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Norm Stuart

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Posts posted by Norm Stuart

  1. It could be that too much lead has evaporated from these ^6 glazes if you fire too slowly.

     

    I found a ceramics journal from 1904 which quantifies the percentage of the lead in a glaze, fired in a sagger, which vaporized per hour.

     

    Journal of the Society of Chemical Industry, Volume 23  - Society of Chemical Industry (Great Britain)  1904

    http://books.google.com/books?id=lkLOAAAAMAAJ&pg=PA470&dq=kiln+firing+%22lead+glaze%22+loss+per+hour&hl=en&sa=X&ei=qhTnUpKpAYPvoASxlIGoCw&ved=0CDsQ6AEwAA#v=onepage&q=kiln%20firing%20%22lead%20glaze%22%20loss%20per%20hour&f=false

     

    Without rereading it I think the volatilization of lead per hour at cone 6 was about 1/3 per hour.  At higher cones it's quickly gone.

     

    These commercial glazes are partially lead fluxed manganese glazes which form a green, blue or red glass, with a reflective layer of gold or silver on the surface.  The key to success with these glazes seems to be having a very smooth bisque surface and a thick application that often runs.  The Amaco Palladium has a tendency to pinhole on many clays which I've only seen in fluorine containing frits like Ferro 5301 and 3269. 

     

    I prefer the reliability of the ^05 gold glaze, which becomes especially gold when placed over a previously fired ^6 glaze to provide a smooth surface and protection against clay off-gassing.

     

    I thought the golds would be out of it pretty low on the firing scale, after which you get the colors written above.

  2. Metallic Rain, which I have not tried, is similar in chemistry to Spectrum Metallic Mirror and Amaco Palladium.

     

    Amaco says their leaded Palladium is not dinnerware safe, but Spectrum says leaded Metallic Mirror is food-safe based on the glassy non-leeching finish of the glaze  "Contains some heavy metals and/or cadmium compounds but passes test for lead and cadmium release.".

     

    You need a small amount of lead to create this type of look.  But they don't use enough lead to make these glazes reliable.

     

     

    I think you'd be far happier with a standard ^05 lead-manganese glaze like these sold by Clay Planet - very reliable, but not food safe.

     

    http://shop.clay-planet.com/pint-722-aztec-gold.aspx

     

    Has anyone tested Spectrum's new Metallic Gold Rain?  I would like to try it on a sculpture but need to pay shipping to test.  I assume it doesn't actually look like the promotional test tile- but I'm looking for something stunning!!

     

    Thanks!!

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