Same high-iron glaze. One crystallizes and the other does not. Why?


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 right, 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 left. 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 exact temperature 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, A cone 10R iron crystal glaze using only Ravenscrag Slip and Iron, Crystallization, Glaze Chemistry, Melt Fluidity


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