Home > Cone 5 & 6 ox, oil spot, Oxidation > Oil Spot ^6 John Britt –Mimi Champlin

Oil Spot ^6 John Britt –Mimi Champlin

  •  ^6 Oil Spot glaze from a John Britt workshop. Fires in oxidation.

    Oil Spot Combo #1 (three coats), specific gravity 165
    G-200 feldspar: 47.83%
    Silica: 23.91%
    Whiting: 17.39%
    EPK: 10.87%
    Red Iron Oxide: 9.78%

    Oil Spot Combo #2 — Cover glaze (apply over #1) (two coats)
    Custar feldspar: 30%
    Gerstley Borate: 30%
    Silica: 25%
    EPK: 5%
    Zircopax: 10%

     The mechanism of traditional oil spot (which is high fire, not Cone 6 range) is based on the instability of the red iron oxide molecule above about 2250 F. Orton Cone 6, if you are using the large cones, is going to barely reach that temperature. The slower you fire the LOWER the end point temperature will be at any given cone. (Remember, cones measure heat work, not tmperature.) At 270F per hour rise, Cone 6 end-point is 2266-ish F. So it will start to break the bonds…. but it is “close”.
  • I’d suggest that you fire the last about 200 F of the up cycle at a fast rate………like 270 to 300 F per hour (if your kiln will do it). That will make sure that you end at a “hot” remperature for the Cone 6 dropping. Then play with the soak period at the end to allow time for the evolution of the oxygen gas to bubble out of the underlying glaze layer and bring the “spots” to the surface. It will require some testing for you to see how long a soak gives you what type/size of spots.
    This is info from a conversation on ceramic art daily, by John Baymore http://www.JohnBaymore.com/
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