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FO - Octal Crystalline Glaze

Modified: 2022-10-13 21:48:15

Cone 6-9 - Fast-growing crystals variant with dolomite and spodumene

Notes

From Crystal Glazes Book 1 by Fara Shimbo, page 143.

A general-purpose crystalline glaze meant to grow crystals quickly and mature at a lower temperature than most. This glaze will mature as low as cone 6 and works well with all colorants.

Maturing Cone: 6-9, 10 if you really want it but may not produce as many crystals as at cone 9. At its best at cone 8. Fired to cone 5, it does not form crystals unless seeded.
Crystal number: Moderate.
Rate Of Growth: 1 cm diameter per hour, slightly more on tiles.
Crystal Color: Very White, translucent to opaque. Sometimes bluish.
Crystal Shape: Will flare out when held at a low temperature during a soak. Often has
"pointed" centers, as if one is looking at a volcano from above.
Ground Color: Colorless transparent to ever so vaguely translucent on both tiles and vessels.
Crazing: Varies with crystal growth (more crystals, more crazing), but not too much unless applied very thick. Then crazes like fury.
Color Response: Works well with all colors. Copper in reduction so far has always given red or copper crystals on a turquoise ground.
Seeding properties: Fair with zincite but often grows so many crystals that your pattern may be lost on a tile.

Octal is a very forgiving glaze and produces great crystals over a wide range of maturing temperatures so long as the kiln’s rise to final temperature is fast. I find it better for most uses than Vesuvius (which follows), unless I want the particular crystals that Vesuvius produces.

Related Information

Octal crystal glaze with three colorants

A vase made from Zen porcelain, about 28 cm tall. Top glazed with Octal + 3% red iron oxide; middle with Octal + 5% manganese dioxide; bottom with Octal + 3% cobalt carbonate. Fired to cone 7, reduced for about three hours.

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