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Old 03-03-2017, 10:46 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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Old 03-03-2017, 01:52 PM
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Pete VanderLaan Pete VanderLaan is offline
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I don't think 30 grams in 7 lbs to be overkill. You could try 25. Chromes are really difficult to melt though and the dichromate really needs to be crushed before you try to add it. Adding to cullet is the hardest way to go and candidly 2100F is way too cold for that. What you see as black flecks are corundum stones and are the result of a cold melt with coarse dichromate. It's quite easy to crush in a mortar and pestle. When I teach that junk, I encourage students to give the dichromate a bath in lithium carb when crushing , but that's in a batch glass, not a cullet. Lithium is a powerful flux and it's not hard to throw the expansion all to hell. In that light, much as I hate the stuff, you could do the same thing in a bit of borax since it won't mess with the expansion much. The 20 mule team stuff at the grocery store will do.
Good Luck.
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Old 03-03-2017, 02:17 PM
Mitcheal Veenstra Mitcheal Veenstra is offline
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Peter, grind as in with a stone mortar and pestle? so the corundum stones come out of the dichromate once the chrome is fluxed in? I realize they are a crystalline form of aluminum oxide.

I thought lithium, but I wasn't sure if I could even use it with cullet, and I'd read also that it shifts the expansion quite a bit. I didn't really think about using Borax though it's a flux as well. When you say a bit, what scale of bit are you thinking?

I know coloring cullet is pretty basic and it will never be as nice as batch, but I had the electric color pot so I figured I'd start there. I've several books coming, Weyl, Scholes, and a copy of Courter's print of glass formulas. Volf is on my horizon and there's the Schmidt book I'd like to find that Cider Press put out a long time ago.. I'm starting from ground zero, or maybe a few inches above it with the craftweb archives and it's being an education. But it's a really neat feeling to open the door and pull hot color on a pipe or punty.

there's a gas color pot furnace in my future, I can see it also on the horizon...

Thanks for the advice and information. I appreciate it.
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Old 03-03-2017, 03:51 PM
Kenny Pieper Kenny Pieper is offline
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Mitcheal I think you are going to have a hard time getting chrome to desolve well with cullet. It is quite refractory and I have found it needs lots of heat even when ground well and used in batch.
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Old 03-03-2017, 04:12 PM
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Pete VanderLaan Pete VanderLaan is offline
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Kenny is saying it in a much less consoling way but it's too true. . When I melt chromes, I shoot at 2400F. 2100 ain't gonna cut it. If you really want a hopeless situation, use chrome oxide. It never works for anyone.
A mortar and pestle is nice. You can crush it between two bricks if you don't have the grinding tools but grinding is critical. . I used pieces of flat glass to do that, but really you need more heat and cullet is a tough way to go after green.

Also keep in mind Chrome is carcinogenic. Bullseye is still not allowed to melt chromes by Oregon. I also think that's an overreaction. Handle it with respect.
What will really help you out initially is to go in the Dave Bross method and mix very small quantities in a plastic bucket. It works fine. My first mixes, I did by hand and when I taught in Hawaii, I rolled a barrel down a hill into Claude Horan's Volvo. That was 1973. I can give you a formula that will fit your nuggets as a clear base. I think there's a 96 in the archives here that I wrote that is simple and doesn't use any exotic stuff. If it isn't here, PM me and I'll dig one out.

Good for you by the way. You will NEVER regret it. Especially after you see how much money it saves and how much faster you work.
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Old 03-03-2017, 04:28 PM
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Pete VanderLaan Pete VanderLaan is offline
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If Joe Piefer still has any copies of the Thuringen Helmut Schmidt material from Thuringen in 1925 that Fynn Lyngaard translated, BUY IT. The formulations all need to be adjusted and there's some serious typos but it's a jewel.

The good books have the life of a mayfly. We're trying to get pumped up about doing the book we've talked about over the last 15 years. I want to more write a "field guide to doing this" since no one ever talks about process and process is damn important.Once the comics are sold. Get Helmer's secret batch book from Joe too. That's remarkable. Just a stupid title. At Corning, you can spend days in the library like I tend to and it too is a goldmine, perhaps for a few years down the road. Someone else needs to carry this torch pretty soon.
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