Bottle Cutting

By Sean Michael Ragan
Category: Home, Electronics
Time Required: 30 minutes
Difficulty: Moderate

There are lots of ways to do this particular trick. You may have seen bottles “cut” using a bucket of ice water, a string soaked in fuel and set alight, a hot narrow gauge resistive wire, or some combination of the above. I’ve tried all of these ways, at one point or another, with varying degrees of success, and I’m reporting here the method that gives most consistent results for me. But if you’re interested in trying some other way, by all means experiment. Glass bottles are freely available just about everywhere, and you can always recycle your mistakes.

Regardless of which of these methods you favor, “bottle cutting” is generally a misnomer, as what’s really going on is a process of controlled breakage. (Unless, of course, you’re actually using a tile saw or something similar, in which case I’m prepared to agree it’s really “cutting.”)

Anyway. Glass, molecularly, is mostly silicon dioxide, but it’s distinct from crystalline solids like ice or table salt in that the molecules are not well-ordered in space. You may have heard some balderdash about how glass is really a liquid with practically infinite viscosity; generally the swelling of ancient cathedral windows at the bottom is cited as evidence to that effect. Well, it’s not true: There is, to my knowledge, no reliable evidence that glass will flow at room temperature regardless of how long you wait. Turns out cathedral glaziers made their windows thicker at the bottom on purpose.

But as an analogy, “infinitely viscous liquid” is not a bad way to understand the random molecular ordering of bulk glass. The upshot of this anisotropy is that glass does not cleave in orderly ways: Cracks tend to wander off in random, unpredictable directions, and shattering can easily occur due to internal stresses. There is, therefor, an element of luck involved in the bottle cutting operation, but with a bit of practice and good technique you can make it work most of the time.

Steps

Step #1: Select a bottle.

Your choice of bottle depends on what you want to do with the finished piece. Are you making a drinking vessel? A flower pot? A lampshade? Very often people are interested in cutting a particular bottle that has unique aesthetic or sentimental appeal. A special bottle of booze or wine, well-cut to make a useful container, can make a great gift for the person you shared it with.
Before you attempt to cut a valuable bottle, however, you should develop skill with bottles that are disposable to you. You will almost certainly ruin a few getting the hang of the process.

Conclusion

I have found that the use of a turntable during the heating process makes a significant difference. Attempting to manually rotate the bottle never works so well for me, but if I use a turntable the breaking process is quite reliable. The turntable I use is the bottom part of a cheap plastic rotating shelf intended to keep spices in the kitchen cupboard.

If you want a neater polished edge, you can use a series of grits of increasing fineness to do the lapping. A recharge kit for a rock polisher can be a good source for these. If you want to go this way, proceed (obviously), from larger to smaller grit, clean the edge thoroughly between steps, and be certain to use a separate lapping plate for each grit. Contamination of finer with larger grits can spoil the polishing effect.

The physical details of the bottle you choose to cut can also make a big difference. Generally, straight-sided bottles are easier to score evenly than those with round or sloping sides, so you may want to limit yourself to those at first. Many bottles have features I call "useful inclusions," which are rings or grooves molded in around the bottle's circumference. These are handy for two reasons: 1) Siting a cut at such an inclusion generally results in a better-looking finished piece, and 2) the inclusion itself can be used to guide a manual glasscutting wheel, eliminating the need for a bottle-cutting jig.

How the bottle is labeled can be important. I personally prefer bottles with painted-on labels, like Corona bottles, because the markings will stand up to wear, water, and washing over time and will continue to show off the origins of the piece throughout its lifetime. Or you can simply remove the labels altogether. Paper labels are generally the toughest to clean off; and the best tool I've found for this process is the wire wheel on a bench grinder. Even so, you may have to wipe off the remaining glue using Goo-Gone and/or lighter fluid.

If you plan to etch your bottle in some way, it is possible to use the label as a built-in resist. Just cut the design you want etched into the label, peel off the positive areas, and apply etching cream as usual. Adhesive plastic labels work best for this process; paper ones will result in messy edges where the etching cream bleeds under. When the etch is complete, just remove the remaining label as you normally would.