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-   -   Are chrome-containing glasses prone to devit? (

Josh Bernbaum 01-26-2019 01:50 PM

Are chrome-containing glasses prone to devit?
Sorry I haven't added anything to this part of the forum in a while, but I'm really glad we now have this section specifically on color chemistry etc. So, I'm just curious if my new hunch might be accurate that chrome-containing glasses might be prone to devit? Here's why I'm asking: I've recently been doing some pieces where the color in the murrini cross-sections I'm using is uncased and 'exposed'. I've done several pieces using the same methods and the first and only-to-that-point devit I'd seen on the surface was in murrini made with one of Gaffer's transparent greens (Lime green they call it). I'm first rolling up a sheet of the murrini slices and making a 'cup' out of it to stuff with more clear glass later in making the final piece. I first noticed the devit on the surface of the cup, just slightly. After reheating and stuffing and making the piece, the devit was slightly more noticeable. So a while later I tried a similar color green made by Reichenbach, R-24. I was a bit surprised to see the same kind of devit. I don't want to case this murrine layer, that might be a solution here but not the kind of look and feel I'm after in these pieces. This is all kind of subtle, but it's there and it sort of makes that section of the piece look etched. I don't totally hate the look but it's not what I intended and I'm mostly just curious what's going on with these transparent greens. I'm guessing both are done on a lead base. One other thing to add which might be contrary to my hunch about the chrome is that I've done one or two murrine pieces made with one of my homemade chrome melts in the past and didn't notice devit. But my chrome content was only about 1-2% if that's a factor at all, and this melt would have been dichromate added to SP batch as the base.

Pete VanderLaan 01-26-2019 03:01 PM

I do not know. It's a good question for John. I can say that I've certainly seen lots of iridescence on green bottle glasses that have solarized and I think them to be chrome based. I do know that the EU has become concerned with Chrome leaching from glass in landfills.

I've always thought of lead glasses as allowing what I would call "packing " of metallic oxides into glasses. When making the black, extra lead has to go into the goop to get the metals into solution. My black has a significant addition of chrome. I grind it finely with lithium and sodium before it goes in the mixer. I don't think of 2% as being a small addition at all. Chrome seems capable of causing significant expansion shift as well.

Josh Bernbaum 01-26-2019 04:11 PM

I'll definitely try to pick John's brain about this at the class this April. One other interesting tidbit that I forgot to mention in the previous post was that I had a friend (Jerry Kung, a glass blower/tool maker from Oakland who some of you may know) visiting this past year, we used this same green murrine on a piece we made together. He is always thinking outside the box, and looking for different ways of doing things. So as an alternative to the 'cup-stuffing' I've been doing, he wanted to try doing a Swedish overlay with the murrine rollup. I remember seeing this devit on the surface after the rollup, but after we smeared the Swedish overlay onto another clear bubble and then made the piece, no devit detected. That formerly inside surface of the rollup, which was now on the outside, still had the exposed green on the surface but no devit. That seemed odd to me, not sure what got rid of or inhibited the devit by doing this.

Eben Horton 01-26-2019 08:09 PM

Iím gonna go out on a limb and suggest that your chrome is coming out of solution and is not devitrifying. As Pete suggests with using lead, the lead will give something for the chrome to hang onto.

Pete VanderLaan 01-27-2019 08:51 AM

That's not quite what I suggested. I do know that chrome will create crystals as in "Aventurine" in the right concentrations at the right temperatures but it's not a glass I have much experience with. I do think anytime you have a color hanging around 16-1700F, it is in the happy range for crystals forming. Color rods certainly have to go through that range. I'd still ask John.

Jordan Kube 01-29-2019 09:28 PM

Chrome does weird stuff in boro. Crystal growth, etc.

Larry Cazes 01-30-2019 01:42 PM


Originally Posted by Jordan Kube (Post 142668)
Chrome does weird stuff in boro. Crystal growth, etc.

I use a lot of unencased chrome based borosilicate aventurine. It is somewhat prone to Devitrification.

Pete VanderLaan 01-31-2019 08:02 AM

I did ask John and he reacted to the quantity of Chrome in the glass Josh made the same way I did. 2% is a lot of chrome and is a big difference from 1%. Big big difference. Overworking glass which frequently occurs in murrini has some unpleasant side effects.

Josh Bernbaum 01-31-2019 04:37 PM

My apologies here, I shouldn't have just guessed about that 1-2% addition of chrome. It had been a while, and I might have been thinking of a different melt, but went back to my notes today which say I used 0.2% dichromate in the mix. But just to re-explain, I did not see any of this devit or whatever the hazing is on murrini made with my 0.2% green. I did however, see it on murrini made with both one of the Gaffer greens and one of the Reichenbach greens. I'd imagine the chrome content was higher than mine in these commercial bar-colors, not to mention the different bases. I usually go for a 'light-wash' of density in my transparent colors that I've melted, versus a higher density that might be more well-suited for making color bars.

Pete VanderLaan 01-31-2019 05:01 PM

Damn those decimals!

We didn't really focus on it at all but glasses really do undergo change as they are heated and cooled. Chromes do, Cad Sels do, fluorines do, phosphates do, gold glasses do in my experience. It celebrates you getting to make your own glasses. They are tailored

As glass processes get more and more convoluted, the material is asked to do things beyond the stability of the eutectic. I remember Steve Weinberg saying, "Jeez, it's only glass."

Some folks expect the material to be something it's not- unchangeable. It's very changeable and maybe not in ways that you like. Can the problems be overcome? Sometimes, not always.

It provides us privilege and humility all in the same moment.

I really hope you enjoy John. Who else out there is taking the class from him. I'm envious.

Josh Bernbaum 01-31-2019 06:25 PM

Wow, eutectic. Have to admit I had to look it up, great word though.. What you mentioned about glasses undergoing changes brings to mind one noticeable shift I witnessed in the heat treatment cycles that these murrini tend to go through. (besides the green issues I've already been scratching my head about) I've melted your fluorine mix several times as you know Pete, and I really have liked working with it for the most part. I'd been hitting the expansion pretty spot-on with most of those melts (with ring testing). Also, a piece I made with a pre-made, cooled and reheated part with the fluorine white survived subsequent coldworking. But the murrini I made and used with it was a different story. That would have gone through 3 heat cycles: one for pulling filigrana-style cane with it surrounding a duro color, two for bundling those canes, reheating and pulling into murrine, and three for incorporating those slices into a piece. Both tries didn't even make it through annealing. But I did have a piece survive that was just made with the murrini, no clear case. So that said, I'd been curious if or how one could go about adjusting a formula to be more likely to remain compatible with the base glass even after multiple heat cycles.

Pete VanderLaan 01-31-2019 07:22 PM

Go read Dan Schwoerer's paper on viscosity. I'm not apologizing for referring to Eutectics.

Keep in mind that in opals, crystals grow and they collapse and they grow again. Each time, a little less and it changes the viscosity as they change. They also change expansions understandably.

When Chuck and I were designing the glasses, we were targeting where things were the first time, not five times down the road. Down that path lies madness. . What you are doing is not something we were marketing towards. I would suggest that you set aside specific parts of that, and try making some pieces with more, and some with less sodium. See what happens. Follow the glass.

Rich Samuel 01-31-2019 08:36 PM

My dad bought his Heathkits and parts for DIY projects at Eutectic Electric in Long Island City. This was back when nobody lived in LIC.

Pete VanderLaan 02-01-2019 10:05 AM

Cut it out.

It strikes me that one needs to consider the classic formations that help define what is and what isn't a glass. If I look to a material that seems to have no softening point and seems to have an irregular molecular structure that doesn't crystalize forming regular molecular structures then I want to see what makes it stop being a glass. Do you think adding 5lbs of cobalt oxide to 20 lbs of a good formula will still be glassy? 5lbs of clay? 5lbs of alumina?

If I added 15% alumina to many glasses, I don't expect it to be a glass anymore. If I added 20% china clay, I wouldn't expect it. Those are clearly higher limits but the eutectic as shown by Scholes gives direction to various materials that can be and are added to the material and the general direction the material is heading. So, do please read Scholes, Modern Glass practices and look at the illustrated page showing the tendencies.

I understand the error, sort of. The difference between .2 and 2% is large and not noticing the error is worrisome in itself, particularly if one is asking a question about devit, the formation of regular crystals in an irregular molecular structure.
If I went back to the early period in modern studio glass, I tend to think that Bullseye was right about looking for a 90 L.E.C. instead of the 96 that we have but 96 is never going to go away. So, we have this stuff which is a bit less stable than their glass and when you dink with it in ways that industry never contemplated, heating and cooling forever, chances are you'll have problems. Again, crystals grow, they collapse, they grow again until spent and your visual experience with that glass is altered. The color's gone. The opacity is muted or gone. Glass is not static. It gives you some elbow room but it does not have infinite patience with you.

I would think that bathing the chrome in lithium , assuming it is introduced as a sodium or potassium dichromate would really help flux it but even so, there are limits. When Gaffer makes a rod, they don't endlessly heat and cool it. They make rod based on sound chemical expectations that the studio inevitably screws with.

Recently, I've gone around with the issue that this is somehow being kept secret as a sort of plot. It's not. I don't have a fix it answer about the chrome. I don't have a fix it answer for making people quit using boron as a universal flux . I just know the kinds of troubles to expect from it when present in glasses containing other molecular compounds. Not unlike Calcium and phosphorous. We know what will very likely occur combining those two materials. Avoid it.

It's confusing though.

Josh Bernbaum 02-02-2019 06:59 PM


Originally Posted by Pete VanderLaan (Post 142685)
I understand the error, sort of. The difference between .2 and 2% is large and not noticing the error is worrisome in itself, particularly if one is asking a question about devit,

I'm trying to be less defensive in my life and relationship lately, but I have to speak up with a reminder that I'd just guessed when I originally wrote down having 1-2% of this colorant in my last green mix, which was over a year ago. After looking at my notes, in which I do try to write down as much info as I can about each melt, I then saw that it was only 0.2% in that older melt. I mostly buy and use color bars and don't have my color furnace up and going most of the year, so I admit my recollection of the percentages isn't as good as it could be. Sorry, but just felt the need to mention again.

Pete VanderLaan 02-03-2019 09:13 AM

The "cut it out" was addressed to Rich, not to you. I think the chemistry of glass is inevitably a difficult subject and I struggle with trying to explain what I know and don't know. It's worth noting how many stuffed volumes in binders I have doing melts over fifty years. It's equally worth noting how many of those melts have been abandoned by me.
There are some compounds that if you add too much, there will be profoundly bad results. Chrome, Fluorine, lithium, barium, boron are a few of the biggies. Then just simple overdoses of cobalt, copper, nickle, cadmium, selenium are going to give you heartburn and me a new crucible customer. Given the notion that anything above 1% as an additive is probably going to throw the Linear expansion all to hell is reasonable indicator of wretched excess but is adjustable. Sort of. I remember when in reading Mark's notes which the classes all got that his opal began to devitrify after seven hours on the blowpipe as a beacon for you to think about. I continue to suspect that much of this modern glass will have issues somewhere down the road. But, like with global warming, it's not our problem, right?

The amount of literature available to the modern glassmaker is profound and deep compared to what I was aware of as a young man. Volf alone is huge. Color rods now satisfy what most glassblowers want. When I was a kid, color rods were not in this country. I still have an old promo folder from RISD showing all these sample experiments in color testing on the cover. They were very proud of that.
That's pretty much gone now. From my point of view its disappearance has diminished the potential for great artwork, not to say that there isn't still great artwork, there is. Just try to think about what it would be like if you could gather 5lbs of Gold Ruby. It would be pricey but not impossibly expensive. It's true of every color out there, so, I keep hacking at it. I'm glad you do as well.

Pete VanderLaan 02-03-2019 04:49 PM

I also spent a bit of the day reviewing the differences between Cr3 and Cr6 differences as to toxicity and color. It was a good part of the State of Oregon vs Bullseye glass. That Cr6 is Erin Brockovich land. You ain't gonna get that lime green with a Cr3 and all of that depends on furnace atmosphere.

Scholes has an excellent quote from Morey on the glassy state. Just really good explaining why things go south... and why shouldn't they? "It's only glass. "( Steve Weinberg)

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