Glass is Weird

by Shardul, 27 Dec 2019

This semester, I was lucky to get into MIT’s beginner glassblowing class, described as “the single most over-subscribed activity at MIT” because there are over 300 students vying for 20 randomly-selected spots. Their lottery system makes you n times more likely to get in if this is your nth attempt (compared to a first-time entrant), so I was surprised to be picked the second term I tried, to the despair of some of my older friends who’d watched many excited faces get in for seven semesters, but never their own… (On the other hand, a friend told me that her name was the first pick in her freshman fall. “I was like, that’s it, I’ve exhausted my good luck for all four years at MIT.”)

Glassblowing is a difficult art. By the end of the class I was able to make pieces like these (with guidance from the instructors):

They look like normal glass objects! A success, because many of my earlier works were misshapen creatures whose best function would be as a paperweight. (Although I did make an actual paperweight too, pictured.)

Before coming to MIT, I’d never been interested in “maker”-y things, apart from playing around with digital electronics (but that mainly came from my interest in understanding logic circuits and programming microcontrollers). The Glass Lab was my first true maker experience. I never imagined myself in MIT’s lower dungeons, with my sleeves rolled up, sweating beside a 2000 °C furnace as I squeezed molten glass into practical shapes—but I guess MIT seeps into you like that after a few semesters.

I won’t try to explain the process of glassblowing because (i) I’m sure it’s been explained better elsewhere by someone who knows what they’re doing and (ii) I quickly realized that it’s very hard to explain physical processes like blowing glass without visuals (actual lab space, or videos, or making funny hand shapes, etc., none of which are particularly suited to a blog post). But one my main takeaways from the class was that glass is weird. Glass is counter-intuitive. It is unlike any substance you deal with in ordinary life and it makes your cognitive physics engines sputter and choke, until (ah the wonders of the brain) you relearn how glass behaves as a fluid through direct experience.

Picture this: you reach into the furnace and pick up a glob of molten glass on the end of a pipe. It’s not a dip or a swirl but rather, you rotate the pipe to make glass catch on to it (because it’s a very viscous fluid); the faster you rotate, the more glass you can pick up, but if you rotate too fast then centrifugal force will turn your glob of glass into a hard-to-work-with mushroom instead of the more ideal egg shape.

Now you’re bringing the pipe out of the furnace but oops, you drag along a thin trail of glass, like the trail from honey. It sticks to the sill and… instantly becomes a solid wire that you can snap off with your foot. (It’s still hot, but not molten, because it cools very fast with a large surface area but small mass.) Similarly, if you hold the pipe straight down, glass will droop off the end and make a puddle on the floor… which can be lifted straight back up as a slightly soft, puddle-shaped piece of glass with a very flat bottom. (Do not try this at home because the lab floor is specially made to handle these high amounts of heat. (I don’t know why you’d be trying glassblowing at home anyway.)) Touching metal tools to glass also dramatically cools it and makes it change its properties faster than you’d expect. However, the most extreme example of cooling would be the process known as “breaking off”: when you want to take your work off the pipe, you make a constriction where you want it to break and then pour a few drops of water at the joint, delivering a thermal shock that produces many small cracks going through the joint. At this point, giving a sharp tap to the pipe makes the piece fall off.

Let’s try heating. If you have a blown-out glass surface surrounding a hollow interior, as expected, it heats up quicker than solid glass. This can be problematic if you heat a thin surface too much, as it starts becoming more fluid until… surface tension pulls the surface in and it begins to fold and/or scrunch up like a plastic bottle when you suck the air out. This totally freaked me out the first time I saw it. Sadly I don’t have a picture of my own, although this is something close I found online. Sometimes, you can use this to your advantage, for example by making the lip of a bowl extremely hot and then giving your pipe a good downwards flick to create a perfectly symmetric “handkerchief” ripple. But these surface features and other texture details tend to smooth out if you’re not careful to limit the heat.

Speaking of thin surfaces, a mishap we were warned against was blowing a surface too thin to the point where it turns into wispy cellophane-like pieces, floats into the air, and gives you a good deal of respiratory trouble. If I had pictures for this one I’m not sure I’d be able to share them.

Lastly, tool usage. Most of the tools we used were straightforward: tweezers can grab and lengthen the piece, or draw out bumps/wires, or make dents; the jacks can constrict and expand sections of the piece; wet wooden paddles and blocks can shape the piece, sizzling on contact with the glass but not burning. Shears on the other hand can cut through glass with a satisfying soft crunch! (It’s surprisingly more satisfying than cutting through paper.) It has to be just the right temperature and you have to work fast to keep it that way, as too high means the glass just sticks to the shears in blobs and too low means it’s too solid to work at all.

I now see why the Glass Lab is under the materials science department. There’s much more to glass than just the craftsmanship and glassblowing-as-art: glass is a very interesting material that humans have been exploring for many centuries in various forms. Everything I described above was just basic observations about standard transparent glass, and things get complex when you work with colors, patterned sheets, pieces assembled from separate parts, … talking to the instructors it was clear that they’d developed detailed intuitions about what you can do with glass and how, that were just as much scientific as artistic.

A parting note: perhaps what’s weirder than glass is the annual MIT glass pumpkin sale, called The Great Glass Pumpkin Patch. At face value this sounds like a very normal thing. Glass lab students and instructors make glass pumpkins by hand (see the link for pictures), put them on display, visitors purchase them. Reading the description, however, you notice that “Saturday morning line-placeholder ticket distribution begins when the lab director arrives (usually around 6 AM)” and “Proceeds from the MIT Great Glass Pumpkin Patch cover 100% of the annual operating expenses of the MIT Glass Lab”. A little strange, isn’t it, that the distribution of tickets that mark your place in line to enter the exhibition starts around 6 AM on a Saturday, and sales from the event cover the entire year’s expenses of the lab, given that renting time in a similar glass lab is usually $50 or more per hour?

According to a friend of mine who went last year, the truth is that the event is stuffed with extremely rich and obnoxious parents, spouses, etc. of MIT affiliates, who start lining up well before 4 AM to enter the Pumpkin Patch. Their sole aim is to be the first to rush in and buy a handful of the most ridiculously expensive pumpkins (several hundred dollars each) regardless of the actual aesthetics of the piece. They bicker over their position in line; they get upset when someone else takes a piece they were eyeing; they casually mention, “Oh, I have twenty of these at home, this will be a perfect addition to my collection”. My friend couldn’t make sense of it and neither can I. I guess it’s some consolation that if I ever make a glass pumpkin, no matter how it turns out (perhaps I’ll have to rename it as a decorative gourd?), I could get a little extra cash from a benevolent patron.