To grow Epsom salt crystals, prepare a solution of concentration 75 g / 100 mL. Wait for seed crystals to form, place them somewhere sheltered, and watch crystals grow within a week or two.
Hi, I’m Chase, and I love to grow crystals using household chemicals. In this article, I’ll show you guys how to grow big Epsom salt crystals at home.
Epsom salt is commonly used as a bath salt and for making beer. It is also known as magnesium sulfate heptahydrate and functions as an essential plant nutrient. You can find it at the pharmacy or a gardening store.
If you dissolve lots of Epsom salt in water and wait for the solution to evaporate, long transparent crystals will form. Generally speaking, they are the fastest growing of all common crystal growing compounds.
There are many guides on how to grow Epsom salt crystals online. The most common method is to prepare a saturated solution, put them in the fridge and wait for the crystals to grow overnight. But the crystals that form look like tiny needles – not impressive at all. I wanted huge, transparent crystals the size of my palm.
So, I spent 2 years experimenting with them, and I’ve finally come up with a reliable formula for anyone to grow big single crystals of Epsom salt at home.
Let’s get started.
Growing Epsom salt crystals
To grow these crystals, you’ll need:
- 1 kg of Epsom salt
- A weighing scale/electronic balance
- A large pot for heating water
- A spoon for stirring
- 2 jars, one big, one small
- Thread/nylon fishing line
- A pencil
Preparing the solutions
This is the most important step, which will determine both the shape of the crystals and how quickly they grow.
First, we need to prepare a saturated Epsom salt solution. A saturated solution is a solution that contains the maximum amount of dissolved salt. This part is tricky because different amounts of Epsom salt can dissolve in water of different temperatures – and the difference is big.
But don’t worry about it. Just follow these steps:
First, heat up some water in a pot.
Next, dissolve a bunch of Epsom salt into the hot water. I recommend preparing 1000 mL of saturated solution.
If your room temperature is 25°C, your solution should have a concentration of 75 g / 100 mL. If your temperature is different, refer to Table 1 below.
Note that this does not mean that you should dissolve 750 g of Epsom salt in 1000 mL of water. If you do this, you will end up with around 1300 mL of solution, which is not correct.
Instead, just dissolve 750 g of Epsom salt in around 500 mL of water (the exact volume of water is not important). The important thing is that everything gets dissolved.
The initial solution should be very cloudy. Keep stirring until all the grains of Epsom salt dissolve, causing the solution to turn clear. This should take no more than 5 minutes.
Close the lid and wait for the solution to cool down to room temperature.
While waiting, get a large jar, and using a marker, draw a line on the 1000 mL mark.
Then pour the solution into the jar. Since some of the water evaporated during heating, your solution should actually be around 750 mL, which is below the line that you just drew. Add more water to the jar until the level of the solution is exactly equal to the line.
Stir it around with a spoon to mix evenly.
And you’re done. This will be your saturated solution. Let’s call it solution A.
Set it aside for now.
We need to prepare a more concentrated solution to kick start the growing process. Let’s call this solution B. Using the exact same procedure as above, prepare a solution with the following concentration:
58 g / 100 mL
63 g / 100 mL
63 g / 100 mL
68 g / 100 mL
67 g / 100 mL
73 g / 100 mL
|71 g / 100 mL||78 g / 100 mL|
75 g / 100 mL
83 g / 100 mL
|30°C||80 g / 100 mL||
88 g / 100 mL
Table 1: Concentration of solutions
Unlike solution A, you don’t have to prepare so much solution B. Just 250 mL is enough.
Again, wait for solution B to cool. Make sure to cover the lid during the cooling process.
If you encounter any problems in this step, check out the troubleshooting section at the end of this article.
Here are my two solutions, side by side. I decided to pour my solutions into beakers so that I can demonstrate the crystallization process more clearly later on, but you can use any other jar you like.
Two solutions. I stored excess solution A to another jar that is not shown here.
Now, here comes the fun part.
Growing Epsom salt seed crystals
Sprinkle a few grains of Epsom salt into solution B. Stir the solution vigorously for 5 seconds.
Next, cut 20 cm of nylon fishing line, and tie one end to a stick. Poke the other end of the fishing line into solution B.
A bunch of crystalline dust will form:
This is because the solution at room temperature cannot dissolve so much Epsom salt, so the extra salt that you dissolved previously has to come out of solution, forming crystalline dust in the process.
Wait 5 to 15 minutes. The dust will quickly grow into crystals. Some of them will stick to the fishing line.
However, if you have waited for 30 minutes and still no crystals have formed, it means that your solution was not concentrated enough. Dissolve 5% more Epsom salt in the solution and try again.
On the other hand, if your solution is more supersaturated than mine, the crystals will grow faster and resemble needles:
Also, the longer you wait, the more crystals will form, and eventually the whole jar will be filled with crystals. We don’t want that to happen.
So, once a few crystals have formed on the line, we want to transfer it from solution B to solution A.
In the picture below, I have moved my seed crystals to solution A. This solution is less concentrated, which means that the crystals will grow slower. This is good news, because it creates the ideal conditions for growing big, transparent crystals.
You can see 3 different types of seed crystals here. The more saturated solution B is, the longer the crystals will be. If you wait further, more crystals will clump together to form a cluster.
Move this setup to a sheltered location with minimum air movement. Places like the inside of a cupboard, the basement or a storeroom work nicely. Also, partially cover the top of the jar with a lid, or some plastic wrap to slow further down evaporation.
These Epsom salt crystals will begin growing, and here’s what they look like after 3 days:
You might also notice some extra crystals have formed on the fishing line. Left alone, they might stick to your main crystals.
To remove them, lower the unwanted crystals into a bowl containing warm water. Crush them with your fingers to make them dissolve faster.
Growing huge Epsom salt crystals
We’ve now reached the easy part. All you have to do now is to wait, as the Epsom salt crystals get progressively larger.
Let’s focus on two of my single crystals, to see how they grow over time.
After one day:
After 3 days:
At this point, lots of smaller crystals will have formed at the bottom of the jar. They will compete with your main crystals and slow down their growth. But don’t bother trying to pick them out.
Instead, pour the solution into another jar, transfer your crystals there and continue growing. The leftover crystals at the bottom are very pure, and they can be recycled for future use.
You can remove the plastic wrap at the top of the jar now. The crystals should be big enough to handle the extra growth rate without getting cloudy.
After 10 days:
If the crystals start to outgrow the container, transfer them to a bigger jar filled with saturated solution.
If you don’t have enough solution, prepare more, using the recipe for solution A. Make sure that the solution cools down to room temperature before immersing the crystals.
Personally, I think it’s a hassle, so I prepare my saturated solutions in large batches. This way, I’ll always have some extra on hand.
After a month:
The Epsom salt crystals should be 7-9 cm long now, and weigh about 50 grams.
At the same time, I was also growing some crystal clusters. Here they are:
By now, the weight of the crystal should start to strain the fishing line. Don’t remove them from solution too often to take a look – the line might snap or slip out of the crystal. This happened to two of my crystals, and I had to stop growing them early.
I’ll show them later.
With no more competition, my remaining crystal grew quickly.
After a total of 2 months, it had gotten so long that it would no longer fit in my biggest jar. Therefore, I decided that it was time to harvest it.
To stop growing, dry the crystal on a piece of paper towel. Let the towel absorb excess solution, and tap it a few times to dry it.
There are 3 things you shouldn’t do:
- Wash the crystal. This will cause part of it to re-dissolve, making the edges less sharp.
- Place it on the paper towel for too long. The paper will stick there.
- Let the solution on the crystal to dry naturally. This will cause crust to form on its surface.
With that said, we’re done!
The results speak for themselves.
The biggest single crystal is 11.6 cm long and weighs 126 g. The next largest single crystal and the crystal cluster both weigh 50 g.
Enjoy your creations, and share them with your friends. If you’re doing it with your children, I’m sure they’ll find it amazing to grow their own gems.
Epsom salt crystals have water trapped inside their crystal structure. When heated, these crystals will lose the water inside and turn from transparent to white. Unfortunately, this also happens naturally if they are exposed to dry air.
Left: a normal crystal; Right: a dehydrated crystal. It was left out in the sun for a week, and looks like a piece of chalk.
If you live in a place with high humidity (>80%), Epsom salt crystals are completely shelf stable. However, if you live somewhere drier, the crystals might turn white over time. There are 2 ways you can prevent this:
- Coat them with a layer of transparent nail polish.
- Place them in an airtight container, together with some Epsom salt powder. The powder will maintain a stable environment inside the container which prevents your crystal from dehydrating.
Troubleshooting & FAQ
Generally, the only problem with growing these crystals is getting the concentration of the solution right. The tables I have provided above should be helpful.
If you face any problems, first make sure that your solution concentration is accurate. If it still doesn’t work, check the condition of your solution with the following method:
Drop a single grain of Epsom salt into the solution. Wait 1 hour.
- If the grain shrinks/becomes smaller, the solution is undersaturated. Reheat the solution and add 5% more Epsom salt.
- If the grain remains the same, the solution is exactly saturated. You can proceed with the growing process.
- If the grain grows slightly, the solution is slightly supersaturated. You can also proceed.
- If the needles form around the grain/throughout the solution, the solution is very supersaturated. Add 5% more water, reheat, and try again.
How can I make my crystals clearer?
The slower your crystals grow, the clearer they will be. I took a month to get my single crystals pictured above to 7-9 cm long. But you can actually grow them much faster.
Compare the clarity of the crystal on the top with the crystal on the bottom:
The top one took 1 month to grow. The bottom one, which is similar in size, took just 2 days to grow. As a result, its crystal structure contains lots of defects, causing it to be less transparent.
Slower growth also reduces the jaggedness at the tips of the crystals. But as far as I know, there is no way to prevent them entirely. It seems like it’s a characteristic of Epsom salt crystals. If you managed to grow crystals without them, please let me know.
How hard are Epsom salt crystals?
These crystals are surprisingly tough for home grown crystals. I had trouble trying to break a big crystal with a mortar and pestle, which means there’s no risk of breaking a crystal by accident, apart from dropping it, of course.
But they also dissolve slowly in water. This makes Epsom salt crystals unsuitable for making jewelry.
- You can add food coloring to dye the crystals. It works best for needles and clusters. Single crystals tend to exclude the dye, leaving only a slight tint.
- Solutions that are left for very long might form bits of mold. This is a slight problem and can be quickly solved by filtering the solution.
- The concentration of solutions in Table 1 are not the same as the solubility in scientific literature; they are the values that have given me the best results. Depending on impurities and humidity, your ideal values might differ from mine. But it should be within 5%.
- I discovered another hydrate of magnesium sulfate that forms rhombic crystals. It grows from extremely concentrated solutions (> 100 g / 100 mL?). Preliminary tests suggest it is the hexahydrate.
Single crystals of magnesium sulfate (hexahydrate?). To my knowledge this is the only picture of them on the Internet. Growing them is beyond the scope of this guide – but if you’re an expert looking for a challenge, give it a try.
That’s all for this guide. I hope you enjoyed it. If you’re looking for more pretty crystals, check out my previous article on growing crystals from a common fertilizer, make cubes from table salt, or grow striking blue copper sulfate crystals.
If you’re looking for a cool hobby, or something fun to do with your kids, I highly recommend giving it a try. The crystals that you grow might dissolve in water, but the memories you make will last a lifetime.