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!

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42 Discussions


1 year ago

NightHawkInLight is correct that a storm glass is driven by temperature but the size and habit of the crystals is also affected by the rate of change of temperature. Tiny snow flake like crystals occur when the temperature falls rapidly. Larger fern like crystals form when the temperature drops slowly. If the temperature raises quickly smaller crystals dissolve fist. If the temperature raises slowly all the crystals dissolve and lots of clear liquid is visible.
So it is best just outside a bedroom window to tell you what happened during the early morning and will give you some idea of the way the day is heading.
Don't be afraid to experiment a little with the ingredients, if during the course of a year the storm glass is nearly always clear in your climate add a little more of the solid ingredients. If it is always a solid mass of crystals add more of the 100 proof spirit. Keep track of your proportions so you can make one for your friends when they want one.
From a health and safety point of view be aware: Potassium nitrate is a powerful oxidizer and both the alcohol and the camphor are flammable and the camphor fumes are a bit of health a hazard. (read up Wikapedia before using unfamiliar compounds).


1 year ago

Truly beautiful phenomenons. Thanks for sharing, having access to a chemical lab I might make one myself!


Hey! awesome intractable! I followed it your original a while back and it turned out great... Made another one tonight but ended up with some white stuff that would not dissolve and just kept floating on the surface in bits. I scooped them out and let the mixture do it's thing and it's now cooling so we'll see if it was a success or not. :) Any ideas what the floating bits were (I should have taken pictures but, you know... the smell of camphor had me not thinking right...)

7 replies

Hey! So, I had messed up the proportions as I was making a larger volume and had 94% ALCOOL (couldn't get the 100 proof). The 94% + 6% and then the remaining water got me all messed up. So last nights batch didn't work but I've just tried to correct it and confident I rectified the math and mixture... however, I ran into the issue with the impurities again. This time I snapped the attached 2 pics... the storm glasses are settling and I've got my fingers crossed... let me know if you know what the pictures are showing. They were mailable in the simmering potion but turned solid moments after I removed them where they became mostly brittle. Right now my storm glasses are simply cloudy and not looking like they'll get stormy. ....... we'll see.
Ps. I can't seem to upload pics on a mobile.

Your problem might be that your getting mixed up between 'Proof' and %Alcohol. These are not the same thing, it is also depends on whether you are in the UK or the US.



Hope this helps somewhat.

Hey! It actually did work out once I corrected the ratios. Only issue was all the impurities but I managed to scoop them out prior to bottling the liquid. :). On the plus side, because I had to add more stuff to even out the ratios, I ended up with a lot of liquid so I bottled it in numerous jars and am giving them out as gifts.

Are you using rubbing alcohol instead of drinking alcohol? I haven't tried rubbing alcohol, not sure if that works or not

No, it's drinking alcohol.
Here's a list of the things I actually purchased ( besides the camphor and distilled water):

The storm glass is still pure closet liquid. :(


2 years ago

Definitely going to try this. I have several interesting bottles that will be put to a good use this way. However, I'd love it if the quantities weren't in the metric system. It would be great to have the ml and grams in ounces or some other measure to match the devices I have on hand. The conversions are expressed in decimals and don't come out even. Is the resulting slight variance critical?

9 replies

Reply 2 years ago

You will need to weigh the ingredients with a scale, preferably a digital scale, anyway. Most digital scales, even a $15 one like the one I have, can weigh metric quantities. Why complicate things for yourself by converting to SAE units, with messy fractions, when it is easier to just use metric units as given?


Reply 2 years ago

Because I have absolutely no metric measurement devices or a digital scale.


Reply 1 year ago

Then how are you measuring the dry chemical quantities? You need a scale. They're only $10-$15.


Reply 2 years ago

gram convertion does not necessarily need a scale - 1 tsp equals 5 grams fyi


Reply 2 years ago

it doesn't matter incrementally - essentially the two salt compounds adhere to the camphor that give it it's crystal like structure.

horsenationMark 42

Reply 2 years ago

Thanks for the comment, but I have a dozen converters. That isn't the issue. Please read my original comment.

Nova_FreakMark 42

Reply 2 years ago

Thanks now all I need is a Windows computer. :D