chrome green?

[Kenny Pieper]

I'm wondering if anyone has had experience with melting a chrome green. I'm having problems with cords. I have been using the spruce pine base. For 25 lbs. of base I have 250 grams of potassium dichromate and 250 grams of copper carb. I've tried adding led and sodium nitrate to help dissolve the chrome but have since taken them both out and replaced them with soda ash. I've tried melting at 2350f. up to 2450F all to no avail. The cords are subtle. When sandwiched between clear and blown out they look like the vessel has been filled with water and then pored out. like tailings in a wine glass. I don't know what to try next. The color other wise is quite nice. Any help would be greatly appreciated.

[Rollin Karg]

How big is the pot you are melting in and what kind of pot? What does the temperature profile look like?

[Pete VanderLaan]

Take the chrome and first crush it. An old coffee grinder does this really well. Then mix it with some lithium carbonate to give it a sort of "bath" before melting.

Remember this is a carcinogenic melt. Also, I messed with your settings. try to post now.

[Kenny Pieper]

Well I'm using a thermal ceramics 1800 series 20# pot. They work fine for other colors. Often when I get refractory cords I can see when I gather some strands or cords coming from the side of the crucible. Not in this case. I've been throwing in around 2 lbs. at a time and then cooking from 2/4 hours at the end. One melt was with a cad. sel. red so I had the working temp quite low and the chrome started to come out of solution. This showed up as black specks. A higher working or holding tem. fixed that problem.
Pete I have been grinding it quite fine but the lithium thing is something I haven't heard of before. I presume I do that dry how much lithium would you suggest and do you think I'm trying to use too much chrome? Thanks for messing with my settings

[Hugh Jenkins]

Kenny, what chrome are you using? Oxide is one of the hardest to melt. You probably know to use Potassium dichromate, but thought I'd ask. It can be lumpy and quite granular though. Mix it separately with some soda ash and run it through a fine screen before adding it to the rest of the batch. It shouldn't be that hard. It does need oxidation so if you are using color base, add some nitrate. I don't know if the antimony in clear SB batch causes any problems with chrome.

[Rich Federici]

Dear Kenny,

When we made a chrome green it was 50g potassium dichromate crushed with 15g lithium carbonate in a mortar and pestle. This was maixed with 21 Lbs. SP87 Texas Sand, with Erbium.

I do not recall any cording, and Pete had suggested the lithium carb because our problem was black specks. My understanding is that the lithium carb assists the potassium dichromate to go into solution more completetly.

Hope this helps,

[Pete VanderLaan]

Thermal Ceramics? Jeez the stuff I do for science...

If I am reading that formula correctly, you are trying to add about five percent colorants in the form of both copper and chrome. That's a boatload. The copper will soften it but the chrome is going to be one unhappy and rather refractory camper. I would expect compatibility issues as well. This is certainly a color rod strength formulation.

The lithium is a dry additive and is designed to coat the dichromate with a really low temp flux. You would have to remove some soda or from the formula to offset the effect of the lithium. I would start with about fifty grams.

I don't think lead would be effective in the formula until you were up to about 10 percent and it would have to have the formula reworked completely. It would also really change the color.

Did you ever melt the enamel white?

[Kenny Pieper]

Hugh I am using Potassium Dichromate and grinding it quite fine. I did read in Weyl that it is good to stay away from reduction that's one reason I had the sodium nitrate in the first batches. My color furnace has a venturi burner on it and at high fire it tends to be a bit reducing. There is no antimony in the color base. I'll try the lithium or soda "bath" when I get back from the shows. I'm out of time for trying another melt just now. I'm thinking of coming out there in Sep. Hope to see you then. Thanks for your help

[Kenny Pieper]

Thermal Ceramics? Jeez the stuff I do for science... What do you mean?

Pete thanks for the suggestions. I will try the lithium. I an looking for a dark color.
I have done some melts of the duro with pretty good results. 40# at a time. I have run into something I have never seen though. At the bottom I'd say 5th of the pot there are lots of chucks and a very liquid type substance. Its so liquid that I cant gather it out. I have to scoop it. My only thoughts is that the lead is separating out. Next time I'm going to try to melt it hotter.

[Henry Halem]

Kenny,
Why don't you give Peiser a call and see what his suggestion might be. Heck you're in shouting distance.

[Pete VanderLaan]

Originally posted by Kenny Pieper
Thermal Ceramics? Jeez the stuff I do for science... What do you mean?

Pete thanks for the suggestions. I will try the lithium. I an looking for a dark color.
...and a very liquid type substance. Its so liquid that I cant gather it out. I have to scoop it. My only thoughts is that the lead is separating out. Next time I'm going to try to melt it hotter.

*************

might be arsenic. How hot are you melting it now? what percent arsenic? what percent lead? what atmosphere?

[Kenny Pieper]

Well this is a formula that came from Lino and if my math is right the arsnic is 8.21% and lead 20.6%. I've been melting at 3380f. In a pretty netural/ slightly reducing just until the sand isn't sharp in a thin thread. Usually that takes 1.5-2 hr. after last charge. It dosent foam as much as I was told it would. I only have to beat the foam back with a punty a couple of times. Its usually ready to make bars 2 hours later.

[Pete VanderLaan]

3380? That has to be a typo. It could be either 1880 or 2380 which seems very hot to me for that melt. . I knock the foam back with water. Get rid of the reduction.

[Kenny Pieper]

Your right that was a typo it is 2380. I remember you said that you did a melt of this stuff for Lino once. Do you recall what temp? It occurred to me that maybe the reason that I'm not getting that much foaming is that I'm melting at a lower temp than I should. Did you run into this problem of chucks in the bottom of the pot and this "separation"? Someone told me once that Lino had said that the duro likes the heat. It would sure be nice not to loose those last bars in the end.

[Pete VanderLaan]

when I melted it it was at about 2150. The only stuff I have ever seen of Linos that took heat was the Rosin black which was run at about 2500F.

With 20 percent lead, I can't see why it would need to be so hot and I think that is contributing to the potential lead separation in your melt.

Now I can believe that the chrome glass would take some heat.

[Kenny Pieper]

Wow with all that spar I'm surprised it could be melted at such a low temp. When we pick up a chunk from a bar it takes a really long time to get it hot. The stuff is like refractory, does not want to move. The clear on the moil requires lots of water to keep it stable enough to get the duro hot. You suggest trying less heat? Sure would be nice to melt at a lower temperature

[Pete VanderLaan]

I'll shoot you some other formulas I have for enamel white Kenny.
Keep in mind that Lino's was over a 110 on L.E.C. I think tiny quantities in each charge help. I always had a ton of foaming though. It just jumped out of the pot.

[Kenny Pieper]

I;ve always heard that the stuff foams like crazy and you have to beat it back with either another charge or water. Its curious that I don't have that experience. I wonder if its the arsenic I use. I have melted a few different formulas now. The Italian one being the stiffest. I like it that way cause when I use it in cane and put the cane either on the inside of a bowl or the outside of a piece it kind of stands out on the surface and leaves a texture.

[Scott Benefield]

Had you heard that Gaffer is now beginning to market an opalo duro? I haven't gotten my hands on it yet, but early reports are very positive and I like the prospects of having an easily available, reliable source.

[Pete VanderLaan]

Croucher has a great advantage in making the duro glass. In this country, Arsenic runs about 40 dollars per KG. It is heavily regulated. Croucher does not have the same constraints and the price is nearer to 1.80 per KG. He can make it for less than I would pay for the arsenic alone, not to mention that it is godawful stuff, poisonous and disgusting.

Go John.

[Scott Novota]

What does the "duro" mean?

Sorry to be such a know nothing.

Scott.
.

[R. Scott Johnson]

what change in the mix makes the regular crome green into the aventurine green? just curious.

[Pete VanderLaan]

duro is dense or hard.

The aventurines have more to do with high saturations of chrome held at low temperatures allowing crystals to form in the glass.

[R. Scott Johnson]

is that kind of like a crystal glaze on porcelain? it would be cool to grow crystals on a piece of blown glass.

[Pete VanderLaan]

I have never heard of doing that on Glass. In general, crystals on or in glass are something we really try hard to avoid. They are the equivalent of Cancer in glass.

[R. Scott Johnson]

but isnt that how some white glasses become white? I do understand the need to avoid devit, but the concept intrigues me. I know that the control factor is probably impossible though.

[Pete VanderLaan]

It's true. Cryolite functions by combining fluorine with either aluminum or calcium crystals. If the aluminum or calcium are not present, you don't get an opaque white.

But it isn't the same. The chrome stuff is "grown at about 1750F in the glass. Then the whole pot is cooled and the chunks broken up and hopefully sold. The same thing can be done with copper but it is more difficult. I don't think it to be possible to make an entire piece from either aventurine since you would have to get it too hot and then the crystal growth would be trashed.
The fluorine stuff can be made as either a cased glass or as a whole piece. It is not very attractive as a whole piece having a dull listless surface.

Push comes to shove, we really use crystals and colloids much more than avoiding them. I suppose it best to say you don't want crystals in your clear.