Murrini cane in a kiln: Jellyrolls
January 4, 2011 by Cynthia
Last time around, I talked about murrini cane, and the most obvious way to make them in the kiln: A murrini rod mold, AKA “rodpod.”
As I’ve said, I’m not pretending that anything I discuss here is my invention or brand new stuff: Murrini-making is one of the oldest glassmaking techniques. This is just a compendium of methods I use to make murrini in a kiln. You’re welcome to try these; please comment if you have other/better ways of doing this.
Murrini molds certainly can make some beautiful murrini, but it’s a grab-bag affair. The size of your cane is limited to the dimensions of the groove in the mold, rarely more than a foot in length, so the number of murrini per cane is relatively small.
Worse, because the components are harder to keep in place in these molds, canes aren’t particularly reproducible unless you stick with squarish designs. Gravity tends to smoosh everything into a squarish loaf shape, flattening out any round or symmetrical patterns. Stuff may or may not slide around, so it can be difficult to exactly reproduce the same pattern across multiple cane. If I need to cover two or three square feet with identical murrini, I make two or three times what I need and match it by hand; I usually wind up with two or three totally unusable cane from a rodpod.
BTW, this is part of a series that I *still* haven’t finished–never knew there were so many ways to make murrini in a kiln. Here’s the rest of the series:
- Murrini cane in a kiln: Sandwiches, Part I
- Kilnformer’s murrini you can buy
- Murrini cane in a kiln: The rod pod
- Kinda like peanuts
When I figured that out, I stopped using the molds and started making cane freeform. Freeform cane can be as long as my kiln permits, giving me more murrini per cane, and I control the diameter. The resulting cane can be nicely attractive, even if it still doesn’t look much like classic hotworked murrini:
To make them, you’ll need glass–stringer, strips, rod, noodles. And some scotch tape, the “magic,” frosted-looking stuff. My friend Carol Carson suggested it–she uses that tape to place glass precisely in a grid before fusing, and says it doesn’t leave a residue. (my tests agree with her)
You’ll also need fiber blanket and ThinFire paper, and some hi-temp wire and heavy mullite dams, enough of the latter to dam both sides of your murrini without moving.
For both methods, it helps if you’re working on a sheet of float/plate glass–easier to clean, and you can use the edge of the glass to start your rolls.
Method 1: Tear off three strips of scotch tape, two about an inch long, one around 9 or 10 inches long. (These measurements are approximate–don’t get carried away measuring)
The last inch or so of the long piece of tape back on itself, sticky sides together, to make a pulltab, and set the tape down, sticky side UP, on the glass. Tape down both ends with the short pieces of tape, leaving maybe a half inch of the pulltab exposed. (This makes it easy to pull the tape back off the glass.) It’ll look like this:
You’re going to build up your jellyroll from the center out, so start with whatever glass you want to be in the center. I like to use a standard glass rod, and I set it on the end of the tape nearest the pulltab. For added punch, see if you can find a compatible rod with a variegated center. Bullseye sells a few, and makes many more as special production glasses (below); they’ll give additional detail to your cane.
Wrap a strip of scrap paper all the way around the rod once, marking its circumference. Mark that length on the tape with a Sharpie marker–that’s the first “ring” in your murrini. Add the width of 2 of the widest components in that ring (1mm stringer here) to the original circumference, multiply by 3.14 and measure out that far for the second mark. Keep doing that until you’ve got four or five rings marked. It won’t be exact, I promise, but it gives you a guide as to how much glass you’ll need for each layer in the cane.
Lay down enough stringer to fill the tape to the first mark–this will be the first ring around the rod. Then lay the second ring, and so on. I like to alternate opal and transparent glass rings and I try to keep the palette pretty simple.
When you’ve filled the tape all the way to the last mark, burnish the glass pieces gently against the back tape to ensure they’re flat and in place. Now take more tape, and run a strip down the middle, cross-wise (above the first tape) on TOP of your glass. Add a second and third strip at each end and make sure they’re all well-adhered to the glass.
Now pull up on the tab you made and gently lift the entire assembly off your work surface. It should come away easily and hang in the air like a venetian blind; if it doesn’t, smooth the tape down firmly and try again.
Set the assembly back on the glass, with the first rod off the float glass to get things started. Begin rolling it away from you, firmly and tightly, and roll the whole thing up just like a jellyroll. It takes a bit of practice to do this without disturbing the order of the rods, and it can be difficult to keep the glass tightly rolled.
The instinct is to roll it in the center; actually, you’re better off rolling from either end to ensure the ends are tight. You MUST keep the layers as tightly coiled against each other as possible. If it gets out of order, unroll it, straighten things out and start again. The assembly will gradually pull itself together and roll in the right direction for you.
Eventually, you’ll get a tight roll like this.
Make sure the glass pieces are straight and even all the way out to the ends, then wrap each end in more tape to secure them. That’s pretty much it.
Method 2: In method 1 you’re actually creating a spiral coil, and while it goes pretty fast, it’s hard to keep the rings precisely aligned in any semblance of pattern. It also works best with relatively thin, uniform pieces of glass, such as commercial stringer. If you want to use cut glass strips, lots of noodles and other interesting things, or if you want to more precisely control the pattern, build the cane assembly vertically. Again, this ain’t rocket science, it just takes a bit of coordination.
Start with a rod in the center as before (this isn’t strictly necessary, but a rod gives you a nice foundation to build on). Stand the rod on its end, perfectly vertical, and attach a 5-6 inch piece of tape near the bottom.
Snug the first piece of glass (still vertically) against the tape, bring the tape over to cover it and burnish it down. Add the second piece the same way and move around the rod until you’ve completely surrounded it. Burnish the tape down over the whole thing and start the second row. If you plan a bit, you can usually build combinations of stringer, noodle, rod, etc. that actually fit evenly around the assembly.
When you’ve got enough, run your hands up the length of the assembly (being REALLY careful if you’re using cut strips), and make sure everything’s aligned. Then tape first the center and then the other end. That’s it.
Prepping for the kiln
If you just toss these in the kiln and fire, the tape will vaporize, the components will spread out and you’ll go through the usual “glass wants to be 1/4 inch” nonsense. Obviously, you need some way to keep the bundle intact enough that it will keep its shape during firing.
Start by wrapping the roll in ThinFire VERY TIGHTLY and taping it up. ThinFire is kinda brittle; if you have trouble getting it to cover the ends of the roll without breaking or bulging, try misting it with a little water to soften it (just don’t soften TOO much or it will fall apart).
The ThinFire has absolutely zip structural integrity once the binders burn out; it’s primarily there to keep the outside of your cane smooth. 1/8 inch fiber paper does the structural work–wrap your ThinFired package in that.
I like to cut a piece that’s about an inch bigger than the diameter of the cane assembly and the same length. Then I cut two more fiberpaper pieces, each just slightly wider than the diameter of the end of the roll and that dimension plus a couple of inches long. I tape them across each end of the cane assembly, then wrap the whole thing in the big piece of fiber. I tape it every three inches or so to secure the fiber paper and provide a stable base for the next step.
You can fire it as-is, and it will flatten into a capsule shape. The components will slide and distort one another so that you wind up with cane that almost looks like a potmelt. This murrini, for example, started out with twin blue rods in the center, surrounded by amber noodles and a couple rings of red. Obviously, they were badly pulled apart.
Once I’ve finished the fiber paper wrap, I cut enough pieces of wire (about 2x the diameter of the roll) to place one every 3-4 inches down the entire length of the cane.
Starting in the middle, I wrap a wire around the cane, twist the ends together so they lock, and go to the next. (Just twist each side into a “U” shape, then lock them together–they stay reusable that way) I wire only on the taped areas–this keeps me from accidentally tearing away the soft fiber paper. Where I haven’t (below) you can see how much it cuts in.
Whatever y0u do, the shape will be closer to round if you dam the bundle with heavy mullite brick.
These are fairly large cane (at least in these examples–you don’t have to use this much glass to make a cane), and they’re extremely well-insulated. They also have a LOT of air pockets created by the spaces between pieces of glass.
In my kiln, they work best if I fire at about 50DPH between 1000F and 1250F, hold at 1480F for an hour (for you Centigradians, that’s 10DPH between 538C and 677C, hold at 804C for an hour), and then anneal for slightly more than the thickness of the wrapped, pre-fire assembly, about two inches for these cane. I still get bubbles, so at some point I’ll probably lengthen the process time to see if I can clear a few more.
As always, your kiln’s schedule will be different. You can most certainly pull back on the schedule and see just how little heatwork you can apply and still get a solid cane; sometimes that can reduce distortion.
The usual murrini choppers that work on rod-pod cane will work on this, up to about a half inch. Beyond that, you’ve got to be pretty strong to even make a mark on the cane, let alone cut it neatly. The stuff is too precious to saw through–you’ll lose the thickness of the saw blade with every cut. Even if that’s just 1/16 of an inch, it means you’re losing at least a couple of murrini for every foot of cane.
So far the best method I’ve found to chop thicker cane is to give the murrini choppers a bit of an assist with a heavy hammer or sledgehammer. The cane MUST fit into the jaws easily. I position the cane in the choppers, where I want it to split, and squeeze the handles until it’s secure. Then I whack the top of the choppers (NOT the blade) with the hammer. The cuts this produces can be remarkably thin and even, although I tend to get a lot of offcuts. (If someone knows a better way, speak up, please!)
The pieces fly an amazing distance and they can splinter, so obviously you do this wearing goggles and gloves. It’s best to chop inside a box or enclosure–helps you find your murrini after it’s shot off the end of the cane like a torpedo.
So far, no horizontal kiln method I’ve tried produces a perfectly round, distortion-free cane. Here’s how much they change, even with the double-wrap/wired/heavy dammed treatment:
So at this point, I stop looking at horizontal fusing, and start looking at vertical fusing. And casting. More on that, later.