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Strontium Glazes


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#1 clay lover

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Posted 26 April 2011 - 07:10 AM

I have been wanting to use some strontium glazes that I found, but was told by a clinician that uses them a lot that if they were cooled too slowly, they would be rough.
Do any of you have any experience with this? , I don't know how slow is too slow.

I use a lot of Mastering Cone 6 Glazes in my kiln, they do great with a 500*/hr drop to 1900, a soak there of 30 min, then 125*/hr to 1700, then off. I get nice satins and mattes with that rate. Is that too slow for strontium?

#2 Matt Katz

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Posted 26 April 2011 - 01:50 PM

There is no such thing as "too slow for Strontium." Strontium is an Alkaline Earth Flux just like Magnesium, Calcium, and Barium (and Lead and Zinc). It does not have any particular behavioral trend that the other Fluxes don't.
Glazes that are properly formed mattes will be matte independent of cooling cycle. The same with gloss.
Let your kiln cool naturally and if the results are pleasing to you then, there you go.
If it is a matte glaze you can influence the density of the crystal growth in the matte (properly formed matte glazes are crystal that grow in a gloss base).
You can increase crystal growth by cooling slowly (or firing down) through the beginning stages of the cool down. But as the growth cycle depends on the viscosity of the glass it doesn't last for too long. once the glaze solidifies, it isn't going to crystallize.

#3 clay lover

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Posted 26 April 2011 - 04:49 PM

So is there a way to know what temp the glaze solidifies at?

I have had the experience of cooling Hesselberth's matt glazes too quickly and ending up with very shiney surfaces. When ramped down from 1900 to 1700 at 150*/hr with a 30 min soak at 1900, they are lovely satin saurface.

In asking the orriginal question, I am only repeating what a well know instructor told me about the glazes he uses, and I saw the results of his firings the next day, super satin surfaces.

These strontium glazes are new to me and I don't want to screw up an entire kiln of nice pots by not paying attention to what I was instructed to do.

#4 OffCenter

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Posted 27 April 2011 - 10:25 AM

There is no such thing as "too slow for Strontium." Strontium is an Alkaline Earth Flux just like Magnesium, Calcium, and Barium (and Lead and Zinc). It does not have any particular behavioral trend that the other Fluxes don't.
Glazes that are properly formed mattes will be matte independent of cooling cycle. The same with gloss.
Let your kiln cool naturally and if the results are pleasing to you then, there you go.
If it is a matte glaze you can influence the density of the crystal growth in the matte (properly formed matte glazes are crystal that grow in a gloss base).
You can increase crystal growth by cooling slowly (or firing down) through the beginning stages of the cool down. But as the growth cycle depends on the viscosity of the glass it doesn't last for too long. once the glaze solidifies, it isn't going to crystallize.


I think controlled cooling is sometimes overdone. I followed a suggested cool down program that was pretty complicated trying to get glazing similar to Steven Hill. I spent a lot of time on it and made the firing even longer and more complicated thinking there was a minor improvement each time I added a hold or a slow-down. I was very happy with the results of 6 months of experimenting, but then when I was getting ready for a show, my electric kiln with the computer died and since I didn't have time to fix it, I did a "Hail Mary" firing in my electric kiln that only has a kiln sitter, but I fired it one cone higher (cone 7 instead of cone 6). The results were great. I could not tell the difference between pots that had been fired to cone 6 with a very long, complicated program and pots fired quickly but a little hotter. At least in this instance, the extra heat-work to get from 6 to 7 equaled a complicated cool down program.
E pur si muove.

"But it does move," said Galileo under his breath.

#5 clay lover

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Posted 27 April 2011 - 07:58 PM

The schedule that Steven Hill gave me isn't complex, it's pretty much heat em up sorta fast, and cool em off even faster, open the kiln at 500*. That was what he did at the workshop I attended, and the pots were superb. He drops from a peak temp with a long soak , by 9999*/hr, down to 1600 then another shorter soak, then off. Strontium glazes are the foundation of what he is doing. Since he has perfected his look at ^6, I would think he would know what he is doing concerning cooling those glazes.

#6 OffCenter

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Posted 28 April 2011 - 08:04 AM

The schedule that Steven Hill gave me isn't complex, it's pretty much heat em up sorta fast, and cool em off even faster, open the kiln at 500*. That was what he did at the workshop I attended, and the pots were superb. He drops from a peak temp with a long soak , by 9999*/hr, down to 1600 then another shorter soak, then off. Strontium glazes are the foundation of what he is doing. Since he has perfected his look at ^6, I would think he would know what he is doing concerning cooling those glazes.


I didn't mean to infer that Hill doesn't know what he is doing. My post was a response to Katz's post (the reason it was quoted). My point was that my trial-and-error experimenting agreed with his more scientific approach. First of all the suggested cool down wasn't Hill's and I made it clear that I made the program more complicated thinking that each complication improved the firing. Your little remark at the end of your post was not appropriate.

Jim
E pur si muove.

"But it does move," said Galileo under his breath.




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