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wood ash-synthetic ash-stuff

updated sat 20 feb 99


Craig Martell on fri 19 feb 99


I've been reading the pros and cons about washing woodash and what this
process does and what different preferences are etc. So, for what it's
worth, I'll send in my uptake on the subject.

As most of you know already, soluble alkalai can be a very troublesome
problem with unwashed woodash unless you use all of the mixed glaze quickly.
If some folks have problems with solubles from Gerstley Borate, try unwashed
ash and you may then think that GB is almost trouble free. Solubles can
also cause problems in the clay-glaze interface, being carried into the body
of the pot by water transport. This doesn't happen all the time, but it's a

I wash my ash. I wash ash three times over a period of about two weeks.
This takes out enough of the solubles to eliminate glaze flocculation and I
can then store the glaze for long periods without problems. I don't much
care about losing soluble sodium and potassium because this is readily
available in insoluble form, via feldspars. What I want out of the ash is
calcium and phosphorous in whatever unknown proportion that it occurs. I
can get the calcium up to the point that it causes running and beading by
additions of whiting and or wollastonite if the amount of ash in the receipe
isn't supplying enough.

I've made some synthetic ash glazes by getting the calcium in the seger
formula up to the .85 to .90 range, which is a lot of calcium. The rest of
the flux is KNaO and MgO usually. These glazes are OK, but they don't
normally have the "sparkle" that one gets from using woodash. I think the
difference has to be "seen" and not ingested by reading or talking. Visuals
are the strongest avenue to understanding. I prefer to use actual wood ash
because it has it's own little secret life and unknown mix of oxides that
can't be forced and controlled by glaze calc and mathematics. I don't
expect to ever have total control of anything and I appreciate the unknown
gifts of natural minerals. Test, observe, and keep at it! Share with

Craig Martell in Oregon