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Chris Throws Pots

Glasslike Crystals in Wet Glaze - What the...?

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After letting a big batch of my tin white liner glaze sit for about six week, I’ve just sieved it to start working with it again and found a pile of glass-like crystals sitting on my sieve’s  screen. My glaze has been stored in a cold area (it our most recent cold snap the temperature inside my storage space probably got down to high 40s/low 50s) but it hasn’t been exposed to freezing temperatures.  Some of the crystals look like snowflakes, while others are just chunks.  Does anybody know what they are and why they developed in my glaze?  My hope is that they are just debris, but my better sense tells me that they’re one of the glaze ingredients. 

Is it worth saving drying and weighing the crystals and then replacing an equivalent of the powdered ingredient into the wet glaze before using it?  Or can I just toss them and move on using the glaze as normal? 

594FE22F-6733-4FFA-AE4F-0089F5B91CA3.jpeg

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Thanks, Sputty, for sharing this! In my dismay at discovering the issue I didn't exercise the most patience, and jumped straight to posting a new thread, rather than searching through the resources already available. Per the linked thread, I believe it's the lithium carb that has crystallized due to inactivity and temperature drop.  I saved as many of the crystals as I could and will be microwaving them along with some of the now lithium-deficient glaze to get them back into solution.

Neil, the recipe is as follows in case you have any other theories or can confirm that lithium is the culprit.
Tin White Liner  ^6 Ox
Silica: 2.1
Custer: 64.4
Zinc Ox: 5.4
Gerstley: 14.5
Whiting: 3.0
Lithium Carb: 3.1
Tin Ox: 7.5
add
Bento: 2

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1 hour ago, Chris Throws Pots said:

I saved as many of the crystals as I could and will be microwaving them along with some of the now lithium-deficient glaze to get them back into solution.

Do report back if successful!

Edited by Sputty

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You can supply the lithium from a frit to (mostly) avoid getting the crystals if they get to be a nuisance. I played with your recipe over lunch, reduced the custer by over half to get some clay in the recipe, could leave the talc out altogether as it’s not going to be doing much. Sodium and potassium amounts are more or less reversed, supplied mostly from the custer and 3110. Other fluxes remain the same, as does the alumina and silica. Should behave better in the bucket and application, probably wouldn’t need to add bentonite. Expansion is tiny bit lower but still really high as it is in your recipe. (your recipe is glaze #1, my version of it is #2)

5a8b4ed468335_ScreenShot2018-02-19at2_20_59PM.png.0f874f2a86c1722a3405c5789d18eaeb.png

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Thanks so much, Min, for taking the time to run this exercise!

Per an older thread about possible composition abnormalities in custer, reducing the overall percentage of custer seems like a good idea... if I get a funky batch of custer the impact on the glaze would be more mild (in theory at least). Also, the price reduction is a nice bonus. Just need to find a retailer of Fusion frits.

I use iron laser decals in a lot of my work and have found that some of my ^6 glazes are not tolerant of the ^06ish decal firing.  Some glazes seem to begin fluxing in the decal firing, but without making all the way to ^6, so they are rendered soft, matte, scratchy, no longer food safe (using acid test). Will the chemical changes you've suggested alter either the stiffness of the glaze when fired to ^6 or lower the point where it begins to flux? Do you see any issue with this glaze begin brought back up to ^06ish? My iron decal program is 100/hr to 200 hold 0:30; 275/hr to 1810 hold 0:15.

Edited by Chris Throws Pots

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No problem Chris, I enjoy playing around with glaze calc,  it’s kind of like doing a crossword puzzle. 

My version is probably going to melt earlier than yours as I used some frit. Since frits have already been melted once they melt sooner in a glaze than supplying the same ingredients from raw materials. My version also might be a bit more fluid than yours because of the frits. You look at recipes on an oxide level (that little box in the lower right corner of my screenshot above), apart from the changes in sodium and potassium our formulas are the same.

I thought your original recipe was way too high in custer. If you have a recipe really high in custer then the alumina it’s supplying is going to be high also, that means there won’t be much room for clay in the recipe. If you don’t have any clay in the recipe there can be issues with slurry suspension in the bucket, settling and hard-panning, and drips when dipping. Also found it odd that on the one hand there is a high amount of sodium and potassium (makes for increasing expansion figures in a glaze) and then it looks like the lithium and zinc are in there to try and bring it back down a bit.

Are you totally committed to this glaze or are you open to another one? I’m hesitant to just pass along recipes since this one has a fairly high COE, if you are using it as a liner then I’m guessing your other glazes are high COE also? If you have another gloss recipe that you use on the outside of the pots you use this liner with we can have a look at the COE figure and see how they compare. Do you get any crazing with this glaze and any chance you have run crazing stress tests with it?

(BTW Fusion frits are available from Georgies on the west coast if you can’t find them by you)

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On 2/19/2018 at 3:36 PM, Sputty said:

Do report back if successful!

Happy to report that microwaving the lithium crystals did work to get them back into solution. I used a blender to chop them up, covered them in some of the lithium-deficient slurry and nuked them for 2 minutes, stirring after 1 minute. I was a little nervous that they'd recrystallize due to the rapid temperature drop when I sieved the mixture back into the bucket, but they seem to be fine. Thanks for all the help y'all!

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