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.
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.
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.
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.
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.
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. 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.
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.
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!