The same glaze fires very differently depending on kiln cooling rate

Wednesday 25th July 2012

Both mugs use the same cone 6 oxidation high-iron (9%), high-insight-live.com/glossary/129">boron, fluid melt glaze. Iron silicate crystals have completely invaded the surface of the one on the left, turning the gloss surface into a yellowy matte. Why? Multiple factors. This glaze does not contain enough iron to guarantee crystallization on cooling. When cooled quickly it fires the ultragloss near-black on the right. As cooling is slowed at some point the iron will begin to precipitate as small scattered golden crystals (sometimes called Teadust or Sparkles). As cooling slows further the number and size of these increases. Their maximum saturation is achieved on the discovery, usually by accident, of the likely narrow temperature range they form at (normally hundreds of degrees below the firing cone). Potters seek this type of glaze but industry avoids it because of difficulties with consistency.

Pages that reference this post in the Digitalfire Reference Library:

B2O3, Fe2O3, Same glaze fires hyper-matte and very glossy at cone 10. How?, Ravenscrag floating blue color affected by cooling rate, The appearance of this commercial glaze varies with cooling rate, The matteness of this glaze depends on the cooling rate, Cooling rate drastically affects the appearance of this glaze, Alberta Slip GA6-A glaze slow-cooled goes matte, Plainsman Cone 6 Drop-and-hold, Slow Cool, Glaze Chemistry, Crystallization

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