Monday, August 6, 2007

The Allure of Hot Glass

A glass store in Rome, demonstrating the infallible beauty of glass. It's easy to love it, but be careful of its shiny attraction: it can get vulgar sometimes...

If you've ever been to a glassblowing workshop and watched the glassblowers doing their stuff, or seen a demonstration at a historical museum, you'll know what I mean when I say that blowing glass is a dance, requiring a specific and delicate choreography, often involving many people working together.*

Most people don't think of glass as sensual, but it is - when it's hot. Glass is really a magical medium. Its melting point is at around 2400 degrees Farenheit (1300 Celsius), so touching it is out of the question. The incredible, lush pliability of glass when it is hot can only be felt through the end of a blowpipe, never with your hands. Wet wooden tools, wads of wet newspaper, and steel implements become your fingers and hands when you are interacting with hot glass; the love affair is conducted at a distance. This takes quite a lot of time: to learn to feel the quality of the material, judge when it is ripe for movement, know when you can shape and pluck, push and pull. It must be kept constantly, constantly moving, for gravity exerts an inevitable pull, tempting the hot and drooping glass to pool on the floor, and your job is to dance the rolling dance, turning and turning so the glass doesn't follow gravity's will. The sensuality of it begins to hit you as you get better at the dance; the sweatiness, the manipulation of softness, and the titillation of that desire to touch and necessary distance is inescapable. It is truly hot stuff.

Looking into the Glory Hole

A good glassblower can feel the gradual slowing of movement as the glass goes from near-liquid to sluggish, a warm taffy consistency, to an eventual hardening which signals that the end is near. If you are not finished at this point, you are in danger of your work cracking, breaking, or popping off the punty (long steel pole) and shattering on the floor, so you must keep heating it, using your sense of distance-touch and the glow of the glass to tell you when it is hot enough to work, but not so hot that you lose all the detail and shape of what you have done so far.

And it is hot! Working with the furnaces, dipping the blowpipe into the crucible of molten glass or reheating in the glory hole (special reheating furnace), you feel that you are suffering a form of localized sunburn, a crystalization of your sweat. Your skin radiates; you don't notice you're sweating because all of you is at the end of that pipe, that pole, moving the glistening stuff around.

My friend Pamina Traylor, a masterful glassblower and sculptor, at work with a reheating torch: more localized than the glory hole.

Curiously, it is this need for heat that was the undoing of much of the forests of Europe. As Venetians took their glass skills and traveled to other places (which they weren't supposed to do - but since when does that stop people?), glass workshops were set up all over the continent and the British Isles. In 17th century England, James the First finally banned charcoal burning because of fears that the forests would be decimated - not because he loved trees, but because they were fast approaching a place where there would be nothing to build ships out of for the navy. Losing the charcoal-burners, who transformed trees into hot-burning fuel, meant that the glass industry, one of the most fuel-hungry industries around, had to recalibrate their furnaces and their glass "recipes" in order to convert to coal.

This led to several improvements in the glass. First of all, the coal produced a purer, high temperature product. Secondly, and oddly, Admiral Sir Robert Mansell (the naval man who advised the King to ban charcoal burning) retired from the navy and started his own glassworks. He experimented with adding iron and magnesium to the mix in an effort to make colored glass, but instead came up with a much stonger type of glass.

(One offshoot of this was that the English then were able to start fermenting wines in the bottle, since the glass was now strong enough to withstand the pressure. The French didn't start being able to make champagne with a second fermentation until the mid-1800s: their wood-fire blown bottles weren't strong enough.)

A typical Dale Chihuly piece, about 14 feet high, made with over a thousand pieces

Historically, glassblowing was always an activity either Guild-centered or exclusively industrial. Then in the late 1950's Harvey Littleton, an American ceramicist who grew up in the glass town of Corning, New York, began experimenting with glassblowing in a studio, with the help of Dominick Labino, a glass scientist who designed a simple furnace. By the early 1960's he had begun teaching others what he had learned, and the modern studio glass movement had begun. The Littleton style of blowing, however, was a sort of bootstrap affair, doing nearly everything oneself; which is a bit like insisting on building your house with your own two hands - you can do it, but why?

By the late 1960s studio glass artists had begun turning their faces to Venice, where artisan (rather than industrial) glass was still being blown by highly-skilled people. A conversation was begun between Venetian and American glass artists which is still going on today.Dale Chihuly himself, a student of Littleton and one of the best-known glass designers in the world these days, was and is a big proponent of the team style of blowing, creating work that would be absolutely nowhere without many hands to help. In fact, Chihuly takes this idea a bit further, allowing highly skilled blowers to do the hot-glass dance for him entirely, since he has lost an eye and doesn't have the requisite depth perception.


To my mind, one of the most wonderful, the most magical parts of the blowing process, aside from the sheer addictiveness of the act itself, is the way you get to come back the next day and see the things which were once liquid transformed into cool, crystalline hardness, through some almost incomprehensible alchemy. The glass has gone from being naturally hot, orange, and in motion (cold equalling danger), to cold and immovable, brittle and clear.

The nature of glass is finicky; it must be cooled slowly, or it will shatter. The thicker and larger the piece, the longer it must take to cool, or stresses within the structure of the glass (yes, it is indeed a type of silica, with a couple of other things in there) will be too much for the object, and it will give way, sometimes years later. This process is called annealing, and it is done in a sort of hot oven called an annealer, where glassblowers put their work when it is finished. In a modern studio, annealers are programmed to slowly ramp down in temperature until it is safe for the pieces inside to be in the outside air.

If you don't anneal the glass then you are producing a walking time-bomb: I knew someone who had had a paperweight for ten years, and then one sunny day it simply went off, exploding and spraying shards of glass all over his living room. Evidently it hadn't been annealed long enough for its size. Luckily, he wasn't home when it happened. And when I was blowing glass there were these things we made, terribly dangerous I realize now, called Prince Rupert's Drops:

"A kind of glass drop with a long tail, made by dropping melted glass into water. It is remarkable for bursting into fragments when the surface is scratched or the tail broken; -- so called from Prince Rupert, nephew of Charles I., by whom they were first brought to England." -Webster 1913

You can see one of these in the movie of Oscar and Lucinda, and there is a lovely bit in the book, though I can't find my copy to quote it. They are the ultimate in tightly-wound imperviousness, like some people: you can hit the leading end, the round end, with a hammer and nothing will happen; the hammer bounces off in this weird, almost disturbing way. But break the delicate tail, and the whole thing turns to powder in your hand. The internal stresses caused by instantaneous cooling balance the incredible surface tension, which makes the round part unbreakable. But the tail is a sort of long extension of the stresses, so that when it goes, the whole thing goes - with a sort of "phack!" sound.


I heard once that the large lenses mirrors they once used in observatory telescopes, which are often some fifteen feet across, had to be annealed for three to five years, they were so thick and large - or they would crack later and waste all the work, the casting and sanding and polishing, of making them. You can see why there were so few large telescopes in the ancient world: large lenses would be hard to produce, as the technology for annealing was much less accurate before the Industrial Revolution.

Glassblowing, that is, the insertion of a bubble into molten glass by means of a long tube, was begun in the first century BC in Roman Syria, and spread very quickly throughout the Roman world. Previously, everyone had been working on the Egyptian model of glass-making, which had been in use since around 1500 BC: glass was heated and wound around and around a core of mud or a small sand-bag at the end of a long pole. The effect, though colorful, was never large, and often faulty - not guaranteed leak-proof. As Wikipedia says, "this advancement transformed the material's usefulness from a time-consuming process...into a mass-producible material which could be quickly inflated into large, transparent, and leak-proof vessels."

Egyptian glass work

Glass is especially exceptional because it is difficult to classify as either a liquid or a solid. Unlike most solids it has no specific phase-transition, that is the specific moment when the physical properties change clearly from one phase (liquid) to another (solid). The transition from liquid to elastic solid to inelastic solid is a continuum; it has many of the properties of a supercooled liquid, but at room temperature. However, unlike a supercooled liquid, it doesn't move or behave like a liquid. There is an old story that glass continues to flow downward over time, which is why old windowpanes are thicker at the bottom, but this turns out to be untrue, sadly (I always liked the idea that my windows were actually a kind of slow liquid). The truth is likely that, because old ways of making pane glass had to do with pouring molten glass over a surface, the "poured spot" in the middle tended to be thicker. When it was cut up into pane-sized pieces, glaziers would simply put the thick side down, so it would be more stable. [wiki]

Neon jellyfish by Eric Ehlenberger

Another cool thing about glass is neon, or other gas-light tubes. Traditionally, "neon" signs are made by torchwork, i.e. bending glass tubes with the help of a torch, but more and more, people are creating beautiful works using various gasses and hot glass pieces. The trick is to evacuate the glass and provide an electrode at each end, so that the current has to pass through the gas from one electrode to the other, thus lighting it up. These devices, in the form of the Geissler tube, were first developed by a man named (yes, it's true) Heinrich Geissler, who invented them to demonstrate the principles of electrical discharge in 1857.

"They were mass produced from the 1880s as entertainment devices, with various spherical chambers and decorative serpentine paths formed into the glass tube. When the tube was handled (the terminals were insulated) the shape of the plasma changed. Some tubes were very elaborate and complex in shape and would contain chambers within an outer casing. If these were spun at high speed a visual disk of color was seen due to persistence of vision." [wiki]

The interesting thing about the Geissler tube/neon light is that it so quickly became a sort of ghettoized object. Neon, when most people think of it, carries a burden of '50s culture, of cheap hotels and sleazy bars, of flickering signs in Chinatown late at night. Ridley Scott used this shorthand to excellent effect in Blade Runner, but what more creative uses could it be put? What about architecture with vast, delicately-glowing arches of glass? What about Geissler tubes that occurred naturally, growing up inside of crystal structures? Or how about neon that followed the contours of natural objects, such as trees or rocks, in sinuous organic shapes, as part of the Queen's garden? I'd love to see that, somewhere.

Perhaps I'll put it in my next story, unless one of you do. I always wanted to make a hand-blown Geissler tube, probably with argon. Alas, keeping a full-on glassblowing studio is a pretty expensive hobby, and I'm afraid I traveled rather a lot instead. Sadly, too, it isn't like riding a bicycle: if you don't keep blowing, you lose the skill. But I don't ever forget the hot thrill of it...and I'm glad, in the long run, that I had the chance to explore something so innately magical, so surprisingly beautiful, and so, so, marvelously dangerous. It will always be there, in the back of my imagination.

* * * *

*(Editor's note: When I say "glassblowing", I am referring specifically to what is called "hot glass", rather than "flameworking". Flameworking is the small kind of glassblowing, starting with tubes or rods of glass and bending them or melting them to create beautiful objects. By hot glass I mean the working of larger amounts of glass that has been dipped out of a crucible full of molten glass. Both these kinds of glass-working can produce excellent results (or cheesy, depending on where you go, as I said above; beware the cheap ease of its shiny allure); but flameworking tends to be a solitary pursuit, in a small studio, and hot glass requires a large, noisy workspace with plenty of access to fresh air and loads of propane or other gas to run the equipment. It also requires more people to make it work.)

Other links:

Timelapse of Chihuly piece being set up

Great site for learning about glass

Pilchuck Glass School, where you can go to learn to make glass of all kinds: hot glass, flameworking, casting, kiln slumping, stained glass, Ravenna-style mosaics, you name it.

Also, try going to Youtube and typing in "pino signoretto" for a glimpse of a Venetian master glass sculptor at work.

3 comments:

spacedlaw said...

You have said previously that your French wasn't particularly good, so I would not expect you to pounce on it right now but if Bernard Tirtiaux's book "Le Passeur de Lumière" ever becomes translated into English, I strongly recommend you read it.
It is a haunting story about glass artists working on the cathedrals across Europe during the 12th century.
The writer is a master of glasswork (maitre verrier) and his way to describe the skill and the quest for new colours is magic.
As far as I can judge it only has been translated into Spanish thus far.

Jens Alfke said...

"the large lenses they once used in observatory telescopes, which are often some fifteen feet across"

I think you're referring to mirrors, not lenses. It proved impossible to make high-quality lenses larger than about 40 inches across, which is why since about 1900 all astronomical telescopes are the reflecting (not refracting) type.

Telescope mirrors are made from cylindrical "blanks" of glass, whose top surface is then slowly polished into a parabolic shape, then coated with silver. The backs of the blanks have a lot of hollowed-out space to reduce weight, but the glass is still very thick and I know it takes years to cast and polish them.

Even mirrors have hit practical size limits at about five meters, so new telescopes (like the Keck) are now built using an array of smaller mirrors, which are continuously adjusted by a computer to maintain a single focus.

(Thanks for the article! The Prince Rupert drops are amazing.)

Heather McDougal said...

You are absolutely right. I was taught by someone who was more interested in the casting than in the result, and on research, I find that indeed you are correct.

In fact, the Hale telescope (Mount Palomar, outside LA) mirror was more than 16 feet across. Later, blanks were cast in a rotating furnace (moving at 8 rpms) so as to get a more concave surface, to bring the annealing time down into the months instead of the years, and to avoid a lot of tedious grinding.

Thanks for the correction! And I'm glad you liked the entry.

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