Thread: Phosphate Opal
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Old 04-11-2009, 03:41 PM
Dave Bross Dave Bross is offline
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Here's a link to an old post of mine explaining "the fix" for chunky phosphates:

http://talk.craftweb.com/showthread....e+opals&page=2

Here's the text from there to save everyone a trip:


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I've been trying to get a phosphate opal without the "texture" for a while now. The answer turned out to be mainly in the modifiers.

You don't use more than 3% calcium, 5% strontium, or 9.5% barium while using at least .4 - 1%, but not more than 2% zinc to help retard the formation of the dreaded surface crystals, and 2-5.5% phosphorus.


I (finally!!!) found all this in an old Corning patent, US patent # 4536480. I've done some melts with the calcium, strontium, zinc and phosphorus (no barium) in those ranges and it works beautifully in terms of no surface ugliness and the usual great beauty of phosphate opal.

The patent also suggests 1.5% fluorine to get a little apetite cryatalization going, but as a wire melter kind of guy I left that alone, and I'm quite happy with the opal I got without it. a bit of reading between the lines suggests you will do fine without the fluorine, making...

"glasses wherein the opal phase is essentially non-crystaline; i.e., the opacity results from the presence of immiscible glass phases"

After all those melts of "sandpaper" phosphate opal I think I'll pass on any kind of crystals in my phosphate melt.

Obviously, you would have to batch this one from scratch because no stock batch goes that low in all those modifiers.

I like sodium tripolyphosphate for a phosphorous source. It's pretty common at chemical suppliers, it's used in a lot of cleaning formulations.
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Just screen the STPP and it will be fine. It really almost doesn't even need that but I do it just in case there's something unexpected in there.

Don't worry about contact mixing lithium with it, it will go down just fine as-is. After everyones struggles with getting phosphate to melt you're going to be surprised at how easily this melts.

Y'all are just going to LOVE what you get if you go to the trouble of batching these. Colors are amazing done up in phosphate. So much more stable and less toxic than fluorines too.
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Last edited by Dave Bross; 04-11-2009 at 03:44 PM.
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