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Homemade Underglaze Trouble

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Hi.

 

Im having a little trouble with this homemade underglaze. The original recipe is this -

Ferro Frit 3124     33.3%

EPK Kaolin        33.4%

Stain       33.3%

I tried substituting at home with Gerstley Borate and Kaolin except if its just a hair too thick it bloats. Everywhere. Imagine the texture of a bumpy log. Fired to ^6 I suspect it's due to my dark stain which makes glazes bubble but any info about bloating would be greatly appreciated.

 

 

Edited by BlackDogPottery

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There's a lot of Boron in that mix. Excess Boron causes blistering. Try a non- (or low-) Boron frit, like 3110.

Out of interest, I've found that the best underglaze * mix is the glaze itself, minus any colorants/opacifiers. So my majolica underglaze * comprises 50% dry mix of the glaze ingredients (minus opacifiers), 50% stain, and underglaze medium. Or it might be 75% dry glaze mix, 25% stain, etc. depending on strength required. This works extremely well for all the stains I use, except one, which is so refractory that I have to add a little more frit (I use 3110 for this). Whether this works for you is going to be dependent on the physical (rather than chemical) properties of your glaze recipe, I suspect, and maybe which stains you use.

( * Actually, I suppose what I'm doing is more accurately described as 'in-glaze' rather than 'underglaze', but I imagine the principle remains sound.)

 

Edited by Sputty
Insufficient wittering.

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The recipe below is from George Vardy, he is the tech consultant at Mason stains. 

If you try it really don't skip the VeegumT (I've used macaloid and it works too). Chrome greens can need extra flux to melt,  calcium carb works.

EPK Kaolin 10 parts

Feldspar.     25 parts (I used custer)

Flint.            25 parts

Stain.           40 parts

Mix well with water, add 1 part VeeGum T that has been FULLY broken down in water, screen through a 100 or finer screen, bring to your painting consistency by addition of more water if needed.

When using very strong stains such as cobalt blues or chrome greens you may need to reduce the amount of stain if the fired color is too strong for your requirements. 

This can be used to decorate on clay or bisque. Be sure to dry fully before glazing.

Is it bloating in the clay or something else? Body bloating can be caused by organics in the clay not having sufficient time to burn out in the bisque or overfiring and the clay starts to break down and gas off causing the bloats. Are there bloats on the parts of pots without the underglaze or glaze that is giving you problems?

Edited by Min

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Underglazes are the one thing where I think it's well worth the money to buy a commercial product. They can go on at any stage- wet, leather hard, bone dry, bisque- they brush on nicely, and generally work great. Many brands are formulating them to work at cone 6, and you can find any color you want. There's always a little testing involved to see how your particular overglaze will affect the color, but that would be true of any homemade underglaze, too. If you watch for sales, you can get commercial  underglazes for as little as $5 a pint and they often need to be thinned down making them even cheaper. They are far more versatile than any homemade underglaze.

D.M.Ernst likes this

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13 hours ago, Sputty said:

There's a lot of Boron in that mix. Excess Boron causes blistering. Try a non- (or low-) Boron frit, like 3110.

Out of interest, I've found that the best underglaze * mix is the glaze itself, minus any colorants/opacifiers. So my majolica underglaze * comprises 50% dry mix of the glaze ingredients (minus opacifiers), 50% stain, and underglaze medium. Or it might be 75% dry glaze mix, 25% stain, etc. depending on strength required. This works extremely well for all the stains I use, except one, which is so refractory that I have to add a little more frit (I use 3110 for this). Whether this works for you is going to be dependent on the physical (rather than chemical) properties of your glaze recipe, I suspect, and maybe which stains you use.

( * Actually, I suppose what I'm doing is more accurately described as 'in-glaze' rather than 'underglaze', but I imagine the principle remains sound.)

 

Thank you. I really want to try that now. So just  %50 glaze and %50 stain ( or the other ratios) ?

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5 hours ago, Min said:

The recipe below is from George Vardy, he is the tech consultant at Mason stains. 

If you try it really don't skip the VeegumT (I've used macaloid and it works too). Chrome greens can need extra flux to melt,  calcium carb works.

EPK Kaolin 10 parts

Feldspar.     25 parts (I used custer)

Flint.            25 parts

Stain.           40 parts

Mix well with water, add 1 part VeeGum T that has been FULLY broken down in water, screen through a 100 or finer screen, bring to your painting consistency by addition of more water if needed.

When using very strong stains such as cobalt blues or chrome greens you may need to reduce the amount of stain if the fired color is too strong for your requirements. 

This can be used to decorate on clay or bisque. Be sure to dry fully before glazing.

Is it bloating in the clay or something else? Body bloating can be caused by organics in the clay not having sufficient time to burn out in the bisque or overfiring and the clay starts to break down and gas off causing the bloats. Are there bloats on the parts of pots without the underglaze or glaze that is giving you problems?

Thanks. Its definitely the underglaze. I've never had issues with the clay body. This recipe looks fine when its very thin, too sheer as if you can almost see the clay body through it. If you put another coat on it bloats... no matter. Even if its applied over the glaze, under the glaze, and just applied on its own. 

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3 hours ago, neilestrick said:

Underglazes are the one thing where I think it's well worth the money to buy a commercial product. They can go on at any stage- wet, leather hard, bone dry, bisque- they brush on nicely, and generally work great. Many brands are formulating them to work at cone 6, and you can find any color you want. There's always a little testing involved to see how your particular overglaze will affect the color, but that would be true of any homemade underglaze, too. If you watch for sales, you can get commercial  underglazes for as little as $5 a pint and they often need to be thinned down making them even cheaper. They are far more versatile than any homemade underglaze.

Thanks. Aren't they nice? I would be using commercial but I was looking for specific colors and the age old tale of the shipping prices. But honestly it probably would be easier in the long run.

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4 minutes ago, BlackDogPottery said:

Thank you. I really want to try that now. So just  %50 glaze and %50 stain ( or the other ratios) ?

Yep. 50% glaze (by volume, dry ingredients, minus colorants and/or opacifiers), 50% stain, plus whatever medium you use to mix it all up. I use a commercial underglaze medium (no idea what is in it), but whatever you're happy with, including just water, or water with a little glycerine, or whatever gives you a good brush-stroke..

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On 10/19/2017 at 7:42 AM, BlackDogPottery said:

Hi.

 

Im having a little trouble with this homemade underglaze. The original recipe is this -

Ferro Frit 3124     33.3%

EPK Kaolin        33.4%

Stain       33.3%

I tried substituting at home with Gerstley Borate and Kaolin except if its just a hair too thick it bloats. Everywhere. Imagine the texture of a bumpy log. Fired to ^6 I suspect it's due to my dark stain which makes glazes bubble but any info about bloating would be greatly appreciated.

 

 

That is Val Cushing’s recipe except he uses 3110. And should be applied thin. I have posted this several times. You may need to adjust your stain. It is basically: 1/3 of each , but stains vary in character. 

Marcia

 

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