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.
Alternatively, check out my post on growing crystals with fertilizer. It’s even easier than alum, and produces spectacular results. Or take a look at how to grow crystals from table salt.
Happy growing!
Hey, Chase. Thanks for the instructions. I’ve attempted to make two solutions following these steps, one with potassium alum, and one with chrome alum. While I wait for my seed crystals to form, I have two questions.
1: At the start, how hot is “hot water”? I brought mine up to 160 F before dissolving 60g of alum powder into 500 ml of water. Was a full rolling boil necessary?
2: The chrome alum solution is, unsurprisingly, very dark. Not even a flashlight held directly against the glass will illuminate the solution. Do you have any suggestions for figuring out the state of crystal growth within it, or finding and fishing out a good seed crystal?
1. The hotter the water, the faster the alum crystals dissolve. I tend to use boiling water – but it’s actually not important at all. The main objective is to dissolve all the alum powder.
2. Grow seed crystals by pouring the solution into a shallow dish (~1cm deep), and place a piece of white paper underneath the dish. Better still, place the dish on a transparent surface like a glass table, then shine a flashlight underneath it. You’ll be able to see your seeds clearly.
P.S. If you’re planning to grow bigger chrome alum crystals, don’t use too much chrome alum in proportion to the regular alum. The final crystal will be practically black, which is not as nice as a purple crystal (at least in my opinion).
Thank you for the response! I ended up with *nothing* growing in the K alum petri dish or solution at 60g alum per 500 ml water after five days, and I hadn’t seen your reply, so recombined it, boiled it, and added nearly double the amount of K alum to the solution. It just kept dissolving! At something like 8 total tablespoons (easily over 130 g of K alum in the same 500 ml of water), I filtered it, let it cool and followed the rest of the procedure. After eight days, I had nothing in the main beaker and a thin sheet of frost-like crystals across the top of the petri dish (https://i.imgur.com/LbZj0Yl.jpg) which were slushy and soft when I tried to break them up to discard them. I’ve tossed a small bit into the main solution beaker, but they dissolved within hours. No crystals have formed in the main beaker.
I’m concerned at this point that either my K alum is the wrong kind (I bought the stuff you’ve linked at the top of this page), or there’s something in my tap water preventing normal growth, so I plan to order a different batch of K alum, get a jug of distilled water, and try again. Any thoughts on why I’m getting such odd outcomes? Do I just need to be more patient? 😀
(Chrome alum seeds worked, though! I was about to throw it out as a failure when I noticed a good one in the petri dish. https://i.imgur.com/MjKyeZG.png)
Hey there. I think the problem is that your solution was initially undersaturated. After pouring the solution from the beaker to the petri dish and letting the water evaporate, the solution slowly became supersaturated but no nucleation sites formed. Then, once a nucleation site formed, the solution was already VERY supersaturated, hence the frost-like crystals growing very quickly in a matter of minutes. Since they dissolved after putting it back in the beaker, it means that the solution in your beaker still needs more alum. So you might have to add more haha. It takes some experimenting to get to the sweet spot, and it varies based on location and alum purity, but once you have it nailed down you’ll never have to worry about it again.
To avoid the frosty crystals in the future, I suggest you sprinkle a few grains of alum powder into your solutions every now and then (when no visible crystals have formed yet). These alum grains will produce sites for crystals to grow.
Congrats on the chrome alum crystal, it looks beautiful!
Hi Chase, thanks for this! I am looking for a way to create black crystals, do you have any idea how I can achieve that?
Thanks!
You can take a look at growing copper acetate crystals from scrap copper and vinegar; they are naturally black. Otherwise, it’s hard to dye a crystal that isn’t naturally black (like alum), because crystals like to exclude dye from their structure when they form.
Hey, Chase! I love growing alum crystals! I am just now growing an alum crystal according to your (awesome!) instructions, but for some reason, the solution isn’t growing anything! 4 tablespoons of alum dissolved in 500mL of water. I sprinkled on powdered alum, (about 1/8 tsp.) and I can see them in the bottom of the glass. Is there something I’m doing wrong? I do have the glass in a windowsill, so maybe the sunlight is affecting the crystal growth.
Anyway, I’d be happy to hear your thoughts! Happy crystalizing!
Hey there. The solution probably isn’t saturated. Sometimes, an undersaturated solution can still have alum powder sitting at the bottom because the solution at the bottom is more concentrated than the solution at the top. Therefore, it can take a really long time for the crystal powder at the bottom to dissolve to saturate the solution. Only a properly saturated solution can form crystals. You can solve this problem by:
1. Add a little more alum to the solution.
2. Heat it with stirring until everything is dissolved.
3. Leave the now saturated solution to cool.
4. Filter it and pour it into another container.
5. Sprinkle a tiny bit of powder inside.
6. This solution should now form crystals.
Sunlight doesn’t have anything to do with it (unless the weather at that place is hot, which will speed up evaporation and thus, crystal growth). Good luck!
Thank you so much for your amazing, detailed response, Chase! I will do that right away! (Thanks again for your website! It’s AWESOME!)
Hi Chase, this and your MAP-based crystal instructions are both great, thank you for publishing them!
I have a small amount of potassium aluminium sulfate (Kroger brand alum) which I’ve been doing some experimenting in crystalizing, but I’d like to try it at a larger scale so I decided to buy in bulk from amazon. I initially bought what I now realize is just aluminum sulfate, so I got some potassium sulfate as well to synthesize it myself.
Based on what you said in another comment as well as a different website, I should use 1 part potassium sulfate to 4 parts aluminum sulfate, right? Do you know approximately how many parts water would produce a supersaturated solution?
Also, would a similar procedure as in the MAP guide work for these types of crystals, where you first use a supersaturated solution for seeds and then make a less concentrated growing solution for larger crystals? Or is it best to use longterm evaporation like in your steps here? My goal is to grow crystals on a branch like in your MAP guide, but I don’t want to invest into a different chemical just yet.
Sorry for all the questions and thanks again!
Hey David. The answer to your questions are available on this page:
https://en.crystalls.info/Aluminum-potassium_sulfate
Check whether your potassium and aluminum sulfates are hydrated or anhydrous, because that will affect the measurements. Suppose that you manage to prepare 100g of potassium alum from the two raw materials. Then treat the 100g of potassium alum you synthesized just like potassium alum you bought from the store (the solubility remains the same).
Hi,
im doing my PHD in Physics right now and my Thesis is all about growing crystals with a molecular beam epitaxy device.
I stumbled across your website and im just amazed of what beauty is achievable with kitchen utilities. Ill deep dive right away and will share my results if any of them are worthy.
Right now i have table salt, sugar and alum solutions sitting prepared in the darkness to eventually form crystals.
Thanks in advance! There is nothing comparable on the internet in terms of guides.
Hey there. That’s so cool! I’d love to see what you come up with.
Hey Chase! This is my first time trying crystal growing, and I wanted to say thank you for getting me so interested in this hobby! With this alum crystal being my first one, there were a few things I was wondering about.
December 28 at about 8:30 PM: Prepared the solution (in a glass cup) and sprinkled some alum into it after it cooled.
December 29 at about 7:30 PM: Nothing happened since I sprinkled in the alum. The grains I sprinkled in hadn’t even dissolved. I was a little confused, but after reviewing other comments I figured my solution was exactly saturated. I went ahead and moved on to growing a seed crystal (I don’t have a glass petri dish so I ended up using a small circular metal dish instead, still pouring only 50mL into it).
January 1 at about 8:30 PM: I check the dish and am ecstatic to see that 2 beautiful clear crystals are sitting at the bottom, each roughly half a centimeter wide! Small note – there don’t seem to be any other crystals in the dish here at all.
About an hour later, I have the best-looking seed crystal suspended in the solution and everything is set up properly! Another small note – I ended up using some fluorocarbon fishing line instead of nylon, since it’s what I had handy.
January 6 at 1:10 AM (Right Now): I still don’t think there have been any changes in size, so I was wondering: How long does it usually take for the crystal to grow? Are/were there any errors in my procedure? I have patience but I figured I should ask, especially since my solution behaved differently than it should’ve at the beginning. I’m also growing my crystal on my kitchen counter, and it’s usually a bit chilly in that area (especially since it’s winter).
Here are some pictures if it helps!
https://imgur.com/VFNljLn
I also left the other seed crystal in the metal dish just because I was curious to see the result, and lots of small crystals formed at the bottom by January 4!
https://imgur.com/QauebU5
This is what my seed crystal looks like right now (1:14 AM on January 6).
https://imgur.com/yOyga0l
Thanks so much for your time and for replying so actively to your comments! 🙂
They’re beautiful! It looks like you got the procedure exactly right. Thanks for taking the time to share; I bet a lot of people will find your experience useful.
It’s completely normal for hanging seed crystals to take a long time to start growing. Like you said, your solution is exactly saturated, which means no crystal growth (or dissolution) will occur. It might take up to a week before the crystal starts to noticeably grow. Once it gets started, it should get bigger reasonably quickly.
Oh, that makes so much more sense! Thanks for clearing that up for me – I’ll definitely keep you updated!!
Hey Chase, sorry for taking so long to update you. My crystal did end up growing after about a month or so and I believe it turned out okay! This was very fun to do, and I definitely plan on following more of your guides for other types of crystals! 🙂
https://imgur.com/a/U7slm1c
https://imgur.com/a/MJXjPaC
It’s okay, crystals take time to grow. I must say, yours turned out great! Try putting them under a ray of morning light and see whether specks of rainbow light come out.
Good luck for your future crystals 🙂
Hi Chase,
I have tried twice now to grow this and I think I must have got some impure alum. What I bought is the 250g of this ebay listing: https://www.ebay.com.au/itm/254075134630
The first attempt I made I didn’t have a scale to weigh 60g, I just kept adding to the solution if it kept dissolving guesstimating about a quarter of the package. I ended up adding more than that, so much that I eventually stopped, without ever getting to a point where I thought the solution was saturated.
The week after I got a scale, and weighed the 60g addition. The following day still nothing had grown so I added the rest of the mixture (75g) and still nothing has grown… in either solution! So in total I used all 250g of what I bought across two solutions, and after a week I still don’t have any crystal growing at all.
Is this because I bought the wrong alum?
Ah. I think you bought the wrong alum. The product is misleading: the title says potassium aluminium sulfate (which is correct), but the picture says aluminium sulfate (which is not correct). I think they mixed it up and gave you the aluminium sulfate.
If you’re unsure, just buy some alum (potassium aluminium sulfate) that looks like chunky rocks. That will be the right stuff.
Thank you for the response!
After I choose the nice seed crystal, and poured out solution into the clear plastic cup to grow, the next day I had a bunch of small seed cystals forming along with the main seed crystal, is it because of dust getting in or should I filter it twice with coffee filter?
Should I cover it with a cover filter to prevent dust particles from forming seed crystals?
Also the alum I used was already in rock form from the grocery store, not powder, I hammered it and dissolved it. I did not need to use the small dish to grow the seed crystals because the crystals in the main jair that cooled off already looked like the very nice seed crystals in your dish. I don’t know why this is but made the seed crystal step easy, but its also too easy to form seed crystals instead of growing one big crystal like in your last step
The main reason many smaller crystals formed alongside your main seed crystal is because your solution is still too saturated. This is one of the reasons why you should let it sit for a few days to allow the supersaturation to decrease. A less supersaturated solution will cause less crystals to form, but allow the few crystals that do form to grow well.
This is epic! Thanks Chase
Hi, I don’t have coffee filters but I’d like to clarify what you mean by tissue paper. In my mind Kleenex or paper towel would fall apart if I poured water through it. I haven’t started anything yet. Just wondering about that first. 🙂
Near site & enjoy your Imgur posts
I’ve tried paper towels before and they work just fine. If you’re worried, try pouring plain tap water through a paper towel and see whether it holds up fine. If that works, it will also work with room temperature alum solution. Otherwise, you’ll have to get a coffee filter.
Hello Chase, and congratulations for your wonder site!
I love crystals and I decided to start trying with alum. However, I’m having trouble with the filtering. I tried both a coffee filter and kitchen tissue, but the liquid seems to be filtering extremely slowlyand leaving a lot of residue behind (it seems like most of the alum is being kept in the filter). Am I doing something wrong? No matter how much I stir the alum and the hot water, a lot of residue forms on the bottom after a while and I get the impression this ends up quickly blocking the filtering paper.
Hello! How much alum did you dissolve in the water? Is the solution initially clear, or was it cloudy from the beginning? Does the residue look like it’s muddy, or is it crystalline?
If it is crystalline, it’s likely that you dissolved too much alum and supersaturated the solution, so try using less alum next time. If it’s muddy, it’s because your alum was impure, so there’s nothing much you can do about it. Just let it filter slowly, and use the clear, filtered solution to grow crystals.
When I tried to dissolve the alum powder in the hot water, the resulting liquid was very cloudy, basically it was like milk, completely white. Should it become transparent? Do maybe my alum isn’t adequate? Or maybe I had to stir it for longer? Maybe the water wasn’t hot enough? For how long do you need to stir the alum?
Oh, by the way, I forgot to say I used the quantity of alum and water you provide in the guide.
In that case, I think that the alum you used is impure. No matter. Just dissolve as much alum as you can, and leave the unfiltered solution standing for several days (a week if necessary). All the sediment should settle to the bottom. Then carefully decant the clear solution into another container, leaving the muddy stuff behind. You can then start growing the crystals.
Thank you! I’ll try that 🙂
Hi Chase,
I’m currently trying to grow my own crystals at home at the moment on to a silk knitted sample I made. I followed your directions but still nothing seems to be growing. I live in London and not sure if the hard water is potentially affecting this. please let me know if you have any advice on what to do!
Silk is pretty smooth, you might have some trouble to get the crystals sticking to it. Try preparing a more supersaturated solution by dissolving more alum in the same amount of hot water. Then, coat the knitted sample with some alum powder before dipping it into the already cooled solution. This should make it more likely for crystals to attach on the sample.
Hi, Im trying to grow some alum crystals, ive got the alum dissolving in hot water, but whenever it cools, lots of white powder forms at the bottom of the container, and if I filter the white powder out, any alum I put in the solution dissolves and forms white powder within 2 hours or so of dissolving.
I attempted to reheat the solution and adding 5g/ 100 ml of alum, and after stirring, the alum was clearly fully dissolved, but when it cooled enough for me to try to sprinkle some alum in (for seed crystals), there was a layer of white powder on the bottom. Any extra alum I added dissolves and later forms white powder about 1-2 hours after dissolving. Ive used an entire 250g bag of potassium alum powder attempting to get this to work and I am stumped.
Any pointers as to what I could be doing wrong?
Is there a huge amount of white powder? Or is it just a thin later?
Don’t pour your solution away. Filter your remaining alum solution into a new container. Then it should not have any white powder. After that, heat the solution to evaporate off more water, until small crystal flakes start to form. Wait for it to cool. You’ve just made a saturated alum solution without white powder, that you can use to grow crystals with.
In short, since you’re having a problem with *adding more alum*, just prepare a solution and *remove excess water*. Both procedures achieve the same result: producing a saturated solution that is suitable for crystal growing.
Hey there Chase, thank you for the guides! You’ve inspired me to try crystal growing. I’ve tried to create the solution for the Alum, but struggled to see any crystal growth after half an hour or even a day or two.
After reading comments, my alum grains don’t seem to grow and just seem to be sitting on the bottom, maybe my solution may not be saturated enough, or it’s just balanced in its saturation (even after reheating it and adding more Alum once, as you suggest). Out of curiosity, I have a couple of questions:
1) Are there a certain number of times the solution can be reheated before it becomes ineffective? Or can it be reheated, cooled, etc. indefinitely until you notice the crystal growth?
2) If, for example, I started with a new solution, how accurate must the measurements be? Is it better to put more than you think, potentially creating an over saturated solution to ensure potential crystal growth, or is that not recommended?
Thanks in advance for any reply!
1) The solution can be used indefinitely. If you use tap water, repeated dissolving/evaporation cycles might cause the concentration of impurities to build up in the solution, and slightly affect subsequent crystal growth. But unless you’re using it many, many times, I wouldn’t worry about it. Furthermore, crystals will always form, it’s just that their shape might be different due to the impurities.
2) If like me, you’re doing it at home, it’s not possible to get an exact measurement to guarantee saturation. The difference between 0.1 g of alum can mean that either the crystal will grow quickly or slowly dissolve. Temperature will also affect this value. Therefore, I always make a supersaturated solution to ensure crystal growth, and let it slowly bring down the supersaturation. It is highly recommended!
Note: If you’re frustrated that crystals are still not forming after many tries, do test run with a massive amount of alum. Try to dissolve 25 g alum per 100 mL pf hot water. This will guarantee precipitation of alum crystals as they cool, and reassure you that the alum isn’t magically disappearing into the water. Then you can bring down the supersaturation from there.
Hi, Chase!
I’m preparing to make my first crystals and I have questions about the utensils I should use. Do you use plastic or glass? Are both fine?
Also, I’m confused in some steps. When we put our solution apart while we wait for the smaller crystals to form and while we are growing our final crystal, do we have to cover the solution in some way to avoid evaporation?
Thank you!
Both plastic and glass are fine. If you’re planning to hold hot water in them (when dissolving the alum), then make sure you use heat resistant material.
Yes, cover the solution when you put it apart. There are 3 reasons for this:
a) To prevent evaporation
b) To keep out dust
c) To discourage crystals from forming inside this solution
Good luck!
Could I smash a solid Alum to powder?
Sure you can.
Hey chase I’m at the step where you sprinkle some alum into the solution after it’s cooled and have left it for 1 and a half days and have seen no crystals forming at all is it because I have the bar closed or is there something I’ve done wrong?
How about the alum that you sprinkled into the solution?
1) If it is still there, and unchanged, your solution is exactly saturated. You can proceed to the next step, which is pouring the solution into a dish and waiting for seed crystals to form.
2) If it has disappeared, your solution is undersaturated. Reheat the solution and add about 5 g more alum per 100 mL water. Repeat the procedure.
Can I put the solution in the fridge for it to cool down quicker or is it better to wait?
You can do both. Quick cooling vs slow cooling doesn’t matter when preparing the solution. But temperature changes are very important when actually *growing* the crystal, because a sudden change in temperature might cause the crystal to dissolve or develop cracks.
Also (sincerely sorry for nagging again) after The solution has cooled down when I sprinkle the alum in do I close the jar afterwards or leave it open?
Haha it’s okay. Close the jar to keep out dust.
Hi Chase, awesome article, can’t wait to get started making crystals. I bought some alum but just realised it’s aluminium sulphate (can’t see any reference to potassium on the pack). Will this still work?
Hey Jesse. Just aluminum sulfate won’t work; you’ll need potassium aluminum sulfate.
P.S. If it’s cheaper, you can also buy potassium sulfate, and mix aluminum sulfate with potassium sulfate in a 4:1 mass ratio. The product is potassium aluminum sulfate, which is exactly what you need to grow crystals with.
Thanks! My seed crystals are almost ready. I’d like to add some red colouring at the next stage. Would you suggest preparing a saturated solution with the colour before adding it to the filled containers (e.g., 6g alum powder in 50ml food colouring, as per recipe)?
Yes, you can do that. It’s alright to add food coloring anytime during the growing process.
Whenever you’re doing something new (like adding food coloring), add it to a a solution and *test* to make sure that the solution is indeed saturated. Sometimes the addition of something else will change the saturation slightly. You can do this by dropping a few grains of alum inside to check whether they dissolve. If they don’t dissolve (and don’t become huge and ugly all of a sudden), then you know it’s safe to add your seed crystals.
All the best!
Can you use a spray can of clear acrylic on them to seal? It seems like nail polish would take a long time on a large piece and leave brush marks.
Yup, sure you can.
Hi Chase, I love this article, lots of good information here.
Do you know if your method would work with
Aluminium Potassium Sulfate Dodecahydrate? This is the only thing available to me at the moment.
If so, how much of it will I have to mix in 500 ml of water?
Thank you!
Thanks! Actually, the alum I was referring to is exactly aluminum potassium sulfate dodecahydrate. So, just use the amount specified in the guide and you’re good to go!
P.S. There are actually other types of alum like ammonium alum and chromium alum, all of which have similar growth characteristics but different solubility. Potassium alum is the most common one.
Thank you Chase. Growing crystals is turning out to be a lot of fun.
Just a few more beginner questions if you don’t mind!
– I’m making different crystals using copper sulfate, alum powder, MAP and borax. Will they melt in summer?
– Do I need to regularly coat them in clear nail polish, or is once enough?
– Is there a way to grow crystals using Iron (II) sulfate powder?
Thank you very much!
Sure!
-No, the crystals will not melt. They will only dissolve in water. However, higher temperatures might cause drier air, which will cause the crystals (except MAP) to dehydrate and become white. This can be prevented with a coat of nail polish.
-Just one or two coatings of nail polish is enough. You don’t have to keep coating them.
-Yes, just dissolve the iron sulfate powder in water, add a little dilute sulfuric acid (to prevent iron hydroxide from forming), and use the same procedure that I showed in one of my articles.
I’m interested in growing some crystals that will be safe to cast in epoxy. Also, some that could be colored with food dyer or something? GREAT site though, I just stumbled on it this morning!
Yes, you can cast the crystals in epoxy. To color the crystals, just add a large amount of food coloring to the solution. However, the coloring will just give a light tint, because crystallization is a process that naturally excludes impurities (and dye). If you want colored crystals, I suggest you just grow crystals out of a compound that has the desired color. For example, chrome alum crystals are naturally purple and have the exact same shape as normal alum crystals.
Hey Chase:
We tried this at home (using someone else’s instructions) for my son’s science experiment. We did not have any crystals the next morning, it just looked like I dissolved alum at the bottom of the jar. I did notice there were some spec of dirt in the bottom of the jar my son chose and we tried to remove them but couldn’t get them to easily come out b/c they were so small. Could that have caused the crystals not to form? I’m going to try your method and see if it works. My son needs them by Monday. Today is Thursday! Thanks for a great tutorial!
Hey there. I don’t think the dirt is the problem. Maybe you guys didn’t dissolve enough alum into the solution, hence the solution is not saturated? A solution that is not saturated will not form crystals.
Try sprinkling some alum powder into your solution. If the grains of powder start growing, great, the solution is saturated, and you can proceed with growing them. If the powder disappears (dissolves), it means your solution is undersaturated. To fix this, just reheat the solution and add about 10% more alum. After that, you can do the test again. Good luck!
I use potassium alum crystal as a deodorant. Can I smash the leftovers to a powder and use that? It feels like such a waste to just throw them away…
Yup. It’s a perfect source of alum. Then you can tell people you grew shiny crystals from deodorant haha
How would you make these crystals coloured?
The easiest way is to add food coloring. It won’t completely color the crystals, but there will be a light tint of color to them. Alternatively, you can grow chrome alum crystals (potassium chromium sulfate). They have the exact same structure and can be grown using the same procedure, but they’re dark purple instead. Since this purple color is natural and inherent to the crystal, it will turn out much better.
Hi Chase. Very nice article, crystal and photos, congratulations. I have a question, sometimes in the alum solution, mold or bacteria appear that at some point eat the crystal and it stops growing and loses its luster. is there a solution to this?
The easiest way is to prepare 2 solutions. Use one solution to grow the crystal. Once you see the slightest signs of mold forming, move the crystal from the 1st solution to the 2nd solution. Then, boil the 1st solution briefly to kill the mold. When the 2nd solution starts to mold, you can swap them again.
You can also try dropping a piece of copper metal into the solution, as copper is toxic to microorganisms. Some people have successfully dealt with this by adding small amounts of iodine to their solution.
Thank you very much for the interesting information. all three sound good. I will try iodine first, it looks easy but I’m afraid the color in the solution will not change. I have had an alum crystal for 14 years as a student. it is as beautiful as then. I like to use an amorphous quartz base and have the crystal grow on it. this makes it look like by nature. unfortunately since I saw mold in my solutions I was disappointed and did not bother again. I hope to see good results with your 3 tips. thanks again Chase. !
I have a student who would like to cite your web article in a bibliography. Can you please send me the information so we can do this properly?
Sure. I’ll email you the details.
Hi Chase, do you have any suggestions for suppliers to get bulk material? I want to do a lab in a university class. The best I’ve found is 10 – 30 lbs of food grade on ebay. Thanks
Hey Joe. I’ve never bought alum in bulk before, so I don’t know of any bulk suppliers. 30 lbs is a decent amount – you can prepare 100 L of saturated solution with it. For crystal growing purposes, good for 150 individual students.
made a solution with 100 g of alum potash salt and 400 ml of water and it has been 2 months but it is only 8mm X 6mm .Can you suggest how can i grow it faster and to size of 1.5 cm X 1 cm
How much time will it take
It really depends on the conditions where you live and the size of your container. I recommend doing 2 things to speed it up:
a) Make sure there are no small crystals growing at the bottom of your container
b) Move the setup to a place which is more exposed, like on a bookshelf (but not outdoors).
There’s also a method where you prepare new supersaturated solution and add it into the growing cup, but there’s a big risk it will make the crystal opaque and ugly, so I don’t recommend it.
Expect to wait another month to reach 1.5 cm^3.
I want to display my crystals. Could I give it a coat of clear nail polish? Or would that start dissolving it?
Nail polish is a common way of preserving crystals. It should be fine.
It almost looks like you added Borax to prevent the octahedral structure from taking over the cubic structure completely. Did you add anything to get that effect or did it just occur naturally?
Good observation! Unfortunately, no I did not. Maybe it was because I was using food grade alum, and impurities inside it affected the growth of the crystals in a similar way to borax.
Can you coat the crystal in a clear
nail polish to preserve it?
Absolutely. That is indeed a good way of preserving the crystals.