Glass fusing with mixed results

Last summer, I bartered with somebody for a cardboard box of glass shards from a stained glass studio. It’s a great variety of colors and sizes, and was labelled COE 96. (All glasses have a specific coefficient of expansion. That refers to how much they expand and contract when heated. You can’t mix different COEs or the project cracks. This will become relevant later on.) It’s been staring at me reproachfully ever since and begging to be used. I don’t know how to do stained glass (yet) but I do have a kiln capable of doing small glass projects. I usually use it for annealing beads, but it is a pretty flexible model. With all this free compatible glass laying around, I decided to try some fusing projects in hopes of working up to slumped and/or cast items.

My ancient Paragon Q11A.

My ancient Paragon Q11A. It stands on a heatproof surface when in use; this pic was taken when it was cooled off and just on the floor out of the way.

What the Paragon website says a Paragon Q11A looks like.

What the Paragon website says a Paragon Q11A looks like.

The problem is that my kiln is a little… unorthodox. I inherited it from a friend. Its serial number plate says it’s a Paragon Q11A. I think it’s either a very early model or one that’s seen a lot of things in its life, because it’s nowhere near the spiff and sleek blue beauty on the Paragon website. It stands freely on its little legs, without the protective skirts of the newer models. Its controller is attached to the side like an afterthought, and the heat gauge is even sketchier. It consists of a thermocouple literally poked through a hole in the top. That said, it’s worked like a champ for all the years I’ve been lampworking. I’ve never had a problem using it to batch anneal glass beads.

Last night, I decided to try my hand at glass fusing for the very first time. I’ve seen it done a few times and read a bit about the technical aspects. With a box of free glass taking up space in my shop, it was time to give it a shot. I assembled a handful of small projects, a larger thin thing I hoped would make a nifty suncatcher, and half a dozen beads that had cracked on me (glow glass is very unforgiving) and were gonna be thrown out anyways. I dug up a suggested firing schedule for COE 96 glass and got going. My old beauty doesn’t have a programmable controller, so any firing schedule requires constant attention. My usual strategy is to take a dry-erase marker and put a dot of paint on the temperature I’m shooting for, so I can look up from whatever I’m doing every few minutes and check it without walking over.

Finished projects. Lots of problems.

Finished projects. Lots of problems.

These are the small fusing projects. I don’t have any glass cutting equipment yet, so these were made by selecting glass that happened to be the right sizes. I knew they’d be a bit lumpy. A few came out great; the majority were disappointing. I swear to you that top bar had a layer of clear glass when it went into the kiln. I don’t know if it turned opaque from devitrification or just was a mystery glass that was supposed to do that, but it makes me sad.

What was supposed to be the back side.

What was supposed to be the back side. The base layer was swirly clear and white.

Pendants with glow glass powder. One spread out more than expected and swallowed its wire bail. Both seem to have cooked their glow powder, 'cause they don't glow.

Pendants with glow glass powder.

Clockwise, two pendants of clear with glow powder between the layers. I can’t use the glow powder well in lampworking because it tends to burn while being encased. That stuff is very temperamental – it’s hard to use because it makes the glass brittle and very thermal shocky. It also loses its glow ability if heated over a certain temperature (direct flame, for instance). One spread out more than expected and swallowed its wire bail. I used a bit of pure copper wire between the layers of glass. One was bent into a swooping spiral; the other plain. Both seem to have cooked their glow powder, ’cause they don’t glow. I really like the looks of that one on the right in particular, though, even without any glow in the dark capability, so it’s not a complete loss.

Front side. Serious incompatibility with light blue.

Front side. Serious incompatibility with light blue.

At the 7 o’clock position is a layer of white glass with shards of color and a bumpy top clear piece. I was really hoping this would be cool. As I said, I don’t have glass cutting gear, so I knew there’d be some overlap with that slightly too large clear top piece and I hoped it would look good anyways. For some reason this one didn’t heat enough and failed to slump all the way. Turns out to be a moot point, since the light blue chip inside it is clearly a different COE than the rest of it and has cracked all around.

Back side. Note the precise cracking around the light blue shard.

Back side.

This is the back side of that piece with the bumpy top. You can clearly see where that light blue adhered to the glass above and below it, but then when it cooled it proved to be more flexible (or less so) than those two layers, and so there are stress crack lines around it where something had to give. This can’t be saved. It’s probably going to crack completely eventually. Even remelting it won’t fix this. Sigh. At least the glass was free! Unfortunately, knowing now that there are mixed COEs in this box, I can’t comfortably use it for any more hot work since this problem could happen again at any project. Next skill to conquer: stained glass!

At 9 o’clock is a yellow base with some color and a clear top. It devitrified and looks hazy. Not a complete fail, but not what I was going for. I tried to flash vent the kiln to drop it quickly from the slumping temperature (~1400*F) down to a slightly cooler range, since sometimes glass will develop a crystalline structure if allowed to cool slowly. DSC09349 I’ve heard that most glass manufacturers have tweaked their recipes to avoid that problem, but clearly not the maker of this batch. I flash vented by turning off the heating element and cracking open the kiln, but it just didn’t drop fast enough. I think the fire brick holds a lot of heat. Even with the kiln off and the door open a few inches, it took long enough for the thermometer to drop just from 1400* to 1100* that I was starting to worry about cracking something and shut the door again. I don’t know if I wussed out or if that’s an actual issue with this kiln.  I’m happiest with the center piece: some iridescent clear over a strip of teal and two dichroic(?) or iridized black chips. That came out perfect.

Suncatcher idea. Not enough glass made it get very sharp & pointy.

Not enough glass made it get very sharp & pointy.

The largest project was this random assortment of stacked shards. It wasn’t a failure, technically speaking, but not what I was hoping for. And at least this time, the error was purely mine. I didn’t stack enough glass layers (only one in most places) to avoid the ends from getting sharp as the glass relaxed and drew towards the center. I deliberately left holes between the shards so I could string wire and hang it in the sunlight. As I said – not a complete failure; it just doesn’t look like the image I had had in my head when I was putting it together. That’s an inexperience issue, not a technical problem. It’s still pretty and none of the glass cracked or devitrified, so that puts it ahead of the rest of the class. 😉

Last but not least, the arrangement of disposable cracked beads I put in there mostly out of curiosity. The bottom ones were glow in the dark Laurel medallions that had cracked before I figured out the appropriate annealing cycle for that material. I’d tried to slump them a little bit to heal their cracks but with no luck. So I put a loop of copper wire through their holes and decided to just flatten them out and see what happened. The wire is so I can still string it on something if I’d liked the effect.

Cracked beads.

Cracked beads.

That… was a mixed success. On the top left one, it worked okay. The bottom two spread out farther than their wire loops, and swallowed them into the glass. The top right one rejected the loop completely and spat it to the surface. Ha. The red ones were two beads containing Pennsic dust that had cracked, so I split them. The wire on the top right one can be removed, leaving it still an oddly shaped bead. The center is a perfect cabochon. Yay! Left side was a layer of encasing clear that had cracked off but still contained dust, so I slumped it anyways. It too made a neat cabochon.

So, verdict? The kiln worked more or less okay. My inexperience with the process led to at least one problem, probably more. But the real kicker is that random COE shard of blue. If there’s one non-COE96 piece in there, there’s probably more. So that rules out this entire box for hotworking projects. I can still use it for stained glass, but melting two different colors in contact with each other is asking for failure. Back to the project board!

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10 Responses to Glass fusing with mixed results

  1. Sharon says:

    Very interesting! I don’t know a thing about glasswork, so I *like* the pointy “failure.” I think it’d be awesome hanging in a window! And I agree, the non-glow “tooth” pendant is fantastic.

  2. Robin says:

    I think they all look pretty darn cool. I know they weren’t what you had envisioned, and so in your mind they’re just not right, but a buyer doesn’t have to know that. 😉

    Also, I don’t think you should give up on the whole box because you found a piece with a clearly different COE than what you were told was in there. Why not keep experimenting? It’s art, after all. Don’t limit yourself.

    • Elinor says:

      I’m not gonna give up entirely on the box. I think I’ll just try to switch to a different art form (stained glass) that doesn’t require melting any of it, so the COEs are irrelevant. I’m too much of a perfectionist to tolerate seeing a piece crack. 😉 It makes me too annoyed.

      • Robin says:

        Well, I meant you should give the kiln stuff a few more tries, but I hear ya. From one perfectionist to another. =)

  3. M. Sotherden Art Glass says:

    Hey 🙂 to my knowledge nobody makes 96 Coe in clear hammered (that’s the piece that topped the multicolored shard embedment that didn’t work out. If you want to haul the box to Pennsic- I can maybe take a look at it & see if we can spot any definite non Coe-96. And when you take stuff to fusing (re: the overlapping project that came out all pointy) that will happen when you use kiln wash as a base for fusing on. I highly recommend bullseye thinfire paper. Keeps that from happening as much, although when you have single layers like that it is MUCH more likely to happen than not.

    • Elinor says:

      Thanks! I’ll take all the pointers and help I can get. 🙂

    • Elinor says:

      Oh, any suggestions for flash venting? I’m a little freaked out by just opening the kiln door to crash cool it, but is that what I’m supposed to be doing?

      • M. Sotherden Art Glass says:

        Yep. Put on your safety specs so you don’t burn out your retinas from the high temp glass color and throw on an asbestos mitt baby 🙂 open it WIIIIIIIDE up at 1470 ish until 1150 ish.

  4. M. Sotherden Art Glass says:

    I don’t know of a glass company that makes 96 with a hammer texture in clear – that’s the piece that you used as a top for the piece that didn’t really work out with the multi coloured shards – I agree with you that the blue shard is also suspect in that one because of the cracking around it… Second, Just something to keep in mind – if you’re using kiln wash on the shelf that has a tendency to make pointy ends stay pointy when fusing. Single layers of glass will do this more than doubled layers of glass for whatever reason, but is very common and fusing on kiln wash seems to exacerbate the problem. I recommend using bull’s-eye thinfire paper to alleviate this. Last, I make no promises on my detection skills, but if it’s worth calling the box to Pennsic, we can take a look through it and perhaps definitively weed out some of the stuff that is not 96 Coe.

    • M. Sotherden Art Glass says:

      Sorry Sarah the internet barfed and swallowed my first reply so the second reply is redundant. I didn’t realize they both posted.

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