Storm Glass Weather Predictor: How They Work, How to Read Them & Where to Get One

By Matt, storm glass maker since 2017.

Last updated 5/16/26

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I’ve been hand-making storm glass since 2017. In that time I’ve mixed hundreds of batches, watched crystals form in just about every weather pattern the Northeast can throw at a window, and shipped them to customers in every climate from Phoenix to Reykjavik.

This page is everything I’ve learned about how storm glass actually behaves, how to read it, and what to look for if you want to buy one that isn’t junk.

Why I Started Making Storm Glass

 

 

I first ran into a storm glass in an old maritime museum gift shop and couldn’t stop thinking about it for weeks. A sealed glass tube with crystals that grow, shrink, and rearrange themselves on the windowsill? That’s the kind of object that makes a room more interesting just by sitting in it.

When I went to buy one, every option online was either a cheap mass-produced novelty or a $200 antique. Nothing in between. So I started mixing my own.

After a lot of failed batches (too much camphor cracks the seal, too little and you get no crystals at all), I dialed in a formula that gives consistent, beautiful crystal formations. Now I sell them on Etsy and ship them out one at a time.

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Storm Glass Quick Comparison: What People Buy Them For

Use Case	Best Size	Where to Place It	What You’ll Notice
Gift / Decor	Standard	Bookshelf, mantel, desk	Crystal patterns shift over days
Weather Watching	Larger	Near a window (north-facing ideal)	Faster reaction to outdoor temperature swings
Sailing / Maritime Lover	Standard or large	Anywhere visible	Same kind of object Admiral FitzRoy issued to fishing fleets
Classroom / Curious Kid	Standard	Near a window with daily sun	Great for observation journals
Meditation / Focus Object	Either	Desk or nightstand	Slow visual change, calming to watch

What Is a Storm Glass?

A storm glass is a sealed glass vessel filled with a clear liquid mixture that forms crystals in response to temperature changes. The liquid is a blend of distilled water, ethanol, potassium nitrate, ammonium chloride, and camphor. As conditions around the glass change, the crystals dissolve, regrow, sink, float, or branch into feather-like shapes.

It was popularized in the 1860s by Admiral Robert FitzRoy, a British naval officer, meteorologist, and the captain of HMS Beagle (the same ship Darwin sailed on). FitzRoy distributed storm glasses to fishing communities along the British coast, believing they could give sailors a heads-up about incoming storms.

Modern meteorology has since shown that storm glasses primarily respond to temperature, not the more complex variables like atmospheric pressure or humidity that actually drive weather. But they’re still a fascinating window into 19th-century science — and they’re genuinely beautiful to watch.

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How Does a Storm Glass Actually Work?

Here’s the short version: the chemicals inside have different solubility curves at different temperatures. When it gets colder, some compounds drop out of solution and form crystals. When it warms back up, those crystals redissolve. The shape, location, and density of the crystals shift based on how fast and how far the temperature moves.

What I’ve noticed after years of watching my own pieces:

• Sudden cold snaps produce the most dramatic crystal growth — overnight you can go from a clear tube to a tube packed with feather-like blooms.
• Slow seasonal changes create denser, more solid crystal structures.
• Direct sunlight will mess with your readings. Place it on a windowsill that gets indirect light, or on an interior wall near a window.
• Heating vents will also throw it off. If your storm glass sits above a radiator it’ll stay clear no matter what’s happening outside.

The traditional belief is that storm glass predicts the weather. The honest answer is that it reacts to weather — specifically to temperature, which is one piece of the weather puzzle. You’re not going to outforecast your phone, but you will get a beautiful visual record of how the temperature in your home is shifting.

How to Read a Storm Glass

This is the part most pages get wrong. They list crystal shapes as if they’re a strict code, but in reality you’re looking for changes more than absolute states. Here’s how I tell people to read theirs:

Look at what’s different from yesterday. If the tube was clear last night and there are feathery crystals at the top this morning, the temperature dropped — and probably a cold front rolled through.

Crystal location matters.

• Crystals at the top: colder weather, possible cold front incoming
• Crystals sinking to the bottom: warming trend, settling weather
• Crystals throughout the liquid: rapid temperature change, often before unsettled weather

Crystal shape gives you clues.

• Clear liquid: stable, fair conditions
• Cloudy or hazy liquid: humid or overcast
• Small dots or specks: foggy, humid weather
• Cloudy liquid with small stars: traditionally associated with thunderstorms
• Snowflake-shaped crystals: cold temperatures, possible snow
• Feather-like or fern crystals: windy, breezy conditions
• Large crystals at the bottom: dry, clear weather

Give it time to settle. If you just moved your storm glass from a cold porch to a warm living room, wait 24–48 hours before reading anything into the crystals. They need time to equilibrate.

Storm Glass Quick Reference Table

What You See	What It Means
Clear liquid	Stable, fair weather
Cloudy liquid	Cloudy or rainy conditions
Small dots in liquid	Foggy or humid weather
Cloudy with small stars	Thunderstorms possible
Crystals at the top	Cold front, dropping temperatures
Snowflake-shaped crystals	Cold weather, possible snow
Feather-like crystals	Windy or breezy
Large crystals at bottom	Dry, clear weather ahead
Crystals dissolving	Warming trend

Where to Put Your Storm Glass

This is the single biggest mistake new owners make. Placement determines whether your storm glass does anything interesting at all.

Best spots:

• A windowsill that gets indirect light (north-facing is ideal)
• An interior wall near a window — close enough to feel temperature swings, far enough to avoid direct sun
• An entryway or mudroom that reflects outdoor conditions

Spots to avoid:

• Direct sunlight (heats the liquid above what’s happening outside)
• Above or near heating vents and radiators
• Next to a fireplace
• In a bathroom (humidity from showers can affect the seal over time)
• In a sealed-up, climate-controlled office with no temperature variation — the glass needs some change to do its thing

Storm Glass Buying Guide: What to Look For

Since I make these myself, here’s what I’d tell anyone shopping for one:

Look at the seal. A poorly sealed storm glass will evaporate within months. You want a hand-sealed top with no visible air gap. Mass-produced versions often have plastic caps that fail.

Check the liquid clarity. When you receive it (or look at product photos), the liquid should be crystal clear. Cloudiness right out of the box means the formula wasn’t mixed properly.

Size matters for visibility. Smaller storm glasses are charming but the crystal formations are harder to see. If you want a piece you’ll actually watch, go larger.

Avoid plastic. Some cheap “storm glasses” use plastic vessels. Glass is non-negotiable — plastic interacts with the camphor and ethanol over time.

Buy from someone who makes them. A maker can answer questions, replace a broken piece, and stand behind the formula. Drop-shipped versions on Amazon often have no support and no quality control.

Frequently Asked Questions About Storm Glass

Does a storm glass really predict weather?

Not in the way modern forecasting does. A storm glass reacts to temperature changes, which correlate loosely with weather patterns. It’s a beautiful historical curiosity and a fun observational tool — not a substitute for your weather app.

How long does a storm glass last?

A well-made, properly sealed storm glass can last decades. Mine are designed to last a lifetime if the seal stays intact and they aren’t exposed to extreme heat. Cheap mass-produced ones often fail within a year or two.

Is the liquid inside dangerous?

The liquid contains ethanol, camphor, potassium nitrate, and ammonium chloride. It’s sealed inside the glass and isn’t dangerous to have around as long as the glass stays intact. Keep it out of reach of small children, just like you would any glass decor item with chemicals inside. If one breaks, ventilate the room and clean up with gloves.

Why aren’t my storm glass crystals changing?

Three usual culprits: it’s in a temperature-stable room, it’s near a heat source, or it’s in direct sunlight. Move it to a windowsill with indirect light and give it a few days. You should see noticeable changes with any meaningful temperature swing.

Can I make my own storm glass?

You can — the formula is well documented online — but getting consistent, beautiful crystal formations takes a lot of trial and error. Sealing the glass properly without trapping air or losing ethanol is the trickiest part. I went through dozens of failed batches before I got mine right.

Did Admiral FitzRoy invent the storm glass?

He popularized it but didn’t invent it. Storm glasses existed earlier in various forms — alchemists and natural philosophers had been experimenting with similar mixtures for years. FitzRoy’s contribution was distributing them widely and publishing instructions for reading them, which is why his name is attached to the device today.

What’s the difference between a storm glass and a Galileo thermometer?

A Galileo thermometer uses floating glass spheres with different densities to indicate temperature. A storm glass uses dissolved chemicals that crystallize at different temperatures. Both are decorative scientific instruments, but they work on completely different principles.

Why I Still Love Storm Glass (Even Though It’s “Debunked”)

Here’s what gets lost in the science-vs-superstition conversation: storm glass is one of the few decorative objects in your home that actually does something. It changes. It reacts. It tells you, at a glance, that the world outside your window is different today than it was yesterday.

We’ve gotten so used to consuming the weather through screens that we’ve forgotten what it feels like to read it from the world around us. A storm glass on your windowsill puts you back in that loop — even if it’s only telling you part of the story.

That’s why I keep making them. Not because they’re going to replace your iPhone’s weather app, but because they’re a small, beautiful reminder that there used to be other ways of paying attention.

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