What Is a Storm Glass and How Does It Work?

storm glass

A storm glass is a weather predicting device with crystal formations that supposedly change based on impending weather. However, can this device predict the weather accurately? We wanted to answer the most common questions surrounding storm glasses, and explain why it is likely that they do not work as well as some may claim.

What Is a Weather Predicting Storm Glass?

Storm glasses contain a mixture of chemicals which are said to crystallize in a way that makes it possible to predict the weather several days in advance, typically one to three days.

Admiral Robert Fitzroy

The storm glass was popularised by Admiral Robert Fitzroy

At the time that storm glasses first appeared (sometime in the 1700s), barometers—a reasonably accurate way to predict the future weather—remained relatively expensive. Most had to rely on cheaper methods of weather prediction, so sometime in the 17th Century an unknown inventor created the storm glass, but we don’t know why or how they did it. Storm glasses would eventually rise in popularity in the mid-1800s after British Naval Officer Admiral Robert Fitzroy used them aboard the HMS Beagle, which also happened to host a young Charles Darwin doing his initial research on evolution. This is why the storm glass is often called an Admiral Fitzroy Storm Glass.

Fitzroy was a weather enthusiast, and over the course of his expeditions, he examined the behavior of a storm glass to better understand how it worked. The relationship between the liquid’s behavior and the corresponding weather conditions used today derive from Fitzroy’s work aboard the Beagle.

Fitzroy became so enamored by the storm glass that he pushed for their use throughout the UK to help early meteorologists predict the weather better and more so after an 1859 storm which took many by surprise, resulting in hundreds of deaths at sea.

Storm glasses fell out of favor late in the 19th Century as mercury barometers became more affordable. These days, they have become little more than a conversation piece, and many may not even know that such a device ever existed.

How Does a Storm Glass Work?

Even today we do not entirely understand how these devices work, or how the crystals inside form and change shape. The truth is that there just haven’t been many studies done to figure out the process. The most common ingredients inside these devices include ethanol, distilled water, ammonium chloride, potassium nitrate, and camphor, although different storm glasses may have different combinations of these ingredients.

The version of the storm glass used in Fitzroy’s time was not completely sealed (typically by only a rubber cap) so pressure changes may have had some kind of effect. Today’s versions are hermetically sealed, which would likely mean the changes would have something to do with temperature differences outside the glass.

While research is slim on the storm glass (even when they were more commonly used), several studies over the years seem to suggest crystal growth is affected by temperature more than anything.

Is a Storm Glass Accurate?

These same tests also showed to be no better than a 50/50 chance of being correct, essentially leaving the predictions up to chance. Our opinion is that storm glasses should not be relied upon as a legitimate weather instrument but more of a conversation piece for your office or coffee table. If you’re looking for precise weather forecasts for your local area, invest in a home weather station instead.

Most home weather stations use barometric pressure to make predictions on weather conditions, over time barometric pressure has shown to be a much more accurate method of forecasting.

How to Read a Storm Glass

As we mentioned earlier, Robert Fitzroy popularized the current method to read a storm glass. Below is the chart used by Fitzroy and others to read a storm glass.

Storm Glass Liquid Appearance

Weather Forecast

Cloudy with small stars

Thunderstorms

Clear

Sunny and fair

Small, isolated stars during winter

Sunny and fair weather followed by snow in 1-2 days

Large, isolated flakes

Cloudy and humid, snow in the winter

Flakes which rise and stay in the upper part of tube

Winds in the atmosphere, changeable weather

Cloudy

Rain or rain soon

Strands forming near the top

Windy

Small floating spots

Fog

Crystals at the bottom

Frost

Does a Storm Glass Work Indoors? Here Is Where You Should Place It

Storm glasses are not intended for outdoor use, so if you purchase one, keep it indoors. They should also not be placed in a window that receives direct sunlight, or somewhere that may experience sudden temperatures changes during the day. Keep your storm glass away from walls facing the outside or near heating and cooling ducts.

How to Make a Storm Glass

Most of the chemicals used to produce the liquid inside of a storm glass are potentially hazardous. Inhalation of these chemicals could make you sick, and you should take care when handling any of the chemicals and prevent exposure to bare skin. We recommend that you buy one instead of making it yourself, especially considering many of the required chemicals can be difficult to obtain.

However, if you really want to make one, there is a way to do it. We recommend checking out the video below. You will need 100 proof vodka, camphor, potassium nitrate, and ammonium chloride. If you can obtain these materials, you’ll be able to make one on your own.

Be very careful and follow the video’s safety instructions to prevent any issues from occurring.

Weather Predicting Storm Glass Reviews: The Best Storm Glass to Buy

If making your own seems too dangerous, or you can’t obtain the materials necessary, then we’d personally recommend the Amymami Storm Glass on Amazon. This teardrop-shaped storm glass has received solid reviews across the board, although as we’ve mentioned above, don’t expect the predictions to be accurate.

Click here to buy the Amymami teardrop-shaped storm glass on Amazon

However, if you keep all of this in mind, and are a weather enthusiast (or know somebody who is), a storm glass will be a great conversation piece or gift. For more great weather-related gift ideas, take a look at our list of the best gifts for weather geeks.

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