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"There is a description of a high potash frit made from pearl ash, feldspar and kaolin in Michael Cardew's "Pioneer Pottery", page 144 to 148. He writes that it "breaks all the rules of frit making" and uses it to make a bright iron red glaze." Paul Herman

Pearl Ash Glazes Iron Red Cone 10 Bone Ash 2.91 Pearl Ash 10.68 Whiting 25.24 Custer 6.8 Grolleg 35.92 silica 18.45 Spanish Red 9.71

  • potash Frits Traxial alumina potasiumSilica phase diagram.

Potassium Siklicate from

Interesting K Frits 3191 Ferro 3185 Ferro

  • Wood ash, most wood anyways has soluble potassium and soluble sodium. Mostly what it has is soluble potassium. It has these along with calcium and and magnesium compounds. When the ash is fired hot and not burnt outside a kiln or furnace you end up with calcium hydroxide eventually and also magnesium hydroxide, this does not seem to be true at lower temperatures, you end up with either the carbonates or a mix (needs confirmation, my evidence is real thin here). The higher you heat the ash the more soda and potash volatilize and the less there is in the ash. If you heat hot enough some of this soluble soda or potash fuses with the ash and you end up with more insoluble alkali metals (soda and potash) along with the alkaline earth.

Consequently washing ash that was burnt in a kiln has less of an impact on how it melts when used in glazing because you wash out less soluble salts and more stays. (some of this is a bit more than conjecture but not quite tested well, yet.)

When looking at wood fired pots you see (at least) two kinds of ashing effects. One is the alkaline earth ash (caclia and magnesia). In the front of the kiln this sticks everywhere but as you go back it tends towards rims and places where particles can settle.

The other set of effects is the alkali metal effects. These look like soda and salt but are usually (it seems) more potash than soda.

I have sprayed calcium chloride into our soda kiln (just one port) and you can see the color change to look more like wood ash but it moves like a fume and not like larger particles so it spreads around the pot more like soda, but colors like calcia.

I have also done this with Espom Salts (magnesium sulphate). Like dipping pots in epsom salts you get a glaze surface that does not fit the pot and can shiver (have seen this) and perhaps dunt (have not seen this) the pot.

Potassium carbonate favors grey colors when fired as fusion buttons which confirms information that John Neely told me. Our tests down here in Texas with low temp processed bamboo ash so far confirm this too.

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Page last modified on January 31, 2018, at 12:28 AM