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-   -   Weird melt results.. (http://talk.craftweb.com/showthread.php?t=12359)

Josh Bernbaum 07-06-2019 03:09 PM

Weird melt results..
 
Sorry, didn't know how to properly title this thread, but I'm super confused..
I've done lots of melts over the years and I haven't seen results like this last one I melted a few days ago. I've been doing phosphate melts lately, 5 total, all mixing in with the SP Plain batch (no erbium). And I know, calcium etc, but I have been getting decent results for the most part. I'd been struggling with the fit but on that 5th melt I finally got it to fit the SP w/er clear I melt also.

Fast forward to my most recent melt this week, where I just wanted a transparent copper blue. I scooped out as much as possible from the bottom of the pot before charging this mix that was the SP plain with 0.77% black copper oxide. It's a gas furnace, my crown is in good shape and my melt times and temps were similar to what I've always done for melts like this.

I've done many, many ionic colors this way over the years but this melt was full of 'snot' that looked like semi see-through white-ish clumps. All throughout the 80 lb pot. My first thought was that, even though I'd scooped out the previous phosphate melt as best I could, that whatever residue from that was making snot in this melt. BUT, what's even weirder, is that compatibility was off, something I don't think I've ever seen with less than 1% addition of colorants to a transparent base. The ring cup I made didn't fare well on the saw, and the only info I could glean from it was that expansion of this blue might be low. My next thought then, is could I have gotten an 'off' bag of SP plain? Unlikely I'd think, as in my experience SP have been so consistent which is one of the many reasons I've stuck with their batch over the years.

Not sure what to do next but I've 'swabbed' the walls of the color pot today with some clear from my main furnace, scooped that out of the bottom, and I'm charging maybe a third of a pot of plain batch next for a 'rinse' that I'll scoop out to try and fully clean this thing. Am I missing something else I should be considering? Thanks in adv, and hope everyone had a good Fourth.

Best,
Josh B

Pete VanderLaan 07-06-2019 04:55 PM

I think copper is the single most underappreciated way to move expansion I run into constantly. I don't tend to think it even acts in a linear calculable way. John C and I have gone around with each other on how weirdly quirky it actually is.

I have taken my silver opal base and added 25 grams of red copper to it and then used it blowing against a casing with the silver base. It works sometimes. Sometimes, it doesn't. Chuck used to refer to it as emetic and I can only relate to that term when it comes to barfing. I think he meant that it caused a precitious drop in viscosity and I have seen that. Don't discount viscosity mismatch.
Simply put, it does very unpredictable things to glass. When I made color rods, I never was able to make good rod from copper transparents. I did not have any trouble with the copper rubies. The differences were really minimal The worst was a turquise blue opal. Mary Beth absolutely hates the color so we rarely have to lose sleep over it. A career in fast foods might be a path forward.
I would discontinue using SP as a base for phosphates.

Josh Bernbaum 07-07-2019 08:10 PM

Thanks, I just mixed and batched a cobalt blue today instead of trying to deal with the copper, and even though I prefer the blue from copper I just want to make some blue cane that has a bit of density. I have gotten the copper additions to fit in the past, but it was less copper than this problem melt and there was some iron in those mixes as well which, according to one of the spreadsheets I looked at, might help mitigate what the copper is doing to the expansion? And I have no idea what it's doing to the viscosity as you mention. Still not sure what to think about the snot in the last melt, but I tried to clean the hell out of the pot before melting this cobalt today.

I'd like to try one more phosphate before I shut down for rest of the summer, and I'm taking a look at mixing from scratch instead of the SP again. Curious, do you think it'd be a waste of time to try for a manganese purple phosphate if I have enough potassium in the mix (which I think I've noticed can help the manganese purple tones)? I'm asking because I thought I'd heard opal purples are a tough go for whatever reason, but maybe I heard that wrong?

Pete VanderLaan 07-08-2019 08:05 AM

I think your main problem is the calcium in the SP87. I mix using strontium and barium and could probably get rid of the strontium. I just rarely make the stuff.

As to the mang purple, does the SP base have antimony? I think not. It functions two ways going from the tri to the penta and also the mono valences accomodating both redox reactions. The O2 is not friendly to the color and in sp it would tend towards the brown. Gold would be better.

I think Dave's formula is a good place to start and then adjust it.

The viscosity on the copper is not particularly consistent. As the temp drops, it goes through some very fluid stages. I always had a hell of a time with fluorine blues making it into bar. I can normally pull a very consistent rod at 18 inches. Not with that stuff.

Josh Bernbaum 07-08-2019 09:37 AM

Yes, I'd definitely avoid trying any Mn purples on SP as a base, I've seen those brownish results. But I've had some good purples in the past using your zinc/potash cad sel base from the 2013 class. So at some point I was thinking about adjusting the Brossphate to have more potash and less sodium, no nitrates, and maybe more zinc? to see if I can get a decent opal purple.

Pete VanderLaan 07-08-2019 10:31 AM

I think Barium or strontium / potash might be better for that application. 3% zinc is called for in a cad sel but I think it maybe unhelpful in the phosphate. Potash fattens that stuff up quite enough but indeed is better on the color.

Jordan Kube 07-10-2019 08:36 PM

This sounds like poorly mixed ingredients or wrong proportions. That's really the only time stuff like this happens to me. I'm sure you mixed just fine, what you scooped out of the bag may not have been mixed as well.

Pete VanderLaan 07-11-2019 08:09 AM

SP Color base is not mixed at all. It's just the chemicals dumped in a bag.

Wrong proportions is an entirely different matter.

Josh Bernbaum 07-11-2019 10:11 AM

Just to report back on this, since having that weird melt with the copper that had a bunch of unmelted snot in it and wasn't at all compatible, I have done one transparent cobalt melt that was mixed with the SP pelletized batch (not the color base). I made sure to clean out the pot as best I could, and that seemed to help and I got a typical nice melt again which was a relief after I had been second-guessing everything. So it seems to me like the Occam's Razor most likely scenario is that the previous phosphate melt I did (mixing with SP) before the problem one with the copper, contributed to the unmelted snot in the subsequent ionic copper melt. And I suppose using too much copper percentage threw off the expansion too much. Living and learning I guess..

Dave Bross 07-17-2019 09:24 AM

The basics for phosphates:

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.


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