Iron oxide glaze John Britt

Here is a really nice cone 6 Iron red. And John said,"Don't have an image but trust me- it is nice! If you get an image - send it to me and I will post it."
114.3%    Magruder’s (Iron ) Red cone 6 oxidation
44.8%     Minspar (soda feldspar}
12.3%     Silica
18.2%     Talc
16.1%     Tri-Calcium Phosphate (45.76% P2O5 + 54.23% CaO) vs 42.39% / 55.82% for Bone Ash
4.3%     EPK 
4.3%     Lithium Carbonate
2.0%     Bentonite
12.3%     Synthetic Iron Oxide

NOTE: Replies are posted from oldest to newest, so the most recent posts will be at the bottom of the last page.
Test tiles on Laguna Haggi Porcelain (Norm Stuart)

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What is synthetic iron oxide?

Hi Barbara, I sent this info about synthetic iron back in Feb 2012 to Sylvia. It should explain things clearly if you check out John Brit's article in Ceramics Arts Daily. It is interesting to read.

Hope this helps.


Comment by Joan Scott on February 21, 2012 at 3:34pmDelete Comment

Hi Sylvia,

I had never heard of synthetic iron before either. It is described here in a pdf by John Britt  Very interesting article and another description here  and I am sure you can find other articles about iron. It really is interesting. And you must have read this article

You don't have any examples of your work. The one that is your photo is interesting but very small. How about uploading some pieces?


I have photos of four variations of Magruder Red below, all made with Kona F-4 and Red Iron Oxide Precipitate.

All are fired to cone 6 with a 50 degree F per hour cool between 1,800 F and 1,500 F.

The first is simply Magruder Red, compared with Orange Street also made with Red Iron Oxide Precipitate.

But wait, there's more!

Next is Kate Magruder Red with 10% Ferro Frit 3134 added.

Followed by Magruder Red with 10% Ferro Frit 5301 added. It has 9% Fluorine so has some crystallization in the very fluxed glass. Three coats on the left (top), one coat on the right-side (base).

Last is Magruder Red with Ilmenite added which changes it slightly but noticeably.

I never did Magriders by itself. When layered JM it variegated red and black but not very metallic. I like the variation with the 5301. I am liking more and more what 5301 can do. Maybe I should sub some into a crystalline glaze and see what happens.

I've found adding 16% Cryolite to 100% Ferro Frit 3269 is nearly identical to Ferro Frit 5301.

Adding 1.6% Cryolite adds the same level of fluorine that adding 10% of Ferro Frit 5301 provides and also bumps up the sodium.  But you're adding a little alumina and no silica.

Cryolite and 5201 are both interesting to play with because of the fluorine flux. For the same reason Lithium Fluoride (available at Laguna Clay) is far superior to Lithium Carbonate as a flux.

Interesting information. I have this for

Silica 15.2%
Talc 13.8%
Dolomite 8.1%
EPK 4.5%
Gerstly Borate 17.9%
F-4 Feldspar 46.8%
Red Iron Oxide 12%
Bone Ash 12%
Crocus Martis 6.2%

Is this the same as the one you pictured? Does your firing have any soak period etc.?

That's the glaze recipe we started with, but:

I substituted Yellow Iron Oxide for crocus martis which no longer exists, so is a different material depending on where you buy it.

I use a 99% pure synthetic red iron oxide called Bayferrox 110M, made using a Bayer Chemical patent. The primary market for this product is as a red pigment for paint, printers ink, plastics and concrete. Some ceramic suppliers like Standard Ceramic sell this red iron oxide as "precipitate" while others call it "special" or "synthetic" - and some suppliers like Laguna Clay/Axner don't sell it at all.

We use a pre-programmed Cone 6 firing built into our Bartlett V6-CF-700 controller, which is modified for Cress kilns, normally fired at medium speed. We hold for 30 minutes at the top temperature and use a slow cooling program between 1,800 F and 1,500 F of 50 F per hour, for a total of 6 hours.

Orange Street comes out very similar with faster cooling cycles with a little more gloss, just as it is glossier on iron heavy brown clay.

So my resulting glaze recipe is:

130.3%    ORANGE STREET  ^6
46.8%    Feldspar Kona F-4 or Minspar
17.9%    Gerstly Borate
15.2%    Silica
13.8%    Talc  (Pioneer 2882)
12.0%    Bone Ash
8.1%    Dolomite  (Dolowhite)
4.5%    EPK
12.0%    Red Iron Oxide Precipitate
6.2%    Yellow Iron Oxide

We have a copy of Michael Bailey's Cone 6 book somewhere at our studio, but I haven't read it yet. I will do.

As for tin, all of our most popular glazes have use tin oxide, and glazes with 7.5% or 10% tin oxide are far more popular than those with 2.5% or 5% tin oxide - it's the shine without the softness induced by sodium or potassium.  Tin oxide is expensive at $26 a pound which is not terrific. But I assume you're concerned about tin leeching from the glaze.

Inorganic tin compounds are basically safe in terms of leeching.

People who have eaten tinned food products which contain 200 mg of tin per kilogram of food have experienced nausea, vomiting and diarrhea - but this is a very high level of tin and the tin had probably recombined with the food over a long period of time into organic tin compounds which are toxic indeed. For this reason the UK food safety body set 200 mg/kg as the upper limit for inorganic food in tin.

All of the early toxicity problems with tin-plated food cans resulted from the lead solder used to seal the can. Some ceramic oxides and rutiles can contain a small amount of lead depending on their source. I always check the MSDS sheet (Materials Safety Disclosure Sheet).

This version of "Cream Breaking Rust" has 7.5% tin oxide. Really beautiful.
92.4%   Cream Breaking Rust  ^5 to 8
30.7%    Ferro Frit 3134
18.1%    Silica
13.0%    Tin Oxide  7.5
10.6%    Wollastonite
8.4%    EPK
6.0%    Red Iron Oxide - or  5%
3.3%    Strontium Carbonate
2.3%    Talc

Tin is very expensive to use but I have found that in some particular glazes and especially the quality in a glaze with iron oxide you can't achieve the rich surfaces with a substitute. I have tried but without success. What do you use instead of tin? 

Thanks for this. Do you have some of these slow cooling iron glazes in your photos? I would be interested to see them.

I see that Bayferrox link doesn't work, here is another.

It looks like Bayferrox 503 is the most pure red iron oxide.

98.1%  Fe2O3  1.3%  moisture,   0.6%  contaminants

Here's a few other Iron Red glazes most made with red iron oxide precipitate, except where noted. Not all of them are nice to look at.

Vee's Tenmoku Gold

The same Vee's Tenmoku made with Laguna very impure "Red Iron Oxide"

C. Harris Tenmoku

Reader's Digest Red

Floating Red (shown over Amaco Firebrick Red which uses Mason Stain)

Sankey Iron Red

the same Sankey Iron Red made with very impure and Laguna "Red Iron Oxide"


(shown after a bisque firing on the left, and a ^6 firing on the right)

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