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GRNTCG - GRANITE Crystalline Glaze

Modified: 2022-10-13 21:48:58

Cone 8-10 - High titanium variant

Material Amount
Ferro Frit 311048.00
Zinc Oxide22.00
Silica20.00
Titanium Dioxide10.00
100.00

Notes

From Crystal Glazes Book 1 by Fara Shimbo, page 134.

Maturing Cone: 8 to 10 but is at its best at cone 9.
Crystal number: Moderate amount of zinc silicate crystals, but will also produce a very large number of titanium and/or rutile crystals
Rate Of Growth: For zinc silicate crystals, 1-2 cm diameter per hour on tiles, 1 cm/h on vessels
Crystal Color: Eggshell to light yellow, opaque.
Crystal Shape: Round with lighter edges; little structure visible.
Ground Color: Ecru to white, opaque in oxidation, mauve to purple in reduction.
Crazing: Impossible to see.
Color Response: Tends to dull colors somewhat. Crystals in copper glazes will often have maroon outlines. Takes all colorants well except nickel, which should not be used. Cobalt will color the rutile crystals a peacock blue; other colorants do not affect the rutile crystals much.
Seeding properties: Lousy.

More information in Crystal Glazes book 1 page 134. Much more background information in other sections of the book.

Related Information

Granite crystal glaze

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This glaze is great when you just need a change from what you’ve been doing. The bowl at right was done with the base glaze, reduced. No colorants were added, so I was quite surprised when this purple came out. It seems to come out very regularly when un-tinted titanium is used.
Adding colorants seems to destroy this purple. When I added rutile to the Granite base, I got a brilliant orange. Reducing this orange color gave me a slightly less-pinkish, more “burnt orange” color, that I quite like. There is no tinge of purple at all, which I suppose is just as well.
I have had success firing this glaze as low as cone 7, but the size of the zinc silicate crystals you can grow in the glaze seems to be directly related to the temperature at which this glaze is fired: the higher the cone, the larger the crystals. I suspect this is true of crystal glazes in general, but I’m only quite sure of it in this one.

Links

Firing Schedules Shimbo Crystal Schedule 1
Typecodes Crystalline Glaze Recipes Fara Shimbo
These are from Fara's Crystal Glazes books 1 and 2. Most are the frit 3110, zinc, silica base recipe (50:25:25) with small material additions at the expense of silica.
Recipes GBCG - Generic Base Crystalline Glaze
Cone 6-10 - Almost all other Frit 3110 recipes are based on additions to this

Mechanisms

Glaze ColorThe golden color of the rutile crystals shades all colorants added to this glaze toward the yellow. In light reduction, all crystals become decidedly golden and ground (in the absence of other colorants) becomes a pale mauve.
Glaze CrystallizationThis glaze produces both zinc silicate and rutile crystals. Zinc silcate crystals are patchy, but rutile crystals occur evenly spaced throughout the glaze surface (though they may be more visible where glaze is very thick).

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