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Glaze formula suggestions


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https://www.facebook.com/1634468103/posts/10223056971406083/I have a glaze formula that I made myself. I have tried it in reduction, cone 7. It is a beautiful stony look, but has a very velvety feel. Does not seem to like my other glazes, as they pinhole over my new glaze. My new stoney velvet glaze crawls slightly where it settles in low places and gets thick. My question is, if I add some silica, say 3%-5%, will that stop the crawling? Here is the formula: Custer feldspar 40%, om4 ball clay 20%, epk10%, calcined epk 10%, Cornwall sub 13%, strontium 7%, ultrapax 5%, zinc 3%. Also added about 1/2% rutile and 1/2% manganese ox. 

I'm thinking maybe some silica will stop the crawling. Any suggestions will be greatly appreciated. :) Im having trouble posting a pic, but I'll keep trying

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Edited by Mudfish
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45 minutes ago, Mudfish said:

I'm thinking maybe some silica will stop the crawling

Don't think so, the silica level is already really quite high. Don't know if you use glaze calc software? If not I plunked your recipe into Insight. Have a look at both the alumina and silica levels, they are both higher than they need to be. Reduce  both the alumina and silica while keeping an eye on the silica to alumina ratio. If you want that stony matte finish keep the ratio approx the same. Your glaze isn't melting well with them both being so high. If this glaze is for functional work you might want to look at the R2O:RO flux ratio too. Work the recipe so you have approx the reverse amounts of what you currently have. Target would be 0.3:0.7 R2O:RO, but this isn't written in stone.

I don't have your analysis for the Cornwall substitute so I used Cornwall stone in the recipe.

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this is embarrassing, but I really do not understand glaze calc. I think you are saying that I should try reducing the alumina, (epk, om4), and reduce silica.. I'm thinking silica is from the custer feldspar. Then, after that, should I increase the flux? The  Cornwall sub is from Mid South Ceramics, but I don't have the formula. 

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1 hour ago, Mudfish said:

this is embarrassing, but I really do not understand glaze calc. I think you are saying that I should try reducing the alumina, (epk, om4), and reduce silica.. I'm thinking silica is from the custer feldspar. Then, after that, should I increase the flux? The  Cornwall sub is from Mid South Ceramics, but I don't have the formula. 

Nothing embarrassing about not really understanding glaze calc, we all started that way.

The clay content of the glaze is going to be supplying alumina and silica for the most part (and some other things), having 40% clay in a glaze is a lot. Custer is approx 70% silica so you are right on that point too. 

Don't know the reason you chose using strontium and zinc as fluxes? Zinc because there is no boron? If so you will need to increase that or add some boron. Strontium because...? With glaze chem the fluxes are looked at in a Unity Molecular Formula (UMF), they always total 1 therefore the alumina and silica are in relation to that. 

It's going to take some major surgery and testing this recipe to alter it enough to melt properly and adjust the flux ratio. Do you want to put the time into it or perhaps try an easier one? 

This recipe on Glazy looks promising, it's a calcium matte and also has a good silica to alumina ratio so there are two mechanisms creating the matte glaze. At the bottom of that linked page from Glazy and have a look at the analysis part. (screenshot just below also) Look at the silica level, alumina level and boron and compare them with your formula in the screenshot above. Then take a look at the silica to alumina ratio and the flux ratio and compare to your formula above. See how high your alumina and silica are in comparison? What I don't like about the Glazy recipe is how much epk is in it. I redid the recipe using part calcined kaolin and part epk, this will help avoid glaze crawling ( recipe at the bottom of this post, just round off to the tenth decimal place if you try a test amount)

If you want to adjust your recipe play around with it on Glazy (it's free) and change one material at a time and see what happens to the UMF. 

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One other consideration, this is a cone 6 recipe, probably okay at cone 7 but if not then reduce the frit a few percentage. (line blend would be fast).

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oh wow, thank you so much! I will try this and also I'm looking at Rat City Studio glaze formulas. What do you think of this formula? 

Dragon + 2% Nickel Carbonate

Recipe:
Minspar 44
Cornwall Stone 22
Whiting 18
EPK 5
Zinc 7
Titanium Dioxide 4
Bentonite 2

+2% Nickel CarbonateDragon + 2% Nickel Carbonate

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I've found that photos on glazy or other websites sometimes are not the actual result. Also, will the Katz-Burke formula work well on stoneware? I usually use a buff to gray/brown stoneware

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Might be a little low on silica which means it could have durability issues. Silica:alumina ratio is pointing more glossy than the Katz-Burke one but it has nickel which is refractory so might be about the same dryness/matte level. It always takes testing, looking at a formula or recipe will only get you so far, a glaze can look okay in theory but firing and testing a sample is the best test. Glaze calc gets you in the ballpark and is good for adjusting recipes, ruling out glazes that aren't going to be durable, predicting gloss level, looking at the flux ratios and LOI but you still need to fire a glaze test.

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