clayart - thread 'red iron oxide'

Dr.Tom Roess on wed 2 aug 00

Hi everyone,
I have a quick question regarding Red iron oxide. We were recently given a nice quantity of the stuff but it was just labeled "red iron oxide". Does this mean it is 100% unless labeled 50%? Also, since most of our recipes have been based on using 50%, can we just use half as much and get approximately the same results?
I hope as many of you as possible will answer. I have noticed that when it is a matter of opinion, there will be many postings, but when it's a straightforward question, not too many people take the time to help out. I wonder why this is. =

Regards, Lou in Snowmass. =

Dennis E. Tobin on thu 3 aug 00

Lou,
First, say hi to Doug at the Ranch. He is an old friend from Mo. We started in clay at the same time, and back in '94 I was fortunate enough to have a two-month residence at the Ranch.

Regarding the iron, I have never encountered a substance labeled as "50% iron". What would constitute the remaining 50%? My supplier offers a light iron oxide and a dark iron oxide which might be similar. It's best to test the new product.
Good luck,
Dennis Tobin

Craig Martell on thu 3 aug 00

Lou inquired:
> We were recently given a nice quantity of the stuff but it was just labeled "red iron oxide". Does this mean it is 100% unless labeled 50%? Also, since most of our recipes have been based on using 50%, can we just use half as much and get approximately the same results?

Hi:

If the material is in the original packaging from the processor, check for the company name or other identifying numbers. If that's the case, contacting the manufacturer could provide insight into the material's strength.

The only definitive method to ascertain the percentage you'll be using involves conducting tests. You have the discretion to determine the number and methodology of those tests. However, I'd suggest starting with your original percentages and observing the results.

> I have noticed that when it is a matter of opinion, there will be many postings, but when it’s a straightforward question, not too many people take the time to help out. I wonder why this is.

I believe you're about to find out! :>)

later, Craig Martell in Oregon

Shelley Corwin on thu 3 aug 00

Lou, consider calling the Anderson Ranch; they should have some insights.

Ron Roy on thu 3 aug 00

Hi Lou,

In simple terms, you don't know what's in the bag, so it is prudent to perform a line blend in a glaze and determine its potency—start at 100% and scale down to 40%, decreasing 10% at a time.

As for your second question, I’ve observed the same trend. It's likely related to varying levels of technical awareness within the group; navigating through all the opinions to get to straightforward answers can be challenging. Nevertheless, we'll figure it out.

If you believe your question might be addressable by me or someone else on the list, consider adding our initials in the subject line; that tends to garner attention.

RR

Jim on thu 3 aug 00

Could someone shed light on the differences between the red iron oxide I use daily and "Spanish Red Iron Oxide"? Is one inherently redder than the other, or are there other distinctions?
Thanks, Jim in Dallas, where temperatures have cooled to 103 degrees.

Paul Lewing on thu 3 aug 00

Lou,
Without conducting tests, there’s no way to ascertain the contents of that bag. There exists a vast array of brands and strengths of iron oxide, processed through various methods, often with differing contaminants. Start by firing a test with the same amount you're accustomed to and adjust as necessary from there. The required adjustments won’t likely be significant, but if there are considerable proportions of other materials in either batch, the shade may vary.
The most frequent contaminant is probably manganese, which could mute the color and give it a browner hue. Generally speaking, the purer the iron oxide, the redder it will appear in its raw form.
Concerning your other question, it seems many might hesitate to respond to factual queries due to concerns about being inaccurate, whereas opinions lack right or wrong and are simply perspectives. Many on this list likely possess more knowledge than they realize, but they often await responses from those who have previously addressed factual questions.
Paul Lewing, Seattle,
who tends to sound knowledgeable, regardless of the truth.

iandol on fri 4 aug 00

Dear Dr. Tom,

Expressing opinions is simple, while establishing hard facts can be time-consuming and requires diligent searching. That’s my belief.

As for your iron oxide, unless you're dealing with a dishonest supplier diluting your product, it should be pure red iron oxide (Fe2O3). However, due to the inherent imperfection of natural materials, there may be other iron minerals present, though likely not in detectable quantities. If it’s raw and unrefined, it might also contain clay or common particles like fine sand.

What necessity would there be for a 50% value in a recipe? And if your label states 50%, what does the remaining 50% consist of?

Hope this helps,

Ivor Lewis

Tom Buck on fri 4 aug 00

Jim,
The archives hold insights on various types of red iron oxides. In previous discussions, it was indicated that Spanish red iron oxide comprises around 87% Fe2O3 and tends to have smaller particle sizes compared to synthetic variants. Alternatively, most synthetic red iron oxides possess a broader spectrum of particle sizes with a purity level of 90-95% Fe2O3.
Notably, Spain has extensive natural deposits of lower-grade Fe2O3 that undergo processing to reach high-grade purity; however, this process doesn’t eliminate all clay-like materials within the mineral ore. Synthetic variants are typically derived from scrap steel, potentially containing trace amounts of other metals (typically considered negligible) that potters receive.
Until next time, peace. Tom B.

Dr.Tom Roess on sat 5 aug 00

Thank you to Craig, Tom, Ivor, Ron, Paul, and Dennis for responding to my inquiry concerning Red Iron Oxide. (It seems to be our core group!) Dennis, I will indeed see Doug next week and extend your greetings.
I may have misled some readers regarding my reference to 50% RIO; I did not intend to imply a recipe required 59% red iron oxide. When I first began working at our studio, we had two containers of red iron oxide—one labeled 50% and the other labeled 100%. I was advised to utilize the 50% unless a recipe explicitly required a 100% or "pure" red iron oxide. It never crossed my mind to inquire what constituted the other 50% in the container.
The prevailing consensus is to experiment with the new product and ascertain its effectiveness. Thanks again, everyone,
Lou in Snowmass

Dapogny.Gail on mon 11 aug 03

Earlier this summer, as I was remixing a glaze (specifically orange), I was halted by the unexpected color of our guild's iron oxide. It appeared somewhat rosy and muted, distinctly different from what I recalled. Hesitant but committed, I proceeded to mix the glaze, anticipating an upcoming art fair.
To my surprise, the glaze emerged altered—no longer the familiar orange, but rather a gold shade. While acceptable, it was not my intended outcome.
Later, I consulted our archives for previous posts about iron. The insights were fascinating, albeit somewhat perplexing. Essentially, the older posts suggested that a better raw color of iron indicates greater purity and brightness. However, findings regarding Spanish Fe were mixed.
So, my question is: did that pinkish hue suggest I obtained a lesser quality strain? Should I seek out a redder variant? If necessary, could you recommend specific iron oxides and dependable suppliers?
Thank you—Gail

Gail Dapogny
Ann Arbor, Michigan

http://www.silverhawk.com/ex99/dapogny (single historical photo - no longer registered with Silverhawk)

Smith, Judy on thu 18 oct 07

I am facing challenges with red iron oxide. I combine it with a bit of water and apply it to my bisque ware. Next, I wipe off the excess. Upon drying, I then apply three coats of clear Coyote glaze and fire to cone 6. However, the result is that the iron oxide disappears underneath the clear glaze when I retrieve the pots from the kiln. What could be the cause? Should I consider skipping the rubbing-off step?

Thanks,
Judy Smith

Maggie Jones on thu 18 oct 07

Red iron oxide is particularly robust in its raw state, easily staining hands and garments but can weaken upon firing. It seems you may be removing too much or possibly using an excess of water. Achieving the right layering of particles is crucial to ensure visibility through any glaze.
Conversely, cobalt—especially in oxidized form—displays an inverse behavior, often becoming very pronounced in the firing, revealing areas that weren't visible on the unglazed piece.
Maggie

http://TurtleIslandPottery.com
Maggie and Freeman Jones

.........next OPEN Oct 27th Bring a friend!

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Fredrick Paget on thu 18 oct 07

> I am facing challenges with red iron oxide. I mix it with some water and apply it to my bisque ware. I then wipe off the excess. Once dry, I cover it with three layers of clear Coyote glaze and fire to cone 6. However, it seems that the iron oxide does not manifest beneath the clear glaze after removing the pots from the kiln. Am I doing something wrong? Should I skip the excess wiping step?
> Judy Smith

This situation echoes a similar problem we experienced with iron toner laser decals. The clear glaze appears to bleach the red iron oxide into a nearly colorless yellow.
Regrettably, I never found a clear glaze that does not yield this outcome.
Perhaps consider utilizing a mason stain rather than iron oxide, as it may not present this bleaching effect.
Fred Paget
--
Twin Dragon Studio
Mill Valley, CA, USA

Back from China with plenty of new ideas. I explored areas of China I had previously never visited.

Gayle Bair on thu 18 oct 07

My approach is to apply a very thin coat of clear glaze. I create an oxide-rich slip using red and black oxides, burnt umber, and a touch of black mason stain. This mixture only slightly fades when beneath a thick glaze layer.
Note that I generally do not wipe away excess, but rather use sgraffito techniques through the slip, preserving its thickness. However, I have created pieces where only red iron oxide was wiped away, and they maintained brightness under a diluted clear glaze, which I’d recommend applying in a thin manner—akin to skim milk consistency.
Gayle Bair
Bainbridge Island, WA
Tucson, AZ
http://claybair.com

-----Original Message-----
From: Fredrick Paget

> I am facing challenges with red iron oxide. I combine it with a bit of water and apply it to my bisque ware. Subsequently, I rub off the excess. Once dry, I apply three coats of clear Coyote glaze and fire to cone 6. Upon extracting the pieces from the kiln, the iron oxide seemingly fails to manifest beneath the clear glaze. Am I doing something incorrectly? Should I consider omitting the excess wiping step?
> Judy Smith

This scenario resembles a problem encountered with iron toner laser decals. The glaze tends to diminish the visibility of the red iron oxide, rendering it nearly colorless.
The quest for a clear glaze that does not produce this outcome has been ongoing without success.
Perhaps you might want to consider a mason stain as an alternative to iron oxide, as it seems to resist this bleaching effect.
Fred Paget
--
Twin Dragon Studio
Mill Valley, CA, USA

Back from China, overflowing with fresh ideas. I visited numerous unprecedented locations in China.

John Sankey on fri 19 oct 07

"I am experiencing difficulties with red iron oxide. I mix it with water and apply it to my bisque ware. After that, I rub off the excess and, once it has dried, cover it with three layers of clear Coyote glaze, firing at cone 6. However, upon retrieving the pots from the kiln, the iron oxide appears absent underneath the clear glaze...."

This is purely speculative, but I suspect that your red iron oxide (Fe2O3) undergoes conversion to FeO during the firing process. This, in turn, results in a light, transparent yellow hue when it interacts with the silica in your clear glaze. My experiences with iron glazes indicate that achieving a red hue from iron typically necessitates surface application.
http://sankey.ws/glazeiron.html

--
Include 'Byrd' in your subject line while replying to bypass my spam filter.

May Luk on sat 20 oct 07

Hello Judy;

Have you considered painting the iron oxide as 'an on-glaze' treatment, similar to the Maiolica process? Begin with glaze application, followed by painting your design using an iron oxide-water mixture. Experiment with different brush types for optimal results. I have employed this technique for Chinese calligraphy—particularly running script—without facing fading issues.

I'm certain you're aware that excessive coloring oxide may not be 'food safe.'

Best regards,
May
Kings County
My new kiln is in operation. Hooray!!

Snail Scott on mon 22 oct 07

Date: Thu, 18 Oct 10:10:25 -
From: "Smith, Judy"
Subject: red iron oxide

>...red iron oxide. I mix it with a bit of water and apply it onto my bisque ware. Then I rub off the excess. Once dried, I cover it with three coats of clear Coyote glaze and fire it to cone 6. The issue is that the iron oxide fails to show beneath the clear glaze....


Most clear glazes can ‘fade’ an iron oxide wash. Consider utilizing an engobe (or a similar commercial 'underglaze') of comparable hue if you wish the 'just-rubbed' appearance to remain unaltered. Moreover, a blend of multiple similarly colored engobes can yield a layered effect that appears richer than a singular application of one color.

Why are you glazing it? Is it necessary for functional reasons?

Personally, I prefer unglazed clay with any oxide wash; the contrast of glossy surfaces with an 'antiqued' effect rarely aligns well. Even if 'antique' isn’t the intent behind choosing an oxide wash, it commonly does not translate well when shiny.

-Snail
(I’m not overly fond of shininess.)