Cindy in SD on thu 7 apr 05
We all have glazes that change colors when refired with the next bisque
load. I think they do this because it gives them such an excellent
opportunity to grow lots of crystals, but I am puzzled as to why I
cannot seem to get the same effect with slow cooling--even 50 F/hr
between 1900 and 1600 F. Anybody know why?
Thanks,
Cindy in SD
Wes Rolley on fri 15 apr 05
Cindy wrote:
> We all have glazes that change colors when refired with the next bisque
> load. I think they do this because it gives them such an excellent
> opportunity to grow lots of crystals, but I am puzzled as to why I
> cannot seem to get the same effect with slow cooling--even 50 F/hr
> between 1900 and 1600 F. Anybody know why?
Since no one responded, I will take a shot, since I do both some
refiring and (almost) always fire down from 1950 to 1550.
When you refire to bisque temperatures, the underlying glaze has no
significant degree of melt. The color change is primarily the result of
oxidation, not cyrstalization. The reoxidation that takes place happens
on the surface of the glaze. When you cool slowly, there is ample time
for oxidation to take place, but there is also a chance for
crystalization to take place throughout the structure of the glaze. It
does not happen just on the surface.
At lesat this is what makes sense to me.
--=20
"I find I have a great lot to learn =E2=80=93 or unlearn. I seem to know =
far too
much and this knowledge obscures the really significant facts, but I am
getting on." -- Charles Rennie Mackintosh
Wesley C. Rolley
17211 Quail Court
Morgan Hill, CA 95037
(408)778-3024
http://www.refpub.com/
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