Introduction: Fitzroy Storm Glass (18th Century Weather Prediction Device)

About: I like turning boring things into awesome things! Usually on video.

A storm glass is an 18th century weather prediction device made famous by Admiral Fitzroy, captain of the H.M.S. Beagle. You may recognize that ship name as the same one that Charles Darwin voyaged on. At the same time that Darwin was recording his biological findings, Fitzroy was recording his observations of the Storm Glass.

Be sure to watch the embedded video above to see a storm glass in action!

A storm glass is read as follows, from an excerpt in Pharmaceutical Formulas by Peter MacEwan in 1908:

Clear liquid : Bright weather.
Crystals at bottom : Thick air, frost in winter.
Dim liquid with small stars : Thunderstorms.
Large flakes : Heavy air, overcast sky, snow in winter.
Threads in upper portion of liquid : Windy weather.
Small dots : Damp weather, fog.
Rising flakes which remain high : Wind in the upper air regions.
Small stars : In winter on bright, sunny days, snow in one or two days.
The higher the crystals rise in the glass tube in winter the colder it will be.

In reality the changes that occur within a storm glass are purely reliant on temperature so it's accuracy as a forecasting device is suspect. My purpose for making one was mostly decorative and out of an interest in it's history. The display the glass produces when it first cools is very beautiful, as are the formations that slowly grow over time.


*This recipe can be scaled up or down depending on the size of the glass desired.

  • 900ml of 100 proof vodka (or 900ml of a 50/50 mixture of water and ethanol)
  • 85g camphor
  • 30g potassium nitrate
  • 30g ammonium chloride

Step 1: Preparing the Solution

The ingredients of a storm glass consist of three solid chemicals dissolved in a solution of ethanol and water. If you would prefer, denatured alcohol and distilled water can be purchased separately and mixed to a 50/50 ratio to act as the solvent in the storm glass. I find it simpler to use 100 proof vodka, which is already mixed and ready to use.

900ml of this ethanol/water mixture is added to a sauce pan, followed by 85g of camphor (this just so happens to be equivalent to 3 of the tablet packs it's sold in) and 30g each of potassium nitrate and ammonium chloride.

The pan is then set on low heat to allow the ingredients to more readily dissolve. To prevent the alcohol from evaporating a lid should be kept on the pan as it's heated.

Step 2: Filling the Glass

In about 10 minutes of heating everything should be dissolved in the pan and it's ready to be poured into the final container. Any glass bottle or jar will do. I liked the look of a square tequila bottle.

It's possible that the liquids will separate into multiple layers rather than fully mixing. That's nothing to worry about, the storm glass will still work. The top layer may freeze over like ice above a lake before other crystals start forming below.

Step 3: Using and Reheating the Storm Glass

As the bottle first cools it puts on a spectacular show, making it very easy to see where the idea that it could predict the weather came from. Often fog will first rise from the bottom of the glass and then give way to flakes of snow falling from it like a cloud. This initial display only happens when the glass cools off from an elevated temperature. The crystal formation that occurs day to day is much slower. It's this slow day to day change that is supposedly able to give weather predictions.

For best results the storm glass should be placed on a window sill or even outdoors where it will experience the most drastic temperature swings. With every temperature change the crystals will vary in their solubility, which is how the glass displays new crystal formations day to day.

If you would like to see the rapid crystal formation over again the glass can be reheated by removing any cork or stopper and replacing it with foil while the crystals dissolve. Once the liquid is again clear the stopper can be replaced and the storm clouds and blizzard will form all over again as the bottle cools.

Once again,here is the video tutorial with footage of a storm glass in action!

Thanks for reading!

Brave the Elements 2016

Runner Up in the
Brave the Elements 2016

Epilog Contest 8

Participated in the
Epilog Contest 8