From the Clayart archives:
(Also found in John Britt's High Fire Glazes, p. 68)
Tom Buck on fri 1 sep 06
I assume you are firing to Cone 10 and in reduction part of the time, otherwise you would not be quoting from John Britt's book, one of the few places where my original Celadon glaze is cited.
I mostly do Cone 6 oxidation (+raku) these days but I did design the Celadon blue for Cone 10 with light or zero reduction. Black iron oxide (FeO) is a very stable compound in a Cone 10 firing but it will act
as a "flux oxide" and if present above a minimal level it will melt alumina and silica. Which is why so little black oxide is used in a celadon; half (maybe) acts as flux, half as colourant.
If you have spanish red iron oxide, be aware that it contains 83-87% by weight of Fe2O3 (iron oxide red) and so that lower Fe2O3 content has to be considered when you replace Black Iron Oxide, FeO, which is high grade probably close to 100% by weight. Also, if your yellow iron oxide is pigment grade (and not yellow ochre which contains some clayey material then it too is high grade close to 100% Fe2O3.H2O or hydrated red iron oxide.
So, try my recipe and use Yellow Iron Oxide (pigment grade) in place of the 1% by weight of Black Iron Oxide (FeO). If you wish to be precise, add 1.13% yellow oxide and you will get 1% FeO when reaching higher cones. The success of this glaze depends on your claybody and how you fire the ware.
If you have spanish red, 1.18% will equal 1% black oxide.
Celadon colours are "solution" colours, that is, the iron oxide will actually dissolve (as opposed to dispersion or suspension) in the Liquidus (molten glaze), and when cooled, the widely located iron oxide (FeO) molecules will reflect incident white light in green or blue wavelengths.
may your tests go well. peace Tom B.
From another thread in Clayart, Mike Gordon lists the recipe with Wollastonite rather than Whiting:
Mike Gordon on mon 28 mar 11
TOM BUCK CELADON Cone 10
Custer Feldspar 30.00
Grolleg Kaolin 21.00
Black Iron Oxide 1.00
From yet another thread, Tom seems to indicate that his celadon recipe does in fact use Wollastonite.
Tom Buck on sun 21 jan 01
Perhaps you do not need this now. But I was doing some writing in Nov and had to put off some things. The basic problem with the Pinnell CB is WHITING, and 20 units is a lot of CO2 coming above 1800 F/1000 C. BTW Whiting is 44% CO2 and 56% CaO. You need a good soak to heal the burst bubbles, and where the glaze is thin healing may not occur even then.
The solution is to replace the Whiting with Wollastonite (CaO.SiO2) and when you do this the Silica/Flint needs changing too. here is how it comes out
30 Custer fs
additives as before.
Molecularly, the two recipes provide the same amounts of fluxes and glass-formers. It still will be glossy and with the same expansion/contraction.
til later. Peace. Tom B.
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