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Thicken glaze?


ronfire
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I just mixed up a 40+ lb bag of plainsman G2926B clear cone 6 glaze. Mixed to a specific gravity of 1.44 as per directions for dipping.

I am adding Epson salt to thicken but it does not seam to have very little effect. I should have kept track of how much I added but  did not think of it at the time. My guess is I added about 1/2-3/4 kg looking at the container.

Does this seam excessive?  Is there a problem with adding a large amount of Epson salt to thicken? I am trying to get the glaze to a 2-5 second bounce back.

I just seams I am adding more than usual but have never measured the salt ( will from now on to keep track)

 

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Did you add it as dry material, or did you add it as a saturated solution? If that’s 1/2 kg dry in a 5 gallon bucket, yes that is definitely excessive! You will likely have a congealed mess when it all dissolves. If you can, screen it out!

Epsom salts will show their effect quickly when you’re using them already dissolved, but you need to stir the bucket thoroughly to incorporate before the effect is visible. 

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5 minutes ago, liambesaw said:

Not sure what the solution might be.

If he added it dry, it can take quite some time to dissolve, especially if the crystals are the big ones they sell as bath salts, and if you’ve used cold water to mix your glaze with. Sieve them out if possible and give the batch a thorough mix to see where you’re at. 
 

If it turns out the salts didn’t have a chance to dissolve and the glaze is quite thin or settles fast, you can take the material from the sieve (and probably more besides) and dissolve them in boiling water to make a saturated solution. You can then add that solution a few tablespoons at a time to your glaze batch, mixing thoroughly between additions so you don’t overdo it. 

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I use that glaze as a liner in my cast tumblers, I tried the saturated Epsom salts solution when I was testing it. It really didn’t do much in my test batch of 1 kg of glaze. I switched over to using 1% bentone ma (aka Macaloid), much better. I use it at a sg of 1.39, found 1.44 cracked while drying. Hope you can sieve most of that out Ron.

edit: fresh epsom salts solution made fixed the problem, it works.

Edited by Min
correction
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This glaze doesn't suspend well with epsom salts, I know it should as there is plenty of clay in it but from my experience with it it really doesn't.

edit: epsom salts worked in new test

Edited by Min
correction
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If you’re buying the whole dry bags from Plainsman, it comes in 20 kg measures. So no need to convert back and forth to Imperial. 20,000g at 1/2 a percent is 100g. 

Weird that you’re not finding the Epsom salts to work, @Min. I just mixed a 2kg batch of it last night, and the solution worked fine on it. I didn’t use the premix though: I just used my own raw materials. 

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1 minute ago, Min said:

This glaze doesn't suspend well with epsom salts, I know it should as there is plenty of clay in it but it really doesn't.

Probably from all the soluble sodium deflocculating it.

Also I believe talc can interfere with flocculation as well, but I don't remember where I read that.   Something to do with talc being unable to flocculate via cations unless in an acidic solution.

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38 minutes ago, liambesaw said:

Probably from all the soluble sodium deflocculating it.

Even when just mixed it doesn't want to suspend / thicken. 

I know Callie, it doesn't make sense but thats what it did. Same jar of epsom salts solution I always use. (I'm using my raw materials also, not the premix)  It's a nice glaze with the 1 bentone ma, behaves itself well.

Edited by Min
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I do have hard water but had no issues last time. I did add the salt in the crystal form and mixed it well and let it sit and mixed again. It sat overnight and is still thin. Just went out and ran all the glaze through a fine screen and had no  solids in it. The glaze temp now is at 62F and still not gelled. Not sure what to do at this point, might have to phone plainsman in the morning, wonder if they had a bad batch and missed something .

What happens to the salt when fired? Does it burn out?

Went out and did a better estimate and put in 300-500grams.

 

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It's magnesium sulfate heptahydrate.  Decomposes into anhydrous magnesium sulfate, which melts at ~1100c.  Not sure if it ever decomposes into sulfur and magnesium, may have a strong ionic or covalent bond.  In other words it's probably not gonna be too bad as far as effect on your glaze, and if you want to remove it, simply set the bucket outdoors and let it get really cold.  The epsom salts will probably recrystallize to some extent and can be removed.  Just thought of that, with that much epsom salts it should be easy to recrystallize and remove.

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If I recrystallize the salt and remove it I still need to thicken the glaze.  When I went to thicken the glaze I had some crystallized salt that I added boiling water to and thought it should have been enough  after that I added the salt directly.  Have to use this glaze in a few days and not sure what to do at this point. It would be a 6 hour drive to get more glaze and start again.  I know the specific gravity was 1.44-1.45 when I mixed it as I checked both with a hydrometer and scale weight several times.

Think tomorrow I will pull out a couple of litres and add some dissolved salt and see what happens.

 

Edited by ronfire
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19 minutes ago, ronfire said:

If I recrystallize the salt and remove it I still need to thicken the glaze.  When I went to thicken the glaze I had some crystallized salt that I added boiling water to and thought it should have been enough  after that I added the salt directly.  Have to use this glaze in a few days and not sure what to do at this point. It would be a 6 hour drive to get more glaze and start again.  I know the specific gravity was 1.44-1.45 when I mixed it as I checked both with a hydrometer and scale weight several times.

Think tomorrow I will pull out a couple of litres and add some dissolved salt and see what happens.

 

Do you have bentonite or macloid or veegumT?  Or even CMC gum?  If so, you can remove a portion of mixed glaze and see if you can use one of those to thicken it.  I would abandon the idea of epsom for now.

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I fourth this but with only a 1000 gram batch. This glaze is nearly 1:1 dry glaze to water so for a 1000 gram batch of liquid glaze add 10 grams of bentonite. I’ld heat up a bit of the glaze in the microwave then add the Bentonite and mix it with a stick blender. Should be okay but I wouldn’t commit the full batch until you’ve mixed a test batch.

Edited by Min
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