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subject: crystal formation in glazes

updated sun 13 nov 11


Joseph Herbert on fri 11 nov 11

Linda Stauffer wrote: "It was a huge hexagonal crystal, about 1.5" across
and an inch thick."

Actually, a huge hexagonal crystal would be 6 feet across and 30 feet long.
Composed of Beryl, the stuff dreams are made of. Probably not what you
have, but some such examples have existed, just not in glazes.

To start identifying, it must be water soluble (unless a student is salting
your glaze slurry) and a common glaze constituent. There are not so many
things it could be.

How hard it the crystal? Can you scratch the surface with your fingernail,
with a penny, with your teeth, with a knife, with that stone in the ring he
claimed was from Kay's?

How heavy is the crystal? Does it seem lighter than a normal rock for its

Will it disolve in water?

In a shino glaze one would suspect some form of sodium carbonate (washing

Also, Hexagonal has a rather specific meaning in the crystal world. Things
can show six sides, with various inclined angles and not be actually
hexagonal, in the crystal class sense.

If you heat it up and it turns to white powder that will dissolve in water
and raise its pH, sodium carbonate becomes more and more likely.

Good luck with that...