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Low Fire Matt Transparent


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#1 siggy

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Posted 06 April 2010 - 05:02 AM

Hi I joined today and would like some advice about low fire transpafrent matt glazes. I cant sen to find a recipe for a transparent matt that does not alter the colours of commercial stains ie. draining the colour out of pinks and purples.

#2 Sherman

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Posted 06 April 2010 - 08:19 AM

Hi I joined today and would like some advice about low fire transpafrent matt glazes. I cant sen to find a recipe for a transparent matt that does not alter the colours of commercial stains ie. draining the colour out of pinks and purples.


Siggy, what makes a glaze matt is either crystallization of the glaze materials or unmelted material floating in the glaze. Both of these things prevent transparency, the first by scattering the light, preventing it (and therefore your eyes) from getting through it in a straight line. The second by simply blocking/reflecting light back to your eye before it can get through the glaze. I have seen some commercial low-fire glazes labeled as "matt" that are satin and what one might call "clear," but in my experience they are not really transparent, and they do some of what you have already seen with stains and oxides, for the same reasons mentioned above. I have no idea how they do it (perhaps milling materials more finely than we are able to in our studios), but they might be worth a shot. The only one I have seen in use is from Amaco, but I am sure there are others.
One point: the colors are not being bleached (or burned off), they are simply being blocked by other particles in the glaze or made less visible because of the diffraction of light.
Sherman Hall
Editor, Ceramics Monthly
Co-host, Ceramic Arts Daily
http://www.ceramicsmonthly.org

#3 siggy

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Posted 06 April 2010 - 03:38 PM


Hi I joined today and would like some advice about low fire transpafrent matt glazes. I cant sen to find a recipe for a transparent matt that does not alter the colours of commercial stains ie. draining the colour out of pinks and purples.


Siggy, what makes a glaze matt is either crystallization of the glaze materials or unmelted material floating in the glaze. Both of these things prevent transparency, the first by scattering the light, preventing it (and therefore your eyes) from getting through it in a straight line. The second by simply blocking/reflecting light back to your eye before it can get through the glaze. I have seen some commercial low-fire glazes labeled as "matt" that are satin and what one might call "clear," but in my experience they are not really transparent, and they do some of what you have already seen with stains and oxides, for the same reasons mentioned above. I have no idea how they do it (perhaps milling materials more finely than we are able to in our studios), but they might be worth a shot. The only one I have seen in use is from Amaco, but I am sure there are others.
One point: the colors are not being bleached (or burned off), they are simply being blocked by other particles in the glaze or made less visible because of the diffraction of light.



#4 siggy

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Posted 06 April 2010 - 03:47 PM

Thanks Sherman for that explnation . It is strange that some colours like pink and purple seem "bleached" under a matt transparent more than others I am going to try the stains over the matt glaze as in majolica fashion and see if that works better. I have mixed a batch of the majolica matt base I have seen on the glaze pages, in 10 successful low fire recipes, and the glaze gave an almost mottled effect with the stains, and the pink was swallowed up completely, although it was matt!

#5 Sherman

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Posted 07 April 2010 - 09:13 AM

Thanks Sherman for that explnation . It is strange that some colours like pink and purple seem "bleached" under a matt transparent more than others I am going to try the stains over the matt glaze as in majolica fashion and see if that works better. I have mixed a batch of the majolica matt base I have seen on the glaze pages, in 10 successful low fire recipes, and the glaze gave an almost mottled effect with the stains, and the pink was swallowed up completely, although it was matt!


Siggy,

One correction to my original reply: Suspended particles in a glaze do not make it matt, but they do tend to make it opaque.

If I'm looking at the same glaze you are, it contains 38% Gerstley borate, which itself is has perhaps 20% calcium. Calcium has a bleaching effect on iron, so if your stains contain iron, this could be part of what's going on. Please keep in mind this is all a bit of guesswork on my part, since I have not tried this glaze.

For transparent matt, I do still recommend using a commercial product. All the best!
Sherman Hall
Editor, Ceramics Monthly
Co-host, Ceramic Arts Daily
http://www.ceramicsmonthly.org




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