Janet H Walker on tue 17 sep 96
(Don't ask why but) I find myself with several pounds of Burnt Umber.
I can't find it listed in any of my catalogs or reference books so
I'm not sure how to calculate glazes using it. I remember seeing it
described somewhere as "ferruginous clay" so it's clay with (a lot
of?) iron in it. Can I just pretend for starting purposes that it
is like Barnard clay? or yellow ochre? Anybody have a bigger better
reference book than mine? TIA.
Jan Walker
Fun & Functional Arts
Cambridge MA USA
Richard Burkett on wed 18 sep 96
Jan,
I found this some time back, I'm sorry, but I don't remember where. It
should also be on the CeramisWeb Materials Database.
Burnt Umber
Equivalent Molecular Weight: 295.949
Molecular Formula of Burnt Umber:
CaO 0.180 Al2O3 0.180 SiO2 0.890
MgO 0.110 Fe2O3 1.000 MnO2 0.390
LOI 0.890
Percentage Analysis
18.06 % SiO2
6.20 % Al2O3
1.50 % MgO
3.41 % CaO
53.96 % Fe2O3
11.46 % MnO
5.42 % L.O.I.
______________
100 % TOTAL
Richard Burkett
richard.burkett@sdsu.edu
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