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Hi. I was looking for a nice white liner glaze and I came upon Turners White in a CAD article. It said it was good with cone 6 and cone 10 and mixes well with Mason stains. Sounds perfect to me,

 

The glaze called for soda ash which I was out of. I called my local pottery shop and he had Minspar 200 which he said should work well as a sub. 

So I tested it at Cone 6 and it came out very underfired looking. It was dry and cracked

This is the recipe I made

Dolomite 10

Whiting   9

Minespar 200 25

Custer Felspar 20

EPK 18

Talc   6

Silica 12

 

BEntonite   2

Zircopax     8   (I used Zircopax plus)

 

Is Minspar 200 a good Soda Felspar?
Could it have been Zircopax Plus instead of just Zircopax?
What can I do to fix this glaze for cone 6 firing.

Thanks

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I was looking for a nice white liner glaze

 

If your wanting a liner glaze then it needs to be specific to that clay body and not randomly going from cone 6 to cone 10. There is a lot of bad information out in the world. If your firing a cone 6 body to maturity you want a glaze that matures right along with it at cone 6(fully), not cone 7 or 10.

 

I dont have my recipes in front of me so I can't help there, but you definitely dont want to be putting a glaze that can "work" at 6 or 10 as your liner.

Min and Pres like this

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If it's good at cone 10, then it's underfired at cone 6. Rather than try fixing that one, take any good glossy cone 6 glaze recipe that you know works, and simply leave out the colorants and add 8-12% superpax/zircopax and you'll have a nice white glaze.

Min and Pres like this

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Thank you both and fair enough. My usual Base glaze is Hansen 20x5 and it works well for what I do. I have put Ziropax in and tested it and made a lovely white. I guess  I am feeling in a bit of a glaze rut and wanted to try something new.  

As for part of my question...

 

Does Minespar  200 work when a recipe calls for soda felspar?  

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Hi and welcome to these forums.

 

To answer your original questions, the reason it's rough and dry is that it is not melting enough at ^6. The reason it's not melting is because the ratio of fluxes (melty stuff) isn't enough compared to how much alumina is in the glaze. There needs to be a balance of fluxes to the amount of silica and alumina in the recipe. 

 

Also, I believe the original recipe had F-4 feldspar which is no longer available, not soda ash. F-4 feldspar is a soda feldspar, as is Minspar which is why the latter is being subbed for the F-4. Only a tiny bit of difference in the chemistry of these two feldspars that's why your supplier said it is okay to sub one for the other. Soda ash on the other hand is a very strong flux and if you had used 25% of that in your glaze you would have one heck of a melted mess to clean in your kiln.

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I did the same thing when I was glaze testing in New Zealand. I got a chalky result and just assumed it was from local material differences. Alas, I must say I am not entirely surprised to hear it didn't really work out.

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The glaze called for soda ash which I was out of. I called my local pottery shop and he had Minspar 200 which he said should work well as a sub.

Minspar has 12% KNaO and Soda Ash has 58.5% KNaO. If you swapped out exactly 25% for 25%; then you were way short on flux. A comparable substitution would have been Pearl Ash which is also 58.5% KNaO.

Nerd

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The glaze called for soda ash which I was out of. I called my local pottery shop and he had Minspar 200 which he said should work well as a sub.

Minspar has 12% KNaO and Soda Ash has 58.5% KNaO. If you swapped out exactly 25% for 25%; then you were way short on flux. A comparable substitution would have been Pearl Ash which is also 58.5% KNaO.

Nerd

 

 

Except the original glaze called for a soda spar. At the time the article came out Minspar wasn't available, F-4 was the commonly used soda spar in North America. https://ceramicartsdaily.org/wp-content/uploads//2010/09/eunumpluribus.pdf

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If you want to alter your white, try blending other opacifiers. Try a triaxial blend with your base, and tin, zircopax and titanium as your 3 "colourants." It can change the quality of your white, which can sometimes shake things up.

I have been using two opacifiers together for a few years now. It allows the glaze to be more gray white, creamy white, or plain white. At the same time, always remember that any liner or white glaze if highly effected by the clay body underneath. I have used some of my regular whites used on a hazelnut brown clay body on a white clay body, and they are so different, that I need to rethink the glazes for the white before running any more tests.

 

 

best,

Pres

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