Tuesday, January 03, 2006

On Mason Stains

Did a little research on Mason stains during lunch today, which mainly involved going to the Mason Color web site and trying to identify clues to what happened last week during the raku firing.

The first realization was that the page showing the pinks and crimsons does not include the Tangerine or Lobster stains that seemed to work in the "Louden's Base". The Sunset stain, the one that lead us to using Mason stains in the first place, wasn't there either.

It turns out that there is a separate tab for Encapsulated Zirconium, Cadmium, and Selenium stains. Tangerine, Lobster, and Sunset all appear on this tab. Chemically, they are treated differently than the Dark Crimson, which is a chromium/tin stain.

I also found out that Cornwall Stone, which makes up twenty percent of the base glaze, fires light green in the right conditions. I now believe that the Dark Crimson mason stain turned transparent during firing, due to one of four possible causes:

  1. overfiring (unlikely, since the Dark Crimson stain can go up to 2000 degrees F, and the pyrometer read 1830 degrees max).
  2. the presence of zinc in the glaze, which chemically bound with the stain (unlikely, since I can't find any reports of Gerstley Borate and Cornwall Stone containing zinc)
  3. the amount of magnesium oxide in the glaze (about three percent) bound with the tin and chromium in the mason stain
  4. the reduction firing of the kiln somehow caused a chemical reaction that bound the tin and chromium of the Mason stain


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