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Ravenscrag Slip really shines in its ability to produce a good floating blue glaze at cone 6, this is the GR6-M recipe. The speed of cooling in the kiln affects the fired appearance. The mug on the left was cooled faster, using our drop-and-soak PLC6DS firing schedule. The other one was slow-cooled using the C6DHSC schedule. The latter schedule is preferable for these because the G3914A black inherits a much smoother surface. Of course, the slow-cooled lighter blue could be darkened by adding a little cobalt.
Both mugs use the same cone 6 oxidation high-iron (9%), high-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.
Recipes |
GR6-M - Ravenscrag Cone 6 Floating Blue
Plainsman Cone 6 Ravenscrag Slip based version of the popular floating blue recipe. |
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Typecodes |
Floating Blue
A popular cone 6 glaze that employed Gerstley Borate, it was very troublesome to use and to fire. Much work has been done to create alternative recipes. |
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