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Babs

Scumming In Glazed Ware.

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Had to go to a new clay body, supplier mining and preparing at different location. I am experiencing scumming ,though not all the time , not on all pots, on a low fired alkaline glaze fired to C03. Seems worse when I fire fast. I do slow bisques. Any suggestions, any way to get rid of scum thus formed??

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Norm,

 

I think you are referring to Muriatic acid from somewhere like Home Depot.

I never heard of that solution, but it makes perfect sense.

Especially since you can't add barium carb. to a moist clay. Great solution but use muriatic acid with care. I had some in a leaking container that I didn't notice when I transported it home. It ate the carpet on the floor of my van. I use barium carb. in small percentages when I mix my terra cotta to prevent scumming

 

Marcia

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It comes out after a day or so? That's totally weird. Can you post larger pictures, please. Those are too small to tell what's happening. Is the glaze fully mature? Is it a matte glaze? Is it a food safe glaze? Commercial glaze or do yo mix your own? Does it  happen with all glazes, or just some, or just certain combinations?

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I get that a glaze will have issues after 1,000 years, but in a day? Perhaps properly matured was not the correct term. Properly formulated, maybe? Any glaze that has this issue needs work. I've run literally thousands of glaze test over the last 20 years and have never seen this. The clay is probably not the real problem here, it just made the problem visible. The new clay is being mixed with different water that may have more salts present. I would start with the barium fix Norm described above. Any after-firing fix seems like a band-and solution to me.

 

I love it when we get this interesting stuff here.

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Well I think it is  an immaturity and too much neglect..

a. I bumped up the kiln

b. I did not soak or slow towards  the end of firing

c. I depended on the kiln sitter alone and so the temp. would have been lower because of the fast firing??

This is the only glaze I have issues with.

I use it for textured work and this scum loves the crevices.

I live near the ocean, salt and air moisture high....

But prob sheer neglect on my part.

Haven't got the recipe near so can't give details at mo. but it is a boron fritted, neph syn. base.  Usually gives a deep clear turquoise.

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Yes it washes off but returns!! Have washed a bit with vinegar and is still clear after a day but need to sort this as cannot rush around galleries wiping my pots!!

Used this glaze for a long time but occasionally when I lose my attention it  bites me. Just trying to blame everything but me! Will prob. go with an additoin of ball clay to try stabilising it under wider firing conditions.

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Think this glaze has pretty soluble ingredients so I'll read up on the poss. of reducing this and see if I can figure a way of retaining the colour without this prob. May not be able to get away from the solubility at this temp but poss to extent of getting rid of this scumming..doesn't happen often so I am doing something.

It doesn't do this all the time!!

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