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docweathers

red versus yellow iron oxide

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I would like to substitute some red iron oxide in glaze formulas that use yellow iron oxide, because I don't have any yellow, such as Hanna's fake ash. I've looked yellow iron oxide up on Insight and various places on the web. It seems to be just a less concentrated form of iron oxide, but I don't quite believe it. Has anyone had any experience making this substitution? What has been your experience?

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our guild has used the same glaze for many years. the recipe is an attempt to copy old, 19th century stoneware that was made in our area. i is made with red iron oxide and i have made it with spanish red iron oxide twice and made it with yellow iron oxide once. that was just to try out yellow. nobody saw any difference in the fired results.

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If you are using a synthetic RIO with a Fe2O3 content of approx 95% and subbing it for YIO @ approx 88% wouldn't you just adjust your recipe accordingly? Gram for gram the yellow contains 7% less iron. I don't think the difference would be of any significance in glazes with moderate amounts of iron. My guess is that in glazes containing very large amounts of YIO you might get more pinholes from the high LOI that yellow iron has.

 

I use a glaze where I swapped the other way around, my base glaze has a lot of red iron in it and I spray a second iron glaze on top of it, subbing the yellow iron in the 2nd glaze makes it possible to see the 2 glazes during application.

 

Min

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That makes good sense and I will follow your advice.

 

Since I had seen some recipes from very advanced potters using both red and yellow iron oxides in the same glazes, I was just worried that I was missing something.

 

Larry

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You'll generally find very little difference between iron oxides when used in glazes. Domestic red iron oxide may be as low as 60% iron, same with yellow. Spanish iron oxide is only about 81%. Without knowing the actual iron content, I wouldn't worry about doing any math, just use the same amount.

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