Mike Gordon on mon 28 mar 11
Janine Roubik:
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.
Tom Buck ) -- primary address.
"alias" or secondary address.
tel: 905-389-2339 (westend Lake Ontario, province of Ontario, Canada).
mailing address: 373 East 43rd Street, Hamilton ON L8T 3E1 Canada
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