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: crystal glazes going bad -- and bottles changing color

updated sat 24 aug 02


iandol on fri 23 aug 02

Dear Fara Shimbo,=20

It has always been my understanding that "Aventurine Glazes" achieved =
their qualities because of pervasive crystalline constituents which were =
thrown out of the vitreous solution during cooling. Delay in cooling =
allows early seed crystals to develop and grow before there is a general =
nucleation throughout the mass of the glaze. Hence, I would suggest that =
you need to slow down the cooling rate of your kiln as a way of =
encouraging larger crystals.

As to why your bottles of prepared glaze are throwing down some sort of =
coloured precipitate is a bit of a puzzle. To be certain I would like to =
know about their compositions. One thing which could occur if you are =
using raw Sodium Silicate solution as part of the recipe of your crystal =
glazes is that you are getting a Silica Crystal Garden growing. Someone =
else may care to explain this phenomenon, but it can happen if copper =
sulphate and other soluble salts are mixed in with sodium silicate and =
some other odds and ends such as nails and bits of metal are thrown =
into the soup. Even though some things may be sparingly soluble it is =
possible to get crystals growing. At a nearby copper mine I saw where =
wrecked automobiles were being pushed into small salt ponds. The iron =
slowly reacted, but instead of being replaced by red rust, it was =
replaced by red elemental native copper powder. This was collect and =
sent to the refiners at a tidy profit for almost no work at all.

The Sun can supply energy to fund chemical reactions.

Yes, an interesting puzzle.

Best regards,

Ivor Lewis.=20