Tom Buck on fri 22 jan 99
W. Hughes's Copper Blue was cited as a high Colemanite glaze, and because
this material is rare in N. America, there was request for a likely sub.
This mix barely falls within acceptable limits, and it would require far
too much Gerstley Borate to produce a good glaze on functional ware fired
to C02. So, one is left with using Borate frits to achieve the 0.9 moles
of B2O3 in the original mix. Here is a suggested revision:
27.0 Ferro frit 3211 (or equal)
13.0 Ferro frit 3195 (or equal)
4.5 Lithium carbonate
13.5 EPK (or equal)
42.0 Flint/silica
add 3.5% Copper carbonate (or equal in oxide).
This recipe raises the Silica content somewhat (10-15%), and so
the glaze may move into the acidic range which will yield a green hue
rather than blue that occurs when the mix goes alkaline.
Worth a test? BFN.
Tom Buck ) tel: 905-389-2339 & snailmail: 373 East 43rd
St. Hamilton ON L8T 3E1 Canada (westend Lake Ontario, province of Ontario,
Canada).
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