Michael Banks on wed 21 oct 98
A geological/minerals approach to the question about yellow iron oxide may
help: The three commonly mined (and thus commercially sold), naturally
occurring iron oxides (red, yellow and black) consist of three different
minerals. They are:
Red - Hematite (Fe2O3) ~70% Iron
Yellow - Goethite (FeO.OH) ~80% Iron
Black - Magnetite (Fe3O4) ~72% Iron
The yellow oxide is thus a significantly stronger source of iron for glazes,
in theory. However, in the real world yellow ochre/oxide is often diluted
with lime and silica. So its actual iron content will vary from supplier to
supplier. TEST, TEST, TEST.
As a footnote: Some books list black iron oxide as FeO, which is roasted
iron oxide, which doesn't occur commonly in nature. This synthetic material,
if actually available, would be the most concentrated source of iron short
of using steel filings.
Michael Banks,
NZ
mjbanks@clear.net.nz
Rick Sherman on thu 22 oct 98
Michael is correct. It is important to test. Red, Heatite, is sometimes
called Crocus Martis. This is usually used to designate it in a very
pure form. Fe203 can be contaminated with other materials. In order to
get his special yellow, Otto Heino imported one ton of very pure red
iron from Spain. I belive it is mined in Morocco.
Rick Sherman
San Jose, CA USofA
sherman@ricochet.net
----------------------------Original message--------------------------
A geological/minerals approach to the question about yellow iron oxide
may help: The three commonly mined (and thus commercially sold),
naturallyoccurring iron oxides (red, yellow and black) consist of three
different minerals. They are:
Red - Hematite (Fe2O3) ~70% Iron
Yellow - Goethite (FeO.OH) ~80% Iron
Black - Magnetite (Fe3O4) ~72% Iron
The yellow oxide is thus a significantly stronger source of iron for
glazes, in theory. However, in the real world yellow ochre/oxide is
often diluted with lime and silica. So its actual iron content will
vary from supplier to supplier. TEST, TEST, TEST.
As a footnote: Some books list black iron oxide as FeO, which is
roasted iron oxide, which doesn't occur commonly in nature. This
synthetic material, if actually available, would be the most
concentrated source of iron short of using steel filings.
Michael Banks,
NZ
mjbanks@clear.net.nz
Bruce Girrell on wed 26 sep 07
So if ochre isn't yellow iron oxide, what is it?
Are you simply saying the equivalent of "rutile isn't titanium dioxide"? If
not, what distinction are you trying to make?
Bruce Girrell
Edouard Bastarache Inc. on wed 26 sep 07
Bruce,
check these out :
http://ceramic-materials.com/cermat//material/1714.html
http://ceramic-materials.com/cermat//material/1094.html
http://ceramic-materials.com/cermat//material/2370.html
Gis la revido,
(A la revoyure)
Edouard Bastarache
Spertesperantisto
Sorel-Tracy
Quebec
http://perso.orange.fr/smart2000/livres.htm
http://www.pshcanada.com/Toxicology.htm
http://www.ceramique.com/librairie/
http://www.flickr.com/photos/30058682@N00/
http://myblogsmesblogs.blogspot.com/
Richard Aerni on wed 26 sep 07
On Wed, 26 Sep 2007 13:48:58 -0400, Bruce Girrell
wrote:
>So if ochre isn't yellow iron oxide, what is it?
Bruce,
I'm assuming you're not playing devil's advocate here, and truly want an
answer...
I've assumed through my readings over the years that Yellow Ochre is a
naturally occurring clay containing yellow iron oxide.
Yellow iron oxide as sold to the pottery industry is a purified form of
iron...check out the digitalfire website if you want the techie explanation.
Hope this helps,
Richard Aerni
Rochester, NY
Mark Issenberg on wed 26 sep 07
I have ocher that was mined near here,, north Goergia,, they are still
mining it ,, its a nasty pit.. Is going to be filled up and will be a new exit off
I 75.. It was one of the stops on the mine tour with the Weinman Museum last
year.. Now that a fun trip.. Was able to dig and carry home rocks
Mark
************************************** See what's new at http://www.aol.com
John Britt on wed 26 sep 07
Bruce,
My limited understanding is that yellow ochre is clay with yellow iron in
it and yellow iron is hydrated iron oxide.
In actual practice, yellow iron is great for celadons as it doesn't speck.
Hope it helps,
John Britt
www.johnbrittpottery.com
Ivor and Olive Lewis on thu 27 sep 07
Not sure to whom you are speaking Bruce, but I will join in.
A word came into my mind as I read again Yellow Iron Oxide.
This stuff is Limonite, one of the Hydrated oxides of Iron. It has a =
formula of FeO(OH) nH2O, On the porcelain tile it will exhibit a Brown =
Streak. It is amorphous, density 3.6 - 4, Mohs hardness 5 - 5 1/2
Yellow ochre, weathered Limonite possibly contaminated with Clay, Lime =
and other pale weathered rocks.
Thank you Herr. Wehlte and Mr. Dana for your erudite descriptions.
Best regards,
Ivor
Bruce Girrell on thu 27 sep 07
Thanks to all who set me straight on this. I naively thought that the terms
were interchangeable. I don't use either of these ingredients in my glazes,
so I never really paid much attention to which was what.
Bruce "we learn, one thing at a time" Girrell
Fred on thu 27 sep 07
I believe that someone asked about substuting yellow iron oxide for ochre. Can it be
done and in what proportions?
---- Ivor and Olive Lewis wrote:
>Not sure to whom you are speaking Bruce, but I will join in.
>
>A word came into my mind as I read again Yellow Iron Oxide.
>
>This stuff is Limonite, one of the Hydrated oxides of Iron. It has a formula of FeO(OH) nH2O, On the porcelain tile it will exhibit a Brown Streak. It is amorphous, density 3.6 - 4, Mohs hardness 5 - 5 1/2
>
>Yellow ochre, weathered Limonite possibly contaminated with Clay, Lime and other pale weathered rocks.
>
>Thank you Herr. Wehlte and Mr. Dana for your erudite descriptions.
>
>Best regards,
>
>Ivor
>
>______________________________________________________________________________
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at melpots2@visi.com
Ivor and Olive Lewis on fri 28 sep 07
No doubt it could be done Fred.
All that is needed are some assays of the samples that have been used in =
the past and those that are to be substituted in the future. Then it is =
just a matter of using a little simple arithmetic.
The big unknown would be "n" in the Limonite formula.
Best regards,
Ivor
---- Original Message -----=20
From: Fred=20
To: Clayart=20
Cc: Ivor and Olive Lewis=20
Sent: Friday, 28 September 2007 1:01
Subject: Re: Yellow iron oxide/ochre
I believe that someone asked about substuting yellow iron oxide for =
ochre. Can it be=20
done and in what proportions?=20
---- Ivor and Olive Lewis wrote:
>Not sure to whom you are speaking Bruce, but I will join in.
>
>A word came into my mind as I read again Yellow Iron Oxide.
>
>This stuff is Limonite, one of the Hydrated oxides of Iron. It has a =
formula of FeO(OH) nH2O, On the porcelain tile it will exhibit a Brown =
Streak. It is amorphous, density 3.6 - 4, Mohs hardness 5 - 5 1/2
>
>Yellow ochre, weathered Limonite possibly contaminated with Clay, =
Lime and other pale weathered rocks.
>
>Thank you Herr. Wehlte and Mr. Dana for your erudite descriptions.
>
>Best regards,
>
>Ivor
>
=
>________________________________________________________________________=
______=20
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at =
melpots2@visi.com
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