytical validation.
Ivor Lewis. Redhill, South Australia.
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