I am seriously terrified by the use of alcohol as the combustible material for the raku process. I've posted a video and said as much before, but there's a reason for this post beyond just the use of alcohol as the combustible material and the lack of proper safety equipment (no safety goggles, shorts, Crocs). It's the explanation that appears at 0:58 in the video:
The hottest spots will color up first, so be ready to spray water on spots you want to color freeze. Torch the copper colored areas later and spray water when you hit the desired color [to] freeze it. If you mess up, you can always refire and try again!Ok, on some level I've understood that the reduction of the metal oxides is favorable at high temperatures (we discuss that in AP chemistry as it relates to thermodynamics and Gibbs free energy, and we show it in material science when we demonstrate the copper sheet), and I even knew that the process was reversible because of that demonstration. I never thought to apply that to raku, however.
The reduction in raku happens best with the first few pieces pulled from the kiln because they're the hottest ones. The cooler ones are on the verge of being too cool for the reduction to take place. That's shown in the rainbow of oxidation that appears at 2:47. The oxidation builds back as the piece cools until the glaze is cool enough to lock the color in and not allow any more oxygen into the metal/metal oxide system. There's a sweet spot of temperature above which reduction happens, below which the glaze is set and neither oxidation or reduction can happen, and during which oxidation can happen.
But I never thought to 'refire' the pieces using a torch (5:40)...or to use a spray bottle to quick cool the piece below that magic range and lock in the color (2:40)....or to display my raku pieces in a drained hot tube (6:47).
That's brilliant in its simplicity.
As we hear at 1:48, "it's almost like a science."
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