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Monday, July 21st, 2008

Time Event
This past weekend owens888, spongiform, and I took a glass flameworking class at The Crucible. In flameworking you burn propane with oxygen (from a gas cylinder, not just the O2 in the air) to heat glass tubing and rods to thousands of degrees, melt them into blobs of color and pattern, and shape these blobs into marbles, pendants, figurines, vessels, and paper weights. It was much fun. Class ran 10a-6p Saturday and Sunday (a so-called "intensive" session) during which we three, and four other students, were taught by two glass faculty (Jay Bridgland and Tara Murray). The faculty to student ratio is great: we each had lots of attention from the instructors and we could easily get questions answered. Much of the time was free flameworking time, during which we could work on anything we wanted, with breaks for instruction and demonstrations of several fundamentals. From memory, these are my notes:

Safety: the flame is 5500F. Don't touch. Really; not even for a split second. Glass is hot, too. Burn salves and bandaids are in the first aid kit. If you blow glass too thinly then blow it out, it will turn into a fine glass dust that's pretty bad to inhale. Don't do this. If you do, Tara will water spritz the space above your work area to reduce the floating glass, then make you clean everything up.

Melting glass. Always rotate glass in the flame, to keep the heat even across the piece. Uneven heat causes things to bend and slump in unattractive ways. When you're working on a piece of glass you may need a handle on the end. This is called a punty. Heat the end of the punty and the glass, touch the two together outside the flame, wait a moment, and you're done - handle'd. To cut glass, heat it in the flame, and either (a) pull it apart in the flame, briskly, or (b) rotate the two pieces apart from each other like bicycle pedals, winding up the extra glass as you go. Do this in the flame.

Gravity marble. Attach a punty to a 5/8" rod stock. Flame cut the thick glass 2-3" from the punty. Begin heating the end and rolling the punty for even heat. This glass will become slumpy soft and begin to ball up. Move the heat along toward the punty, building up the ball. Too egglike? Hold the punty down. Too mushroom-like? Hold the punty up. Use gravity as your free tool, your third hand. Eventually, you have a ball. Make a cold seal: let the ball cool a little, heat another punty, then just touch it to the other side of the ball. It's a cold seal b/c the work is colder than the punty. Don't worry, it'll hold. Now, flame cut the original punty off right at the end of the ball. You can remove extra glass: heat, touch a cold punty to the hot glass out of the flame, pull, then flame cut the thin strands left. Repeat. With the extra glass removed, continue shaping the marble, using gravity to assist. Do not get the flame on the cold seal. When you're done, set the marble in the graphite mold, just so the marble doesn't roll. Hold the punty up, tap it with a tool near the seal, and it should come right off. Heat the marble side of the seal to smooth out any flat lump left by the cold seal, and you're done. Don't touch the marble, it's still hot.

The torch. The torch has two hoses and two knobs, one for propane (on top, in red) and one for oxygen (side, green or silver). The propane is the first gas on and the last gas off -- don't ever run the oxygen without propane. A little propane, flint spark to light, then add oxygen. You can make three types of flame: neutral, reducing (more propane than oxygen; not all the propane burns), and oxidizing (more oxygen than propane; hotter).

More, next post.
Canes, colors, and swirl marbles
We used borosilicate (eg, Pyrex) glass in the class. It's a stiffer glass, seems to cool to a stiff tension more quickly than soft glass ("seems to" because I only infer this, we didn't do anything with other glass in the class), and is apparently the best stuff to learn with. The instructor made a demonstration by dropping a marble on the concrete floor: the marble bounced. Lesson to learn: don't worry if something falls on the floor. It may not crack, and if it's just been in the flame, it'll hurt way worse to catch it than to remake the piece from scratch.

The glass rod and tubes we use as base are all clear. Color comes from adding metals to the glass and heating them up to form crystals. Silver, chromium, cadmium, and rare earth elements are popular sources of color, and each can produce a wide variety of colors, depending on how the crystals grow and how the glass is heated to activate the crystal growth.

A cane is a length of glass that's had color applied to it. You heat the base material, hold it beneath the flame, heat the color, then paint the color on the base. Apply just a bit of pressure as you do this. I found that holding the color steady, and moving the base beneath it, worked best. Use a small flame if the color rod is thin (eg, a stringer).

We created swirl marbles by first creating a cane, hot sealing a punty to the end, heating the cane, twisting as you heat, then pulling the last punty off. Form a marble at the end, this time using the graphite marble shaping tool. The glass will have the twisted color strands from the cane and will be clear inside (from the base glass). Cold seal the end, flame put the original punty, finish shaping the marble, then remove the cold seal.

Canes with contrasting colors work well. It's okay to leave gaps in the color; these'll turn into clear glass. If you heat the cane overall the colors will melt into the cane. You want to do at least enough of this to fuse the glass together. Twisting is good but don't twist too much, else the colors will turn muddy. Eg, a 45 degree twist wrt the long axis of the rod will look nice, but an 80 degree twist will be too thin and won't look great.

The marble shaping tool is a graphite block with divots of various sizes and a handle at one end (eg, here). You do not just push the hot glass into a divot in order to make a hemisphere. This would produce a harsh crease in the marble and wouldn't help you smooth anything out. Instead, think of the divots simply as rings, or bottomless pits. The purpose is to run the ring around the surface of the marble; a perfectly round marble will touch the rim of the hole at all times everywhere. If the marble is eccentric, moving the rim around the marble (or rotating the marble around and about the rim) will smooth out the lumps. Time in the flame and rotating the entire piece for even heat and gravity treatment will smooth out the surface. Yes, this truly works! The graphite can withstand tremendous temperatures, so you can introduce the very hot glass to the tool. I found what worked well was to let the glass cool just to a medium red, down from a very hot glow, before placing it on the tool. Also, it worked best to rotate the punty (spinning the marble) as I lay the marble into the divot, with the punty horizontal, so as to avoid pushing the rim into the soft glass and creating a crease. Choose a divot that's at least one size smaller than the marble. You don't want the marble to fall inside the divot; the rim of the divot should do all the work.

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