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Old 03-03-2017, 09:46 AM
Mitcheal Veenstra Mitcheal Veenstra is offline
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color melt question

After many long years of saying I was going to start melting color in my own shop I finally got off my duff and reworked my old electric color pot and fired it up to start my journey of discovery with cullet colors for now.

I'm on my third attempt at color, the first was easily successful, the second successful in some ways, not so much in others(but not bad)..

the third, was odd.. and I think I know what happened but wanted to run it past the collective here. We decided to swap out pots and try the simple potassium dichromate green. The recipe that I pulled form the archives here calls for 30 grams of dichromate with 7 pounds of fritted clear. My base glass is spectrum 2.0 premium. I fritted the glass into a bucket of ice water, so I got nice small fines/frit. I used damp frit and made sure that the frit was well coated with the dichromate, well mixed is half melted....

After I had loaded the pot and let it run overnight, holding at 2100F (what I typically work spectrum 2.0 at in my shop) I checked the pot. There was a kind of dark haze in the middle of the top of the melt and the bubbles I expected as it was fining.. I went to poke the melt with a punty and the dark haze 'splashed' under the punty. Two thoughts went through my head, one was it's 2100 degrees, that's not water.. the second was, what the heck was it?!

I would assume it's some of the potassium dichromate that's puddled up on the surface after not fluxing into the cullet. I stirred the melt, pulled a color sample and found it was yes streaky and black specs and very green... I stirred again and then let it fine out for another 12 hours.

That night we pulled glass from the pot. The first piece was the worse, black specs, more bubbles than I liked.. The second looked pretty good, still a few black specs, but not nearly the size of the first piece. The third looked pretty clean. I know that the black specs is unmelted chrome that failed to flux in because chrome is notoriously hard to get into solution, especially with a commercial cullet.

now, to my question, was I correct? Was that puddle dichromate? How do I avoid that in the future, should I cut back the amount added to the cullet, melt hotter, or something else? Because the glass at the bottom of the pot seemed cleaner, I think perhaps the right answer is to cut back on the dichromate on a future melt, but I wanted to see what was your suggestions.

Thanks!
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