Alum, found at the grocery store, can form beautiful diamond shaped crystals. The best part is, anyone can grow some within a few days at home!
It is also beginner friendly, easy to grow and completely non-toxic. You can have your first specimen in a week or two.
Of course, trying to grow extremely high quality crystals will take some skill and patience. But it can be done – and in this guide, I will walk you through the steps to do exactly that.
Before that, we need to get our alum. There are many types of alum. The one we want is potassium alum. It is normally used in pickling and also water purification, so you can probably find it under the baking section. Alternatively, you can also order them online. 250 g is more than enough for the first try.
This guide will be divided into 5 easy-to-follow parts as shown below:
- Preparing the growing solution
- Growing a seed crystal
- Growing a big alum crystal
- Drying and storing the crystal
- More cool activities with alum crystals
Preparing the growing solution
To grow our alum crystal, we first need to prepare the solution for it to grow out of. Think of it as something like salt water. When salt solution evaporates, salt crystals are left behind. Similarly, when alum solution evaporates, alum crystals are left behind.
- Dissolve 60 grams of alum powder in 500 ml of hot water. Stir the solution using a spoon until all of the alum dissolves.
- Filter the solution with a coffee filter to get rid of any dust. Tissue paper also works.
- Wait for the solution to cool to room temperature.
Growing a seed crystal
After cooling, sprinkle a few grains of alum powder into the solution. Tiny crystals should start forming in the solution within 30 minutes.
This is where my guide differs from others you can find online.
Do not be tempted to grow these small crystals. Leave the solution alone for 2 days. This step will ensure that you get more beautiful crystals in the end.
Some crude crystals that formed at the bottom of the container. It’s a good start, but they are not what we are after.
After 2 days, pour 50 ml of the alum solution into a flat dish, and the rest of the solution into a transparent jar/cup. You only want the solution – leave the crystals at the bottom of the original container behind.
Leave both the dish and the cup containing the solution in an undisturbed place. Beautiful crystals will start forming.
After a few days, your dish will contain many small, clear crystals. Once the crystals reach 0.5 cm in size, select the most beautiful crystal inside the dish.
Excited? I bet you are! Then, tie the crystal to a fishing line (or a string), taped to a stick.
Lower the seed crystal into the cup containing the remaining solution.
Place the cup in an undisturbed place, and all you need to do now is to wait!
Alternatively, if you don’t want to tie the crystal to a string (because it will get stuck inside), you can also grow your seed crystal at the bottom of the same cup/container. Here’s an example:
Growing a big alum crystal
As the solution evaporates, alum particles will be deposited on your seed crystal.
Therefore, it will slowly grow larger.
You can stop growing it when:
- You’re satisfied with its size
- The level of the solution has decreased so much that it’s about to expose the crystal
You never want the crystal to be exposed. Otherwise, its surface will no longer be smooth and clear.
A crystal that waited too long until the decreasing water level exposed it to the air. Note the rough and dull edges.
Regardless, when you want to stop growing, take it out, and dry it using a piece of tissue paper. Do not wash the crystal or you will cause it to re-dissolve.
And that’s it, you’re done!
Storing the crystal
If left in open air, your alum crystals might slowly turn white over time. This is because alum crystals have water molecules trapped inside their crystalline structure, and as that water dries up, the crystal turns white.
To prevent this, just coat the crystal in a layer of nail polish. This method works well, and the crystals that I’ve coated look the same even after a few months.
Alternatively, keep the crystal in an airtight container, together with some alum powder. The alum powder will sacrifice itself, and in turn, provide a stable atmosphere inside the container so that your main crystal does not dehydrate.
Alum crystals are not very hardy. It’s fine to handle them, but they do crack if you hit them too hard. This, and the fact that they dissolve in water, makes them unsuitable for jewelry. I suppose you could seal them in epoxy, but I haven’t tried that before.
More cool activities with alum crystals
Growing alum crystals is fun. You can take this one step further by growing them on objects.
If you want to grow a single big crystal, just follow the procedure above, but place the seed crystal on the object of your choice. Here’s a beautiful specimen by Reddit user u/Higurashii who kindly shared it with me:
Other than that, you can also coat an object with a layer of small crystals. To achieve this, immerse the object in a supersaturated alum solution. Unlike the steps for growing large single crystals, this technique will cause lots of small crystals to form at once. It’s not what we want in the procedure above, but perfect for crystallizing objects.
Many people like to grow crystals on insects, tree branches or sculptures using this technique. Here’s a beautiful crystallized crab by taxidermist Jamie Keiman. Check out more of her creations on her Instagram page.
Because alum crystals refract light, you can even use them as prisms. One morning, I saw a ray of sunlight coming through the window, and I tried putting one of my crystals in its path. The result was beautiful!
Here’s an unedited photo of the refracted light. Rainbows are cool!
And when I moved the crystal around so that the sunbeam hit it at different angles, specks of light danced around me.
That’s all for this guide. Hopefully you found it useful.
Growing crystals takes time, but with patience and a little bit of luck, you can definitely create sparkling gems at home.
If you have any questions, feel free to put them down below.