First Day - Glasswork

There'll be two posts today. The first is kind of a lesson on basic glassworking. The second is more-or-less storytelling.

Ok, so the lab in which I work requires ampouling of samples. This means making ampoules. Lots of them.

Source material: borosilicate glass tubing, 1 cm diameter (hey, metric!). The ones in the lab are almost as long as I am tall, which either says alot about the tubing or says alot about me. A hydrogen/oxygen torch is required, also. (A lighter to start the torch would be nice.)

1. Mark the tubing to the desired length (say 30 cm or so - about twice the ampoule length), as many as desired. It's probably more efficient to mark multiple tubes at a time.

2. Cut the glass. The lab I'm in happens to have an automated diamond-edged wheel. It basically spins so that I just have to touch the glass tubing to the wheel, slightly rotating the tubing, to get a deep scratch, about 1/5 - 1/4 the circumference of the tubing. My idea of a deep scratch is "just when the wheel breaks through one tubing wall". I like it - the manual kind strikes me as annoying*. There's a downside though - the wheel has been set up so that it turns toward the user, along with any accompanying shrapnel. Thus, the fume hood sash must be down (or some other form of protection set up).

3. Break the glass. Hold the tubing so that opposing thumbs meet diametrically across from the scratch (in particular, the scratch faces away from you). Break the tubing by applying a outward and slightly sideways force - like, I don't know, breaking a cookie. And do it gently! It will break more-or-less evenly, no worries there. Now we have a whole bunch of shorter glass tubing.

4. Now the fun part - torch! First check the gas source, both hydrogen and oxygen. Main valve is on, regulator is set correctly, pressure is good. Then open the regulator valve.

5. Start the hydrogen flow on the torch. Light it. It will burn mostly colourless, a little blue, a little pinkish-yellow. Sometimes flares yellow if the air's dusty or something. Adjust the hydrogen until the flame length is about umm, the distance between a stretched thumb and forefinger. If I have to give a number I'd say 15 cm.
Then start the oxygen. The flame will turn very bright, and a lovely pale blue. Adjust oxygen flow until the flame is well-defined (it looks kind of like a pencil), and about oh, a little longer than twice as long or so.

6. At this point I change safety glasses from the normal ones to ones that block UV. It's probably safer to do this earlier, but I can't see the hydrogen-only flame with the glasses on!

7. Hopefully the cut tubing have been stacked somewhere safe and reachable without touching the torch. Pick one, and heat the middle, rotating constantly (a moderate speed is fine). The hot part will turn white. Don't touch the cut ends - they are sharp and hot. When you feel the glass starting to sag around the white part, remove the tubing from heat and pull. Hard. Now you'll have something that looks like two Pasteur pipettes stuck tip-to-tip. Disconnect them by heating the very thin middle lightly and pull a bit more.

Incidentally, two things to note: always rotate when heating the glass. Never pull and heat at the same time. Failure to comply will give wrecky results.

8. To turn "Pasteur pipettes" into ampoules, heat the part of each "pipette" where it starts to thin down drastically. With rotation, of course. I'm right handed, so the large end is in my right hand (and does all the rotating in this step), and the smaller end is in my left hand. When the thing softens, pull the thin part off entirely. That thin end might make a good TLC spotter...

9. Seal the end of the tubing by keeping the end (and only the end) in the flame with constant rotation. It should seal, and flatten out. If it doesn't flatten, remove from heat, quickly press on a heatproof surface (I use the torch), and return the end to heat.

10. For people who likes round ends (like test tubes), blow through the cold end of the tube. Assuming that the hot end is hot enough, the flat part will round out. Don't touch the diamond-wheel-cut part; it's still hot and sharp.

11. Fire-polish the open end by heating it (with rotation) just until the entire circumference of the open circle turns white (i.e. glass has melted).

12. Turn off the torch. Oxygen off first, always. Then hydrogen. (Try doing it the other way once - see why this is necessary.) Then all the other valves off. Chuck the useless glass bits into the glass disposal bin, or donate them to organic chemists, whatever.

And yea. Two open-ended ampoules. Not clean, mind you. I'll post on how to close the other end when I learn how, though I don't see why it should be any different from making the ampoule in the first place.

*Caveat: I've never used a manual glass tubing cutter, but I've used one for cutting metal tubing. For metal tubing cutters, don't just scratch the tubing - cut right through with it. Metals are too flexible to snap.