James Shepard on sat 14 apr 01
I have been under the impression that yellow ocher and yellow iron oxide was
and are the same thing. It has been recently brought to my attention that
this is not correct and the results as a colorant in a glaze can be
dramatically different depending on which of the two materials are used.
I've tried looking this up in catalogs, and have found very little
information. I would like to hear from the group about this.
Tom Buck on sun 15 apr 01
JS:
Ochre/ocher is a family of natural minerals, all some form of
hydrated iron oxide mixed with clays (ballclay types). The clay and other
trace minerals in the ochre make the behaviour of this material quite
different from iron oxides, natural or synthetic (eg Spanish red, iron
oxide red, Fe2O3).
Iron oxide yellow is hydrated iron oxide, usually written as
Fe2O3.H2O and is produced synthetically by recovering the iron oxide as a
precipitate from a solution of an iron salt. The yellow oxide has very
fine particles compared to yellow ochre, and it thus provides a stronger
colour effect, gram for gram.
Til later. Peace. Tom B.
Tom Buck ) tel: 905-389-2339
(westend Lake Ontario, province of Ontario, Canada).
mailing address: 373 East 43rd Street,
Hamilton ON L8T 3E1 Canada
Matt MacIntire on sun 15 apr 01
When in doubt... turn to the Internet for information.
here is an excellent page about yellow ochre:
http://www.sewanee.edu/chem/Chem&Art/Detail_Pages/Pigments/Yellow_ochre
Below is the portion of that page most relevant to your needs:
"Yellow Ochre is composed of hydrated iron oxide with a range of mineral
impurities, often humus and iron sulfate compounds. The chemical structure
is Fe2O3. It normally has seventeen to twenty four percent iron oxide. It
also has significant amounts of alumina and silica."
As you have learned, this clearly would not be direct substitute for pure
yellow iron oxide.
good luck...
Matt
bivaletz ginny on sun 15 apr 01
james - i was wondering the same thing not too long
ago and found a wealth of information on this subject
in the archives. you can access them by clicking on
the address listed at the bottom of each post. go to
search by subject and type yellow ocher in the
appropriate blank spaces.
i don't have much personal experience with it
myself, but it seems others do. good luck
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