David W McDonald on tue 23 nov 99
Hi Chess,
Thanks for your mail. To answer your question, "You start
reduction on the way up at a much higher temp than the burst of reduction
on the way down. Any idea why this works?", yes, I do have some ideas. My
higher tempurature range of reduction on the way up takes care of the
needs of clay body reduction, and glaze reduction affecting the other
metalic oxides, but I believe it does not affect the copper reds insofar
as the red coloration. According to what I learned from the intensive
glazing and firing workshops I attended with Pete Pinell, the main reason
that copper red is so elusive is that the copper in the glaze turns red
at much lower tempuratures than what we are firing to in high temp
reduction firings. In my experience that range is around 1400 to 1500
degrees F. So if we are trying to reduce our copper reds at the same time
as the clay body and other metallic oxides in the glazes (cone 06 to cone
10), we are not giving the copper it's reduction at the tempurature it
desires for red formation. I've heard of many potters getting good reds
when they start reduction at cone 010 on the way up. For me though, I
just like the consistent results I've experienced getting by reducing on
the way down as I've described. Hope this helps. David McDonald
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