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Hannahs Blue Fake Ash Glaze

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I am new to the community.  My website is Eastwood Pottery

I have a question regarding Hannah's Fake Blue Ash glaze.  My glaze always comes out brown.  I left out the RIO and just used the Cobalt Oxide but I still for the life of me cannot get blue.  Does anyone out there have success using the blue ash glaze and do you use cobalt oxide as in the recipe?

 

 

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2 minutes ago, Eastwood Pottery said:

I am sure it was1.3. Tested twice. 

But are your sure that your cobalt is actually cobalt, and not some other material of similar raw color like manganese or a black stain? Have you used that cobalt to make blue in other glaze batches?

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11 minutes ago, Eastwood Pottery said:

I have not used it in anything else. It is labeled cobalt oxide.   One I worry the supplier messed up, and it wasn’t cheap. 

I would test it in a basic clear glaze and see what color you get. At 1.3% it should be blue.

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31 minutes ago, neilestrick said:

@Eastwood Pottery Are you sure your cobalt is cobalt? At 1.3% you should be getting a blue background for sure. Have you used the same cobalt in other glazes?

It doesn't look underfired to me. Plenty runny.

I'm no expert, and I would agree that it looks plenty runny, but some of the runny bits look "puffy" and more matte, like an underfired glaze.  I have zero experience with this glaze, just something that I noticed.

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Brown is almost always caused by iron in my experience.  Redart has a massive amount of iron in it.  This is probably completely overwhelming the much smaller amount of cobalt in the recipe.  Try substituting some other kaolin/clay for, say, half of the red art.

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18 minutes ago, curt said:

Brown is almost always caused by iron in my experience.  Redart has a massive amount of iron in it.  This is probably completely overwhelming the much smaller amount of cobalt in the recipe.  Try substituting some other kaolin/clay for, say, half of the red art.

Redart has about 7% iron, and by the time it's diluted with everything else in the recipe it's about 4.1%, which is not all that much. You can see a tile of that recipe HERE.

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4 minutes ago, neilestrick said:

Redart has about 7% iron, and by the time it's diluted with everything else in the recipe it's about 4.1%, which is not all that much. You can see a tile of that recipe HERE.

That's even on a red body

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The recipe in Neil’s link notes that they used a local red clay instead of redart. I would still recommend to OP to replace the redart with something lighter. 

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2 minutes ago, GEP said:

The recipe in Neil’s link notes that they used a local red clay instead of redart. I would still recommend to OP to replace the redart with something lighter. 

Even so, 4% iron isn't enough to wipe out 1.3% cobalt and turn it black with no hint of blue whatsoever.

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20 minutes ago, neilestrick said:

Even so, 4% iron isn't enough to wipe out 1.3% cobalt and turn it black with no hint of blue whatsoever.

I’ll take your word for it. I admittedly do not have much experience with blue glazes.

@Eastwood Pottery could you possibly have mis-measured the cobalt oxide? Oxide is super-concentrated, far more than cobalt carb. The oxide is often a component in black stains. A small measuring mistake can make a big difference. 

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My guess is that you are not using cobalt oxide;  probably manganese oxide; both materials are black powders.

Try this:  take a small white porcelain test tile, and mix a little bit of your "cobalt oxide" a little bit of baking soda in water and make  marks on the test tile.  Then fire normally.  If the marks are not a strong blue, your material is not cobalt oxide!.  

As a footnote, I always use cobalt carbonate rather than cobalt oxide because the carbonate form is cheaper per atom of cobalt AND cobalt carbonate is NOT black. 

LT
 

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