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AndreaB

Crystalline Glaze Recipies For Cone 8/9

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Morning all, I love the effect of crystal growth in glazes. I want to experiment making a glaze for electric kiln firing on stoneware to cone 8/9. Can anyone share a recipies?

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Hi Andrea

 

First off, there is no set formula for crystalline glaze because of the numerous variables. The clay body, zinc, silica, frit, and kiln all effect the final glaze formulation. The basic starting point is: 50% frit, 25% zinc, and 25% silica: then 3-5% glaze hardener, and 1-5% lithium carbonate pending peak firing temp. An example of a variable is zinc: which can be metallic zincite, french process from zinc ore or sphalerite, or american process from sphalerite: each reacts differently in the glaze. There are over five varieties of french process that could be used, and the same for american process zinc. The processing method and the purity level of each type of zinc all changes the amount needed in the glaze formula. So your basic 25% zinc could end up being 30%, or as low as 22%.

Two frits are used primarily: which are Ferro Frit 3110 and Fusion Frit 644: although others can be used. Move outside of the USA into Europe and Degussa frits are used. What is available in South Africa may also be different. The same variables apply to the zinc and silica: different sources have different purity levels. So you have to then look at the chemical analysis of each and align them with those that are proven in crystalline glaze.

I assume you are use to throwing stoneware clay; which is not compatible with crystalline glaze. You can however coat a thrown stoneware piece with a porcelain engobe or slip: whichever method you are use to. You can also use a 50/50 porcelain & stoneware body: but crystal development will be roughly half that of a pure porcelain body. Some porcelain bodies are more conducive to growing crystals than others because of the fluxes used. Sodium is a crystal killer, and potassium will certainly hinder crystal growth. Calcium is acceptable in low percentages.

Once you start firing this glaze, you then need to learn how to read the crystals. No, not in some  voodoo weirdness but in what they tell you in formation. Thin spike and needle crystals tell you that you have too much sodium and potassium in one of your ingredients. Thick spike and needle crystals tell you the glaze is okay, but the soak temp needs adjusted. If you want to dive in I will certainly coach you along: but crystalline glaze takes some time to master. I have worked with this glaze almost excursively for the past 5-6 years and am just now comfortable with it. The reverse end of this equation: crystalline glazed pieces bring 3-5 times the money as standard glazes.

 

Nerd

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Hi Andrea

 

First off, there is no set formula for crystalline glaze because of the numerous variables. The clay body, zinc, silica, frit, and kiln all effect the final glaze formulation. The basic starting point is: 50% frit, 25% zinc, and 25% silica: then 3-5% glaze hardener, and 1-5% lithium carbonate pending peak firing temp. An example of a variable is zinc: which can be metallic zincite, french process from zinc ore or sphalerite, or american process from sphalerite: each reacts differently in the glaze. There are over five varieties of french process that could be used, and the same for american process zinc. The processing method and the purity level of each type of zinc all changes the amount needed in the glaze formula. So your basic 25% zinc could end up being 30%, or as low as 22%.

Two frits are used primarily: which are Ferro Frit 3110 and Fusoin Frit 644: although others can be used. Move outside of the USA into Europe and Degussa frits are used. What is available in South Africa may also be different. The same variables apply to the zinc and silica: different sources have different purity levels. So you have to then look at the chemical analysis of each and align them with those that are proven in crystalline glaze.

I assume you are use to throwing stoneware clay; which is not compatible with crystalline glaze. You can however coat a thrown stoneware piece with a porcelain engobe or slip: whichever method you are use to. You can also use a 50/50 porcelain & stoneware body: but crystal development will be roughly half that of a pure porcelain body. Some porcelain bodies are more conducive to growing crystals than others because of the fluxes used. Sodium is a crystal killer, and potassium will certainly hinder crystal growth. Calcium is acceptable in low percentages.

Once you start firing this glaze, you then need to learn how to read the crystals. No, not in some  voodoo weirdness but in what they tell you in formation. Thin spike and needle crystals tell you that you have too much sodium and potassium in one of your ingredients. Thick spike and needle crystals tell you the glaze is okay, but the soak temp needs adjusted. If you want to dive in I will certainly coach you along: but crystalline glaze takes some time to master. I have worked with this glaze almost excursively for the past 5-6 years and am just now comfortable with it. The reverse end of this equation: crystalline glazed pieces bring 3-5 times the money as standard glazes.

 

Nerd

All I can say is WOW, here I am a newbie to ceramics thinking I could just whip up some ingredients and voila I have a Black Forest cake. To say I admire your chemistry is nothing short of an understatement. Thank you for your very detailed reply, I think I'm going to go very small with my first glazes.

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Morning all, I love the effect of crystal growth in glazes. I want to experiment making a glaze for electric kiln firing on stoneware to cone 8/9. Can anyone share a recipies?

Here is a base recipe that works at cone 8 down to cone 9 -15%.  You will have to experiment with colorants. The 3 hour soak range is from 2000 Deg F to 1980 deg F. Allthough porcelain may be the preferred clay I use my stoneware clay and am pleased with the results.  The size and amount of crystals vary with vertical or horizontal surfaces.

Frit 3110                  53.6

Calcined zinc Oxide 26.7

Silica                        19.7

David

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Hi David:

You are one of a few who use stoneware for crystalline glaze. Susan Bunzl of Germany uses it sometimes; but also uses porcelain. Kate Malone in the UK uses Morganite T4 structural clay: but she does some heavy sculpted pieces. Ayca Riedinger of Germany primarily use a 50/50 blend and Peter Frohlich of Austria is the only one I have known up to this point who uses stoneware only. I must say that Frohlichs work is exceptional and his crystal formations on stoneware are every bit as good as any I have seen on porcelain. I think Bill Campbell of the USA has used stoneware on some of his sculpted pieces, but I am not sure. Most of the crystalliers in the USA that I know use porcelain, or a 50/50 blend on heavier pieces. I do know that the potters in Germany, Austria, and two in Belgium all use a stoneware body from Fuchs company in Germany, Would be interested to see some of your pieces on stoneware. Early on I tried this glaze on two different stoneware bodies with dismal results. I have since changed my recipe several times: perhaps I should give it another shot.

Nerd

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Morning all, I love the effect of crystal growth in glazes. I want to experiment making a glaze for electric kiln firing on stoneware to cone 8/9. Can anyone share a recipies?

 

Here is a base recipe that works at cone 8 down to cone 9 -15%.  You will have to experiment with colorants. The 3 hour soak range is from 2000 Deg F to 1980 deg F. Allthough porcelain may be the preferred clay I use my stoneware clay and am pleased with the results.  The size and amount of crystals vary with vertical or horizontal surfaces.

Frit 3110                  53.6

Calcined zinc Oxide 26.7

Silica                        19.7

David

Thanks David, I'll certainly try this

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Dave:

Ty you for sharing pictures of your work with me: very impressive crystal formation/work. Took a look at the stoneware body: no grog, fine silica mesh, added iron and low sodium fluxes. Unusual for a stoneware body, but these factors certainly change its reaction to this glaze. Enjoyed viewing!

Nerd

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