Geek romance: How to make a Storm Glass pendant

Toward the end of last year, being in possession of two novelties - a girlfriend and a steady job - I decided to spend my free evenings crafting a very special piece of jewellery. I was inspired by a visit to Barometer World in the late summer, where I discovered the curious material known as storm glass (tragic backstory recounted here).

In short, a storm glass is a weather divination tool so old that nobody really knows where they came from. It's likely they were borne out of alchemy experiments performed during the medieval period. Inside a sealed glass tube, crystals bloom, wither and vanish spontaneously, apparently spurred on by weather fronts. It was a thing of wondrous beauty.

Nobody knows what exactly makes storm glasses act this way. I've read in many places since that it is pressure changes, as with a barometer. This clearly isn't true, as the fluid is sealed inside a solid glass chamber. Others cite temperature fluctuations - far more probable - or, more exotically, electrical discharge across the glass (again, unlikely, glass is a very fine electrical insulator). Even spooky quantum forces get a mention.

It was around then that an idea hatched in my head: if it was really heat that caused a storm glass to sigh and sway from one condition to another, then why couldn't it be turned into a pendant? One that would react to the body heat of the wearer? I would make a storm glass - not one that predicted the passing of nature's cold fronts, but one that signalled the tempests of the heart! A crystal that would melt in the heat of my girlfriend's passions, and grow hard in the cooling of her mood. It would be easy, right?

The recipe for storm glass can be found almost anywhere, although a slightly different version exists for warmer climes, hinting at where I would need to go. It contains only five chemicals: water, ethanol, camphor, potassium nitrate and ammonium chloride. Without access to a lab, some of the chemicals can be quite tricky to get. Don't believe anyone who tells you that chemists will stock these. If you want to find a pharmacist that will sell you potassium nitrate, you'll have to go to one in the 1960s. Probably because pretty much every one of the ingredients can be used in a bomb. Thankfully, capitalism and the internet conspire, and you can find all the ingredients in discrete quantities on Amazon.

I'm not going to get into the practicalities of making genuine storm glass, as there are several good videos on YouTube that you can follow. But here's where the normal storm glass, and a romantic storm glass pendant differ.

Camphor is quite soluble in alcohol, but not at all in water. Similarly, potassium nitrate and ammonium chloride dissolve far better in water than alcohol. So the whole lot is like three fat men struggling to perch on a single bar stool. It's this inherent instability that makes the storm glass sensitive to small fluctuations in the environment.

The solution produces two different crystals: cloudy snowy ones that are the camphor. They are big and fluffy and suspend in solution quite well. The other solids crystalise into far more beautiful, spiky or feathery frost-like crystals. These, however, do not suspend in solution, and sink to the bottom. A badly-made storm glass separates out:

The traditional recipe is unsuitable for a storm glass pendant for two reasons: One, it is primed for an outdoor barometer, so functions at 10 to 15 degrees C. My storm glass of the heart will sit next to my girl's skin, and be a lot warmer. Wearing normal storm glass at this temperature renders it clear, so firstly you need to increase the concentration of the ammonium chloride and potassium nitrate. Basically, warm up your water to skin temperature, and keep adding those chemicals until the solution is saturated. Add the saturated solution to your camphor-alcohol mix. Personally, I think the amount of camphor in the traditional recipe is grossly over-stated (most of my early glasses came out over-fogged), so there's no need to add more - in fact, you may need to add a little (A LITTLE) alcohol to your storm glass to clear out the stubborn camphor crystals. In short, it's a lot of tweaking, sealing, wearing, testing, retweaking... and so forth.

Put the mixture in a small vial - I bought mine here. Small vials help keep the crystals suspended, but even so, this one, like many, many others, was rejected:

Eventually, you'll have a glass that is almost clear when warm, and produces beautiful crystals. I've seen snowflakes, clusters, clouds, fog, frost, and delicate crystal ferns grow inside my storm glass. It's run the entire gamut from clear to pearlescent to quartz. And best of all, it seems to work whilst hanging around the neck of my belle. Unfortunately, it's very tricky to photograph, especially after you give it away, but here's a try:

If you pull this off, expect brownie points aplenty from any self-respecting nerd girl, and give yourself a well-deserved pat on the back!

Now, before the inevitable requests: yes, I still have lots of storm glass fluid left over. And yes, I have several empty vials. But no, I will not make you a storm glass. I will not sell you one. Sadly, I can not even give any storm glass pendants away, or trade them for other curios, as I planned. My #1 nerd has forbidden it. She won't play dice with the idea of another woman walking around with my signature gift hanging from her neck. Proving once again that although I might know a lot about science, I have much to learn about a woman's heart.

Best of luck, chemistry lovers, you're on your own from here.