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Underglazes Thinning On Their Own?


Benzine

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In my classroom, I've occasionally come across some of our commercial underglazes (Amaco), that seem very watery.

 

They seem fine, when the bottles are opened, but over time thin out.  I am not watering them down, and I've never seen a student do so either.  Most the time, if a glaze or underglaze is too thick, they bring it to my attention.  That's why I don't think they have had water added to them.

 

Is it possible that underglazes can thin out, due to a change in their chemistry?  They are not settling/ hard panning.  

 

Is there a solution/ fix to this?

 

On a somewhat related note, some turn darker in the bottle, regardless of color, and create a lovely smell.  The darkness burns out.  I'm guess this is due to a bacteria or mold eating some of the materials in the underglaze.  

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I have some arrive extremely watery. Most thicken over time, most likely due to evaporation even in the containers.

I have some that darken and smell, white especially will do this and yes it burns out and turns bright white in the kiln. Have read you can add a drop or two of bleach to fix the issue but I don't since the smell of beach bothers me more.

 

T

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I agree that the organic binders/extenders are diminishing. Typically they put a biocide in there to preserve them, but if they are especially old it can wear out. Add some gum solution with a touch of copper carb in it to preserve it. I usually make gum solution 2 tbsp bum to a gallon of water, plus 1/8 teaspoon copper carb.

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Is it possible that when some of the students who open a bottle a find it very thick and they do add water, and maybe a little too much, and these are the ones you didn't see do it and don't tell you?

 

They are high school students, so that is definitely possible.  After all, they know better than anybody, right?...

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Has anyone mentioned the possibility that these might be deflocculating?

 

 

If this was the case, wouldn't there be settling on the bottom?  There isn't any separation, just thinning.

 

I guess you'd have to check with slip casters, who routinely deflocculate their slips.  When I was a young potter, I designed a form to be cast, made molds, learned to work with slip. I don't remember that deflocculated slip settled out, but it was a very long time ago.

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This is an interesting subject for me.  I personally use a considerable amount of V-361 Jet Black.  However I had found that working it with an 18-gauge applicators I need to water it down to about a 1/3 strength.  However when I use it with a brush application I use it full strength.   However some of the other colors i will water down slightly for brushing, however I'll only dilute as much under glaze as needed for that day.

With students in a high school environment I ca n very easily see them watering down the glaze.  For there particular usage they might consider it to be excessively thick which is not an issue.  But instead of just pouring out what they need into a separate container and thinning it  they thin the entire batch.  Is it laziness to get another container?  Or is it that they cannot find another container with out searching for it?

Note it only takes a couple drops of water to thin out some of the under-glazes.

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As suggested, I added some gum solution. It thickened a bit after shaking for a few seconds. Checked a day later, and thickened even more.

 

We have another jar that is also getting thin. It also smells like rotten eggs. So I think Tyler's suggestion of the binder breaking down (with the help of some bacteria) is spot on.

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