Coolth #2: Quoin Basket

>>>>Coolth #2: Quoin Basket


If you’ve read the previous post, you read that I got a couple of nice experiments out of the kiln tonight. The first is a fibrous-looking, almost woven basket (which actually does have some weaving processes) out of stringer.

The second, the subject of this post, uses small pieces of sheet glass instead of stringers and noodles. I’m calling it Quoin Basket because the brickwork edges, in BE Yellow and Orange, resemble quoins in classic building architectures.

This is another keystone project, where I’m balancing pieces of glass so they support each other during firing and the whole piece can be completed in one firing process. Done right, it should transfer the load to the lowest points of the mold so that gravity actually helps compress the glass together during firing. Hopefully by compressing the pieces together, I get a better, more stable tack-fuse.

Why go to all the trouble to fuse in the mold instead of tack-fusing flat, then slumping? Well, the slump can distort and stretch the flat blank as it fits the glass into the mold, which makes exact placement more difficult. By positioning and stacking pieces of glass directly in the mold, I get exact placement with no distortions and more control over the tack-fuse texture. And I’m not sure that some of these pieces, such as the bowls in the Stacks series, could be produced with conventional flat-then-slump techniques. It would be extremely difficult (and the glass gods would have to be in a REALLY good mood) to get the piece I’m working on here to slump like this.

Plus, it’s nice to have some instant gratification since my first love, casting, can take weeks or even months to get to a finished piece.

The Quoin Basket is made of small pieces–mostly squares and rectangles–of Bullseye transparent glass. They’re stacked into the mold (in this case, Bullseye’s 8647 curved square mold) from the center out. Each piece is fitted into place like a jigsaw puzzle, and builds on the piece beside/below it. This mold has steep sides (about 45 degrees at points), with sharp-angled corners. I figured that if stonemasons used quoins to cope with such things on a building, I could do it in a mold with glass, and it worked.

The “brickwork” that makes up the mass of the bowl is actually the supporting structure, and it’s of standard 3mm BE clear (good way to use up lots of clear scrap). The bottom is reinforced with a subframe of thin clear noodles under the four BE yellow squares. It’s filled in with coarse Crystal Clear frit and a teal circle of thin glass in the center. (the frit catches on the noodle infrastructure and helps lock the bottom pieces together, to add stability)

I put more clear frit around the edges of the base, to act as a kind of mortar for the “brickwork” that rises above. I wanted the weight of the glass above the frit to push the mass of glass down, into the frit, where it could fuse more tightly together. In turn, the frit would push inward, moving the rest of the glass into the center until it stopped.

Once the basic structure was in place, I balanced a second layer of glass, the triangles, circles and squares shown below, so that they’d push against the “brickwork” and help keep it flat against the mold. (I was worried that any sideways slippage of the “bricks” might cause one or more to pop out of the structure, and if that happened the whole thing might come down.) I also figured that adding some additional weight to the mass of coarse frit would again push the glass toward the center, providing extra stability.

(And, in case you hadn’t noticed, the second layer forms arrows that kinda illustrate the vector of the compression actions. Yeah, yeah, it’s a bit literal.)

This piece grew organically, a polite way of saying that I made it up as I went along. The other reason for sticking the blue and green “down arrows” on each side is to cover up the glass “bricks” that don’t meet evenly in the center. In this experiment, there’s a lot of irregular “chinking” going on because I figured out that I wanted the glass bricks to entirely cover the sides after I’d already stuck on the edges. In a real piece, I’d do some measurements and size the bricks so that they precisely met in the middle.

Decided the final balancing act looked a bit uneven (and since I use superglue to hold pieces in place while I’m building, there was no way I could remove pieces and trim them to smooth out the edges). So I topped it with thin strips of 3mm Deep Cobalt Blue and half-circles of 3mm Spring Green. The blue strips balance on the understructure of the arrows, keeping them in place, and the green half-circles push against the blue strips.

Here’s the finished piece, from the top. Can’t decide if it looks Italian or Chinese. Probably more to the Italian side, kinda Tuscan (well, the basket part, anyway).

I give stuff like this a LOT more annealing soak and cooldown time than would be warranted for a solid, flat-fuse piece of 6mm glass. The glass thickness varies from 3mm (and possibly thinner at some of the frit joins) to 10-11mm in spots, which is one reason to stay on the conservative side when annealing.

The bigger reason, though, is that these tack-fused pieces are really lots and lots of little glass joins, most with sharp corners that can freeze a lot of stress inside. They need plenty of time to relax–I START calculating at 4X a normal anneal and work it out from there.

Was pretty sure the brickwork would hold, but had my doubts about those arrows and the edge wrap. As long as those pieces all stayed balanced on the point of that triangle, I was fine, but any slip would send them to the bottom.

So…was really cool to see they’d held, and the piece was intact. The blue edges came in a little farther than I’d have liked as the piece compacted toward the bottom. It would coldwork off in a heartbeat and I could firepolish the result, but I’m a little leery of subjecting this piece to a grinder–too easy to shiver it apart. It actually feels quite sturdy, but there are a LOT of tackfuses that have to hold in this one.

Learned a lot on Quoin Basket, gotten a couple of really neat ideas to explore in a real piece, and discovered some new balancing acts that will look cool when I do it.

All in all, a success.

2016-05-16T00:53:13+00:00

Comments welcome! (thanks)