LotusBowl

Fast keystone project with some interesting aspects. This is LotusBowl, and it can be made in a single firing, although for finishing’s sake I did it in two.

I didn’t have a heckuva lotta luck with Mom’s Christmas present this year. The first, a pate de verre project, had a color change I didn’t care for. I decided instead to try an idea I’d had as part of the keystone projects (Keystone is what I call tack-fuse projects that involve balancing layers of glass in a mold so that the pieces support each other in a stable configuration while unfired, then gradually slide, slump or pull each other down into a final, tack-fused configuration).

A word about terminology…

“Are you doing a contour fuse?” she asked. “No such thing,” I said.

“Contour fuse” is a term making the rounds, and as far as I’m concerned doesn’t really mean anything. Glass is either fused flat or tack-fused, and from a technical perspective the real difference between the two is the potential for thermal stress introduction during the anneal (cooling) cycle. The only parts of a fused blank that are actually flat are the ones in contact with the kilnshelf; in most fuses the top will have volume bumps and a slightly rounded-over profile.

Not to mention the fact that “contour fuse” implies that the fuse is contouring to something–the mold, maybe?–so more properly that term would relate to slumping into a mold, not sticking to something.

The glass is all one piece, so the firing schedule is relatively easy to develop: Find the thickest part of the thinnest dimension (usually the height of the stack) and follow the annealing tables.

Tack-fusing is an entirely different beast: It’s basically separate pieces of glass, stuck together, with a lot more potential for annealing issues. Each of those pieces of glass will contract during the anneal, pulling away from each other and freezing in a lot of potential stress. To avoid it, you slow the anneal way way down. As a general rule of thumb, I multiply a tack-fuse thickness by 2 and fire at that schedule, then test for thermal shock (using a polarimeter). If it shows shock, I do it again, with a 3X anneal.

There are as many degrees of tack-fuse as there are kilns, I think, from sharp, absolutely square pieces that look glued on, to very rounded, soft pieces that look partially melted. The more rounded and melty, generally, the less anneal you’ll need.

Making LotusBowl

I’d wondered if I could layer concentric shapes in a flower pattern, cut Indian-style into a lotus shape, and get them to sag in a graduated color series, so you wound up with a “lotus flower” with a dramatic heart. Didn’t seem too difficult. Took three tries to get it right, though.

I first did this bowl in red, laid into BE’s 8647 square bowl mold. Came out OK, although in the end I wasn’t too crazy for the colors. A leaf broke in handling (and probably also because I rushed the cooldown), and an attempted refiring showed up some annealing problems, so I decided to start over. Along the way I thought up some refinements that made the second attempt much nicer than the first.

The blue version…

Please note: I didn’t exactly go from red version straight to blue. As usual, I made this design up in clear glass, several times, testing the results for annealing stress and to make sure the sides of the bowl could support the weight of the bowl. Once I was pretty sure I had a good formula, I moved onto the “real” thing. You might want to try that to get the measure of your own kiln and processes.

I use the BE 8647 mold quite a bit for keystone stuff. The contrast of curve and square create a nice tension you can play off with curvy shapes, and you have definite “sides” to your bowl so you can segment decoration into centers and edges. It offers a lot of possibilities for fibre paper modifications too.

I have clear plastic patterns of segments or sides of all my commercial molds, and I used the one of 8647 to try out in paper, making petal shapes until I had something I liked. Then I graduated the shapes down, cut some teardrop shapes for the center, and started playing with leaves. When you’re tack-fusing into 8647 you usually want to cut a long, thin shape for the each side of the corners–if you balance them correctly, one on each side, they’ll slide into each other, fuse, and give quite a bit of strength. But that would also have given me long “iris” leaves that wouldn’t exactly have fit the “lotus” thing. (Lotus leaves are usually roundish)

I finally decided to do a more compact version of the petal, and let it pivot on the outer petals. Hopefully, if it were long enough, it’d pivot down onto the petals as they flattened, and help hold the edges together.

I chose clear 3mm BE for my outermost petals and the leaves, and to keep the weight down, thin glass for the rest. I would have preferred using thin glass to get a delicate profile, but that’s too dangerous; people will almost certainly try to lift this bowl by the edges at some point. Thin glass will almost certainly break as it tries to support the weight of this bowl–using 3mm is much, much safer.

On the red version, I machine-ground all the component edges, and the effect was nice, but a bit crafter-looking. This time, I decided to hand-grind the edges of the 3mm pieces (so I could keep the roundness of the edge very organic). Then I fired all the individual components in a short full fuse.

The interim component fuse does three things: First, it rounds and glosses all edges so they look very finished. Second, it slightly thickens the edges of the thin glass components (I call it “lipping” the edges) which will help make the layers very separate and distinct, almost as if they’ve been carved. Third, I can sift on frit powder to create some texture. It doesn’t add much color (although it could) but the slightly raised lines catch the light and give a more organic-looking surface.

I sifted the powder on, then combed through it, following the general shapes of petals. Most of the powder you see here will darken and melt into the surface of the final piece, leaving only a slightly raised texture. About the only real color was on the center pieces, neo-lavender opal with a mixture of Plum and Violet Striker powder that did show up pretty clearly.

You can see the faint texture marks from the interim component fuse in both views.

After the components were out of the kiln, I set a piece of thin clear in the bottom of the mold and topped it with a mix of coarse frits in the same colors as the glass I was using. The frit serves in much the same way as gravel in a vase for flower-arranging–it holds everything in place while the sheet slumps into the bottom, and keeps some spacing between layers so they don’t completely flatten.

The coarse frit gives an interesting mottled texture, but it was the single most difficult part of figuring out the annealing schedule. All those frit pieces and frit balls connecting to each other brought the final anneal schedule up to 4X the normal schedule for that thickness; anything shorter showed massive stress halos in the polarimeter.

Another option might be to cut staggered squares of thin glass and rest the bottoms of the petals against them, in stair-step. The flat sheet is actually much less of an annealing headache because there aren’t so many separate joins of glass.

Once I’d figured out the schedule, it was pretty much a matter of layering in the components, outside to in. The hardest part, actually (and it wasn’t hard) was balancing the center petals so they’d stay aligned. I extended these beyond the edges of the outer petals–I think it looks a little less commercial that way.

I slid the leaves down in the corners until they literally balanced on the outer petals like seasaws–the petal edge would keep them from sliding all the way down, and as they settled into the corners they’d create a crease that looked like a leaf’s center vein.

Not a lot more to it than that. The center frit/fritball mix both anchors the center petals and gives a stameny-sepaley kinda feel. I got cute and sprinkled specks of crushed dichroic glass on the frit. Other than that, it’s pretty schmaltz-free. 😉

If you try this, remember one thing: The low-slow firing is crucial, and the anneal/soak in this case is a heckuva lot longer than the same thickness in flat glass-you’ve got a LOT of things going on in the bottom of that bowl, lots of tack-fused glass meeting at odd angles. But that’s about it. I should probably take a better picture of the finished work; if I do I’ll repost.

Nice exercise.