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How to grow sodium chloride crystals at home (crystalverse.com)
1119 points by kdavis on Nov 17, 2021 | hide | past | favorite | 180 comments

My daughter has this as an school assignment, with some implication that it is some sort of a contest, and we managed to grow quite a few of similar quality to the seed crystals on the site in 4 days, which was the original (poorly thought IMO) deadline. The trouble is that no one else was able or cared to do it so fast, so the deadline has been slipping for a couple weeks now, with our best crystals going to school and back a few times, getting scratches and broken bits instead of nicely growing undisturbed. A bit discouraging. I'm now remembering how frustrating was for me to take school related things too seriously and discover you cared more than your teachers when I was her age.

We managed? When I was a kid I never got help from my parents on these projects, and hated the kids who "won" because their parent helped.

On the other hand, being the competitive person who excels in science projects is often a very good predictor for being able to handle the tedium of a scientific lab job.

> When I was a kid I never got help from my parents on these projects, and hated the kids who "won" because their parent helped.

These can be two different things:

1. Constructive help from parents has (at least) two components. First, it shows your child you care. This may seems small, but it’s not. Second, and I think this is what a lot of HNers would appreciate, is to help your child to develop good processes. There is a lot that goes into this, and it can be parent-centered or child-centered, but having your child reflect on process and (ideally) implement some good processes can really set them up for later in life. Imho, parents should have to write a short narrative about what involvement they had in their child’s project, if any. This is required at some of the local schools where I live.

2. Having the parents do the project for the child is just silly. Most decent teachers can see through this (assuming they care). Congrats to the adult parent for winning elementary school or middle school as an adult. :-/

> Most decent teachers can see through this (assuming they care).

I entered the science fair as a kindergartner with a poster project explaining how (the output color-mixing of a) color TV worked.

Principal accused my parents of doing it; they had no idea what he was talking about and protested that I’d done it. So he interviewed me about it and left convinced I’d done it. ;)


When in doubt, a simple question like “why did you choose this topic?” or “what was the hardest part of this project?” will usually make clear the driving force behind the project. Some younger kids will just blatantly admit that their parents did the project (sometimes/often to the child’s dismay).

I flunked kindergarten. (That year the school tried an experiment, and kept half the class back in something called Early Primary. I think the experiment failed. I was the shy nervous kid hiding in the playhouse though.)

I had an english teacher in college accuse me of cheating. Well accused me in a roundabout way. My paper was on psychosurgery, and violent criminals. He said he needed to ask his girfriend, who had MFCC, how to pronounce amygdala. From then on I dumbed down my papers for him. I would purposely use a bunch of semicolons, and dashes.

I loved to write until I had that guy as a teacher.

Yep. I got some help from parents, but it was basically stuff like using things that might be too dangerous for a little kid (power tools), or under close supervision, and asking questions about my plan.

I think the big part is to be a mentor. Just asking questions like 'did you think about x', or 'how do you plan to handle y' can have a huge impact by making them think further into the plan without just handing them answers. In my opinion, having them think about the possible outcomes and then search out additional information is really what school is supposed to be about.

My memory of my kid’s school years include a lot of disrespect by the school, PTA, and other parents of my family’s lives, boundaries, and resources.

My memory of being a kid is that I could not count on my parents to do something I needed. I probably could not have gotten that short narrative from my parents and all it would say if either actually did it was “I didn’t help.”

So, on the one hand, as an honest parent I find such a requirement boundary crossing and a(nother) waste of my time; time I could spend doing something meaningful with my kid. On the other hand, as a former kid, I find the requirement a dealbreaker and I wouldn’t have even tried. Meanwhile, dishonest people are just going to write dishonest narratives.

Do you have some examples of that disrespect from "other parents"?

Sure, a couple stand out. First, we were to volunteer a certain number of hours to a parent-run fundraising organization. I forget the actual process of how this requirement worked; except that among the pile of paperwork parents are given to sign was an agreement to do the work. We didn't mind, so we signed and included a list of our skills.

In practice, what happened was that after we had done our hours, they asked us to do more hours. We said no. Then they cajoled us. We said no. They then essentially harassed us and implied we didn't care about our child if we didn't do more hours. We said no, but this still went on for awhile. You can't escape them either. Even after they stop calling, they gossip about you and get passive aggressive at events. I talked to some parents of older kids and was told that the volunteer organizers only ever bother the parents who actually volunteer. They don't bother with the ones who never do their hours because they figure they never will. So these parents just stopped volunteering altogether. After a couple years of this, I followed their lead.


The school my child attended was in the same physical building and had the same administration as another school. The two schools used different teaching methods. The population of the school my child attended was about 30% of the population of the larger school. Both schools were neighborhood schools. If you lived in the neighborhood and applied, you got into my kid's school. If you didn't apply, you got into the larger school. If you lived outside the neighborhood you could apply for either school, and IIRC, you got in through a lottery process and only if there was room. In practice, no one ever applied for the larger of the neighborhood schools, only my kid's school. Most people just didn't apply, so my kid's school was smaller and about 30% of those kids were from outside the neighborhood.

Each school had its own PTA. At one point, the larger school's PTA approached our PTA about merging into a single organization. It made a lot of sense on paper, especially since there were "all schools" events. So it happened. The president of the larger school's PTA stayed president. Her first act was to send out a letter to all the parents talking about the merger. It also talked about "putting an end to the special treatment of a select few." In other words, our kids weren't going to get their school-specific field trips that were made possible by our volunteer hours and other fundraisers.

The subsequent meeting was eye-opening. They talked as if the kids' of the smaller school were all little Gates, Zuckerbergs, and Musks, even though most of us lived in the same neighborhood and I only knew of one family with any significant money. Most of these people were wealthier than me just by virtue of owning property in the Bay. We lived in an apartment with rent we could barely afford that was larger than a lot of these people's mortgage payments.

What we thought was going to happen is we were going to merge our PTA's hard-fought opportunities with their sheer number of parents to raise more funds for everyone. What they thought was that we had more money because we were rich and it wasn't fair and they were going to take it and give it to their kids.

The mandatory-voluntary PTA work reminds me of a college course I had (sociology). The professor was also a Scout mother and told us we'd be doing X hours of "volunteer" work for her son's troop but it would be part of our grade for the course.

As the first in my family to go to college, I was working multiple minimum-wage ($5.85/hr) part-time jobs on top of a full course load just to afford to eat and live. I wrote the professor a letter explaining that this "volunteer" work would be an undue hardship because literally every waking hour that I wasn't in school I was working, so these "volunteer" hours could only come at the expense of work hours and loss of income (which was already not making ends meet).

Her response was that she didn't believe I couldn't spare X hours/week and wouldn't "bend the rules" for me - everyone had to volunteer. The exchange grew increasingly tense until I asked her how much was the activity worth? One letter grade. "Guess I'll be down a letter grade then." (It was a small university and required core course, so I couldn't just drop the class or take with a different professor.)

It's perspicuously clear to me that the professor was perpetrating serious academic and professional misconduct. It was entirely unethical.

Thank you for sharing. This sounds like a nightmare.

Bay Area schooling is yet another thing that makes Bay Area living less tolerable.

I interpreted it as "if the parents help with homework they have to write how much". I would hope that since your parents did not helped, no narrative is needed.

This is correct.

I have seen this most with larger projects, and usually the student was encouraged to seek outside expertise (just like one would do in real life).

The only catch was that the assistance from the outside sources needed to be documented.

For teens, they can do the documentation themselves. For younger children, a short note from a parent is adequate. If this is a burden to the parent, then I think there are probably some other issues involved.

The reality is that behavior 1 makes expectations on school projects just go higher and higher. As you said, parent making it completely is recognized by teacher. But what you call constructive help from parents is making actual difference in result while being much harder to recognize.

What you call constructive help is literally parent organizing and guiding whole thing. If that is what homework project becomes, then it should not be homework at all. It should be in-class experiment, because it so far from being autonomous kids activity.

> Imho, parents should have to write a short narrative about what involvement they had in their child’s project, if any. This is required at some of the local schools where I live.

Personally, I think that homework should be within kids abilities scope - including attention span, access to materials and ability to organize.

> This is required at some of the local schools where I live.

Like heck I'm gonna sit there writing short narratives for some school. Homework stops at the kids.

I’m guessing if they don’t receive a narrative from you they infer that you probably didn’t write the actual assignment.

When I was a kid I never got help from my parents either and I now think that I would have benefited from a bit of closer attention. I developed a huge spectrum of bad practices and behaviours that I'm inclined to think I could have avoided at least in part. I want to think there's some space between doing their homework for them and not caring about the minutiae of their education, and I want to be there.

A good framework I’ve heard for this is “scaffolding” - as a parent you can provide a little structure to help your child solve problems that might otherwise be out of reach. As the child learns you gradually step down support until they’re able to succeed on their own.

In the working world we call this mentorship. It’s surprising to me that the practice is controversial when applied to children that have so much more to learn.

Me too, I consider my parents good in most respects but the extent of their help was “if you get any Cs on your report card we will take away video games”. I feel like this was pretty normal for average middle class boomer parents and didn’t really know others were different until very late. My guess is the more coastal elite, immigrant or younger your parents are the more they see education as competitive and help.

> I want to think there's some space between doing their homework for them and not caring about the minutiae of their education, and I want to be there.

Even showing a lack of interest in their pointless projects is a life lesson in priorities and individualism.

But the project isn't pointless!

For example, most of my help was to make sure she took 10 different containers and placed them in different locations around the house to increase the probability of getting a few decent crystals. I discussed redundance with her in the context of explaining why some of her friends were not getting results from their single try. I think that these practical thought patterns are extremely valuable, better than creating a miniature jaded adult...

You're doing good. Just cause someone else's childhood sucked and they feel like they learned something from it doesn't mean it's a good thing. You learn a lot more about how to live well from being loved than you learn from being ignored and neglected.

Well said.

You sound like a great parent doing right by your daughter. She's lucky to have you.

The point of school is to learn to think + learn to face adversity & failure....

I mean, I sometimes help my kids in very similar way. But, I find it very wrong to judge kids who were truly independent or make such projects into competition between the kids. Because the real competition is here in fact in between adults. Parent knowing that "different locations around the house to increase the probability of getting a few decent crystals" is what makes the difference. Parent who makes sure the kid takes 10 containers is what makes difference. As you said, it is not within average kid going by school education to figure it out.

> The trouble is that no one else was able or cared to do it so fast, so the deadline has been slipping for a couple weeks now, with our best crystals going to school and back a few times, getting scratches and broken bits instead of nicely growing undisturbed. A bit discouraging.

The thing is, the "no one cared" is very unlikely. Those other kids did cared. But they were doing the project as kids do - loosing attention or doing it ineffectively. Forgetting and trying re-over. Having it at bad place and thus having it grow slowly etc. And all that is part of actual doing-projects learning. It is not bad pedagogy to have kids deal with these issues and have them slowly to figure it out. It is bad to then expect the similar result as your daughters had, when the most important decision making was done by you. Or judge those kids as "dont cared".

And this is an actual issue - a kid doing the project the way that is age appropriate and in fact independent ends up labeled as not caring kid. And I think there is value in kids figuring stuff out truly independently.

That's a really good point about the competition. When I was a kid, my siblings and I participated in an annual pinewood derby. It was fun to decorate our cars but we never came close to winning the races. The winners were the kids with parents who knew how to add just enough weight to keep it under the maximum and grease the axles and who knows what other optimizations.

> Even showing a lack of interest in their pointless projects is a life lesson in priorities and individualism.

If you teach your kid the lesson that life sucks and trying is for suckers, don't be surprised when they believe it and don't get anywhere in life because they never try.

Life doesn't suck and trying isn't for suckers but school isn't life. Trying more than the minimum necessary to get what you want out of school is just waste. If you find some cool subject or project at school that you genuinely care about then by all means go all out. But doing great work when excellent will get you an A and all you care about is a grade is a waste of time and energy.

yes indeed!

If you want to be a cynic don't have freaking kids.

I was enamored with "Things of Science" when I was a kid. So much so I began collecting them off eBay, scanning the little science booklet and sharing them for posterity.

As such I love DIY science like this.

Regarding crystals, I have scanned in and cleaned up two projects relating to crystals:



@JKCalhoun just got this account to say thank you for this - I am home schooling with my kids this year and this is a gem of a find.

You should be able to find many of the "things" in many of these kits. They were very well written, researched. Each "experiment" is a simple step along the way to understanding a concept (such as crystals).

Also from me thanks a lot for all your scans! They are wonderfully written and the experiments are a lot of fun!

Thank you for sharing Things of Science!

Wow, another thank you for scanning and uploading these, looking forward to trying some out with my kids!

I bet there would be a strong demand for a modern "Things of Science" - youtube is great and all but having a kit put together is a boon for parents

My daughter's only 2 and a bit right now, but I can totally envision an environment wherein I'm acting as an idiot sub-lab assistant role, helping with the basics of her demands.

Of course, I'd not want to do her work for her, but more than equally, I'd be quite happy to have a '5% We-encouraging' in her vocabulary when it comes to her explaining herself. What parent wouldn't, if they can?

“When I was a kid I never got help from my parents on these projects, and hated the kids who "won" because their parent helped.”

I wish my parents had shown interest in stuff like this and supported me to some degree. It’s not about doing the whole project for the kids but showing interest is super helpful. I often gave up on stuff because my dad would basically say “what’s this nonsense for?”

I noticed this when read books about Steve Wozniak and Richard Feynman. Their dads showed interest and encouraged them to explore the world and also challenged them from time to time.

As the person who said that I should point out that my parents did teach me and work with me on things, just not technical maker projects (pinewood derby, build a bridge and see how much it can carry, etc). Other kids had dads with garages full of woodworking equipment and had trained them. On the other hand, my parents provided me with a computer and the freedom to learn from it (the thing I liked about computers is that you didn't have to depend on other people as much to learn how they worked).

As an example of what I missed out on, while I was on a team of makers I was using a cordless drill and stripped a screw. A coworker poitned out there's a knob that controls the tension of a ratchet, so you can make t he drill stop spinning before stripping the screw. I had no idea, at 45, that was even possible. They had all known about it from early childhood.

I had the exact same experience at 35 - I was a self taught at home handyman and thought that it was inevitable that screws just get stripped! Funnily enough my dad was pretty handy at building, but the extent of my help was holding and gophering so I never actually learned much, except that it's possible to DIY.

I recall something about Feynman's sister not being encouraged. I don't recall if it was his father or his mother.

Sadly being a good parent to one child doesn’t necessarily mean being a good parent to all children.

> When I was a kid I never got help from my parents on these projects, and hated the kids who "won" because their parent helped.

It took me many years later to understand that those kids were actually getting help from their parents and I was not that bad actually

The sitcom Modern Family had an episode in which kids had to do an egg-drop project and were helped by their respective parents.


>I'm now remembering how frustrating was for me to take school related things too seriously and discover you cared more than your teachers when I was her age.

Perhaps it's you taking this children's assignment too seriously. Was the goal really to find who could grow the best sodium crystal, or was it to teach them how to manage a small project and learn a bit of chemistry? Did your daughter learn anything about those things?

That teacher has a bunch of other kids to educate. Maybe they don't care, or maybe you just have your priorities screwed up a bit.

I know exactly how you feel. Very frustrating and sometimes disenchanting to discover they don’t really care.

But perhaps also a good life lesson because that happens all the time. It’s good to try and develop a healthy self-driven passion. Oh, you don’t care? That’s fine because I do and I learned a lot.

This is a perfect experiment to do in class, letting them sit in the classroom to be revisited at the beginning or end of classes (maybe weekly?).

It doesn't sound as suitable for a take home project

I can't believe parents send their kids to public schools instead of home schooling. The only benefit is childcare and socialization. And those aren't necessarily always benefits either. I mean the amount of time wasted in school is outrageous. And I don't mean wasted as in the hyper ambitious tiger mom way, I mean situations in which you are sitting in a room doing nothing or on your phone or you are taking a test to prove that you know some information.

We just accept this as normal. Nothing is less normal than a bunch of children growing up in a building sitting in chairs all day. In an environment that is strictly controlling with harsh limitations on freedom of speech, no tolerance policies for all sorts of relatively innocuous things, and a forced secularism as to ingrain in students the unimportance of spirituality, physical health, personal liberty, and nature. And lets rid ourselves of this notion this is about education, because it isn't. Every step of school is focused on obedience and preparing them for the next step so they will be able to get a job. It is the perfect way to mold a child into an obedient wage slave.

>>A bit discouraging. I'm now remembering how frustrating was

I am picturing you over a mortar and pestle crushing the salt of your enemies whilst a single tear falls into the mix - and en-vigorating (filling with life) - the salt of your defeated enemies..

Could be a good self-sufficiency project too.

When I was an organic chemist, growing crystals was of paramount importance for certain structure determinations using X-ray crystallography (to answer "did I really prepare what I think I prepared?")

With sensitive compounds, sometimes you can't just let things evaporate. Also as the article states, weather conditions might mess you up. IMO the coolest trick we had to solve this was osmosis of an anti-solvent into a saturated solution.

A small sealed container with a saturated solution of your compound/salt is punctured, and put in a bigger sealed container containing a worse but miscible solvent for the compound under study. Slow diffusion into the inner container causes very reproducible crystal growth, as long as you can control the temperature.

> growing crystals was of paramount importance for certain structure determinations using X-ray crystallography (to answer "did I really prepare what I think I prepared?")

Ahh, X-ray crystallography, a.k.a. the field of modern (bio)chemistry that most closely resembles medieval alchemy.

The excellent 2009 documentary "Naturally Obsessed" [0] is about how difficult, time-consuming, and frankly irrational it can be to successfully crystallize certain proteins and protein complexes. The film is about how some PhD students spend the entire five-ish years of their degree programs trying (and mostly failing) to find the secret recipes (protein purity/additive ingredients/temperature/humidity/phase of the moon) that will allow their proteins to crystallize, and thus granting them data with which to populate their dissertations.

Why irrational? In one case, the secret ingredient is pickle juice.

[0]: https://www.thirteen.org/naturally-obsessed/

> Ahh, X-ray crystallography, a.k.a. the field of modern (bio)chemistry that most closely resembles medieval alchemy.

This is amusingly accurate and makes me wonder if our understanding and techniques will ever advance to the point where crystallography no longer feels like medieval alchemy. Surely the process is largely deterministic and we simply can’t control the relevant initial conditions with our current methods.

Fortunately cryo-EM is helping to overcome the cristallography bottleneck. B progress regarding cryo-EM resolution have been made in the last years.

Has it's own share of alchemy. Remember, the water has to remain vitreous. This is sometimes quite incompatible with the environment proteins want to exist in in their natural state.

Neat -- turns out that for sodium chloride there is extensive literature on this. Ethanol is apparently effective as an anti-solvent, but various dimethylisopropylamine compounds appear to be more effective and are used in industrial settings.

Interested now to try this experiment but with ethanol to better control the crystal formation.

Wonderful! I was tempted to do some searching on ethanol, acetone, any volatile things that are generally available... good to know ethanol is effective.

Will be a fun xmas experiment to do!

That's really clever. How long did this process usually take, what size crystals were you going for? And were these crystals ever visually interesting, or do most organic compounds just form colorless little prisms or cubes?

"Sadly" (not for me back then) a crystal 1 mm on a side is more than plenty for structural elucidation. They were only ever pretty to me because

A) you sometimes spend weeks working on the materials that go into the solution, seeing them feels like a "my god finally" kinda thing

B) under a microscope crystals are especially beautiful, even small crystals. We had a microscope set up in an inert atmosphere for sensitive compounds, see eg.


About timing: this could take anywhere from days to months... really dependent on how fast you can go without making ugly intergrown xtals, on how well you select solvents, etc. Experimental science can be cruel.

The rest of the content on this website is simply amazing. I'm so glad stuff like this is still out there on the internet. Nothing clickbaity or exploitative, just really detailed instructional knowledge on an interesting niche subject.

Check out his copper sulfate crystals if you want something really visually impressive: https://crystalverse.com/best-way-to-grow-copper-sulfate-cry...

I wish there was a directory of sites like these.

Marginalia returns sites like these: https://search.marginalia.nu/

Copper sulfate crystals grow huge. I'm fairly certain this was included in one of those DIY kits that took weeks / months to grow.

Just a footnote. Remember that copper sulfate are highly poisonous to molluscs, fishes and crustaceans, and could kill pets also, so if you have it, store the stuff and saturated solutions in a safe place and -don't- discard it in the sink.

Can you imagine that guy's place, with crystals growing everywhere?


I know what I’m doing this weekend with my crystal-obsessed daughter and the bag of copper sulfate I forgot on top of the fridge.

I think the best part is not the recipe itself, but the error handling of the article. It goes into detail into what conditions are optimal, what kind of tools to use, how various mistakes look like (with photos!).

Calcium tartrate is a great high speed introduction to crystal growing because it is very forgiving and "magical." You can get ~millimeter size crystals in seconds. Then once you're hooked you can try growing crystals that require more patience/technique. If you ever saw the demonstration of lead (II) iodide precipitating from solution [1], this demonstration looks similar except that the crystals are sparkly and colorless instead of sparkly and golden.

You'll need potassium hydrogen tartrate (cream of tartar), sodium hydrogen carbonate (baking soda), and calcium chloride (sold as DampRid or Pickle Crisp).

Add a spoon full of baking soda and a spoon full of cream of tartar to a glass of distilled water. They should fizz together as the baking soda neutralizes the acidity of the cream of tartar, releasing CO2. This is what you want, since the mixed neutral salt of tartaric acid is more soluble in water. Stir and wait for the fizzing to die down, then gradually stir in small portions of more cream of tartar until the additions stop dissolving. Let the solids settle in the glass.

Meanwhile, dissolve a spoon full of calcium chloride in a second glass of water. It should dissolve readily with a bit of stirring.

Once residual solids have settled in glass one, decant the clear liquid into another glass.

Now pour the clear decanted liquid into the calcium chloride solution with stirring. Within seconds, you should see sparkling needles rain out of the solution. These are your crystals. The transition is especially striking in direct sunlight. The crystals can be saved and seem to remain stable in air regardless of ambient humidity.

I unfortunately have not seen this demonstration written down elsewhere so I can't offer a citation. I came to it by personal experience when I was on a crystal growing kick as a kid. (Though it may well have been written down somewhere that I have never come across.)

[1] Like in this video: https://www.youtube.com/watch?v=AO67MnZaAvQ

Potassium bitartrate is also a great introduction to crystals.

Get a bottle of good red wine, 2010 or thereabouts. Uncork and drink it. Now look at the bottom of the last glass, if you still can, and - voila - potassium bitartrate.

If you don't find any, don't despair and try another bottle.

Finally some instructions I can follow!

Search for «Rochelle salt piezoelectric crystals».

Here's a project where Rochelle salt can be crystallized to get a piezo effect.


The sodium carbonate needed is otherwise known as "washing soda" in addition to being called "soda ash".

Do you know how safe the resulting crystals are to handle?

If you rub them in your eyes hard enough, you can badly injure your corneas. Maybe if you're really creative you can find some other way to damage yourself with them, but that's all I can think of. Tartaric acid can be toxic at 2000 mg/kg or so, but calcium tartrate is much less soluble, so even much larger doses are probably safe.

I believe that they are safe to handle. None of the compounds or elements involved are toxic at moderate doses even if ingested. I personally handled these crystals with bare hands many times.

> with bare hands many times.

That's how my dad and grandfather both contracted a very specific benign bladder cancer. From having their hands in a solvent without gloves. ):

Just curious, which solvent?

It was likely MEK or maybe toluene. They had their hands in everything and had to scrub them at the end of the day with pumpice, but the grease never came out completely.

> Indeed, table salt is often used in kids’ experiments to demonstrate crystallization. It’s a simple activity, but the results are disappointing.

I remember this was one of the things I tried countless times as a kid. It never worked - the books showed these nice, clear crystals but all I ever got was a crust of dried salt and maybe one tiny crystal a few mm across.

I'm sure most of those "science for kids" book authors never tried a single one of their experiments.

i tried a similar 'experiment' once with sugar to make rock candy, failed the first attempt

my grandma saw and told me to use the rest of the string and sugar I had, enough for 12 more tries, and do them at once but in different areas of the house

only two actually grew but i learned the value of spreading risk and unknown unknowns ( much later, on reflection :) )

We did a rock candy experiment in 6th grade and probably attempted it a few separate times, specifically because we kept having issues. I think at least one batch got moldy. But, if I'm remembering correctly (this is over a decade ago), we may have been placing the dishes near where sunlight hit, so that could've been part of it.

Did this as a kid as well. When I got to high school chemistry, we did an experiment on super saturation of the sugar. Much better results, much faster!

hehe I did that super saturation thing as a kid. one of the instructions was pour until saturation happens. It didnt. I ended up with 5 pounds of rock candy.

Did you do the version where you let the super saturated solution cool down slowly, and then drop a single grain of sugar into it?

That was the plan. But never got to the 'super saturation' point where it would no longer melt in. Knowing what I know now I figure the temp was too high. Least I got an A as I had pounds of crystals. We added flavoring and coloring to some of it and gave most of it away.

When I wanted crystals for microscopy, I made a mother liquor by pouring an enormous amount of sugar in a tiny amount of water (beyond saturation) and then just let the solvent evaporate in a heated chamber.

Made big rocks. https://en.wikipedia.org/wiki/Mother_liquor

Never heard that term before. Not sure I understand the point though. After you supersaturate and then form crystals, the mother liquor is just the left over content that didn't make it into the crystals. What is the purpose of using those remnants?

mainly to get more crystals and as a growth medium for existing crystals.

I'm sure most of those "science for kids" book authors never tried a single one of their experiments.

They should at least recommend distilled water because tap water impurities vary greatly from place to place.

I was expecting distilled water to be the most critical part but it was even mentioned.

Could it be the requirement for "Uniodized table salt"? I don't think I'd be able to find it around here, and I can't think of any good reason someone would have it on hand either.

If you can get "kosher salt," IIRC that should be non-iodized.

> I’m not sure about Kosher salt; it might contain anticaking agents

Diamond brand kosher salt has no additives or anti-caking agents.

If you look for canning / pickling salt, that should be free of both iodine and anti-caking agents.

Have you actually checked your grocery store? Mine sells both iodized and uniodized table salt, in addition to the kosher salt idea that folks have mentioned. I know the OP said that they worried about anti-caking agents in kosher salt and I'm no expert, but I thought they didn't usually have them.

Doesn't iodized salt have a weird taste? I'm pretty sure I don't have any in my house. I don't think reasonably well-off people in developed countries need iodized salt, because we get enough iodine from our diets.

It wasn't long ago when most of Europe was iodine deficient. It got better recently because of a concerted push towards universal salt iodization but there are still some places that remain iodine deficient, including Germany.

* Europe is Iodine Deficient (2003) https://www.thelancet.com/journals/lancet/article/PIIS0140-6...

* World map of iodine status (2021) https://www.ign.org/cm_data/IGN_Global_Scorecard_MAP_2021_SA...

* The Krakow Declaration on Iodine (2018) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6140595/

> Doesn't iodized salt have a weird taste?


> I don't think reasonably well-off people in developed countries need iodized salt, because we get enough iodine from our diets.

Depends very much on your diet. Lots of fish, milk, other animal products? Probably fine. Otherwise, maybe not so much.

Being from Brazil, where table salt is universally iodized, I have a hard time understanding how in 2021 there are still rich countries out there that haven't figured out a proper iodine fortification program. And we even have some people saying they intentionally prefer non-iodized salt!

On the other hand, there was one time I had to do a short no-iodine diet and it was pain in the ass. I had had to go out of the way to find non-iodized salt and good luck finding any pre-packaged food without iodized salt...

In Poland we have normal iodized salt, but we have uniodized salt just for one purpose - making pickled cucumbers. But our "kiszone ogórki" is not the same as typical pickled cucumbers ("ogórki konserwowe", we have those too). It's more like sauerkraut but with cucumbers. With iodized salt they just spoil.

Maybe you could purify iodized table salt through, for example, recrystallization.

What about dishwasher salt? It's usually 100% sodium chloride.

Dishwasher salt is not actually widely available in the US, since we we generally don't have dishwashers with built in water softeners that need the salt.

Most places either have soft water from their water supply, or people install a whole house water softener, if their water is hard enough to cause problems with mineralizing on dishes.

The salt for the whole house water softener would probably work, but the bags are pretty huge.

> Dishwasher salt is not actually widely available in the US

I am in the Bay Area. I bought some off Amazon no problem. It came from the US too.

> since we we generally don't have dishwashers with built in water softeners that need the salt.

Landlord installed a Bosch dishwasher, which has a water softener. The water is pretty hard (I can see by the shower faucet, and confirmed on the utility website). I'm assuming he didn't bother to import the dishwasher from Europe so it must be available in the US.

Yes, Miele too. All the German brands available in the USA are like that. Salt for them is readily available online and at higher-end appliance stores.

I dont think anyone in the US sells that tho.

What? Why not?

A quick check of Amazon.com [1] turned up a bunch of US-looking products, at least.

[1]: https://www.amazon.com/s?k=dishwasher+salt&crid=X6025PAVFBMS...

The only brand I even recognize is Finish, and they're a UK firm, not American. Technology Connections mentions[1] it's a European thing: "I have never ever encountered one, and I don't think I've ever seen dishwasher salt sold in a store."

[1]: https://www.youtube.com/watch?v=Ll6-eGDpimU&t=2098s

> The only brand I even recognize is Finish, and they're a UK firm, not American

Plenty of non-american firms sell products in the US. Like... I don't know, Nestlé?

I watched the same Technology Connections video. He does mention Bosch dishwashers by name. Those are available in the US. It's just that people barely bother understanding how dishwashers work, let alone _very infrequently_ refilling the salt. Heck, people drive without checking tire pressures, dishwasher salt has no hope.

Not surprising that most stores don't bother. It lasts forever too.

They're pretty rare. I stand by the claim that I've never seen a physical store selling diswasher salt. Before I saw that video, if you told me to get some dishwasher salt at the store, I'd have asked if we also needed any headlight fluid or elbow grease.

If it 'lasts forever' I suppose your water really is so different that it being unavailable/uncommon is justified.

Perhaps get a 20kg / 40lb bag of pool salt for $20.

I’m not sure about purity or anti-caking, although some brands are advertised as high purity. You can even get it delivered in the US: https://www.amazon.com/s?k=pool+salt

Perhaps look at the 20kg bags of food salt sold at wholesalers, which might not be iodised. I recall seeing one at a Chinese store, but I’m in New Zealand, so I’m unsure about the US.

'twould appear that non-iodized salt is used in cheese making, so maybe salt labeled as cheese making salt might work.

The article says that iodized table salt doesn't work, and isn't optimistic about kosher salt either.

I used to enjoy growing crystals when I was a kid. It's a good indoor activity for the winter.

Plain white sugar is also interesting. Alum (used to make pickles, can often be found in the herb and spice aisle at the store) makes neat crystals.

If your kids are old enough to be trusted not to eat the experiments, copper sulfate (used to kill roots that are growing into sewer lines) makes beautiful crystals. It can be found at Home Depot-type stores.

Edit: I see this author has a link to another article on growing copper sulfate crystals down at the bottom of this article. Recommended!

> If your kids are old enough to be trusted not to eat the experiments, copper sulfate (used to kill roots that are growing into sewer lines) makes beautiful crystals. It can be found at Home Depot-type stores.

I had a chemistry set as a kid, it had copper sulfate. The only crystals I've managed to grow :)

I was trying very hard to remember what the other two "classic fun-for-kids crystal growing" chemicals were and it was eating me alive.

Thank you for the answer, I still remember my alum crystals for the grade school science fair.

Alum crystals in a disposable pie pan on a hot water radiator turned out brilliantly in my youth.

Fast-forward many years, and my daughter wasn't having much luck with salt, sugar, or even copper sulfate (that one looked like a melted smurf).

I remembered my alum crystals, which she tried, and lo and behold...nothing! Desperate (on the night before the assignment was due), I remembered someone mentioning that you can make crystals with mothball flakes. We picked a bag of flakes up and heated them up in a dish, and were able to make long, beautiful crystals on the bottom of a cold glass over the heated solution.

The only problem was that as soon as we moved the glass away from the solution, the crystals evaporated, so she took a picture of the crystals as they were forming and received full marks. A happy ending, but the house smelled of mothballs for a few days!

I tried Epsom salts as a kid, since there was some around the house. They were a lot easier to grow than table salt.

Epsom salts! Yes! Another good one.

Crystallography, the study of crystals and the structures of their constituents, is fascinating. I work in a field where making crystals like this is so tough that people spend millions of dollars on robots and reagents that just sit around trying every possible combination of temperature, concentration, and other parameters, just to make crystals with high enough quality to do structure determination.

Some crystals just never form. I know folks who spent 7 years trying to get their protein to crystallize and left grad school with a masters degree instead of a PhD because they failed, no fault of their own.

I know in 2D there are patterns that tile aperiodicly, compare https://en.wikipedia.org/wiki/Aperiodic_tiling

If the same holds true in 3D, maybe some of these proteins simply do not form crystals.

Sucks to be a PhD student hitting such a protein.

Looks really good. My three chemicals for crystal growing are



and MKP


and Alum


but probably table salt is cheaper..

Those monopotassium phosphate crystals look gorgeous! Any tips for places to buy that salt?

6 years ago on eBay 2 kg for 30 USD from UK to continental Europe. 2 months ago on Amazon 5 Kg for 43 USD delivered in Europe. It's a fertilizer so it's not supposed to be expensive

Careful using Xerox scans to create your posts...

There's also "salt pyramids" [1] which are desired in Culinary field for their look and texture. Be pretty cool if there was a way to grow a transparent salt-pyramid.

[1] https://www.youtube.com/watch?v=FVEZuzEHwQk

There's a section about pyramids in the article: https://crystalverse.com/sodium-chloride-crystals/#saltpyram...

That's indeed a pyramid, but the video in the OP is referring to "hopper crystals" which are hollow and hence have different culinary uses vs. regular salt.

I'm glad you linked to the Adam Ragusea video, you saved me the trouble of finding it.

I really like Adam's videos, he does a ton of research, and has a very descriptivist approach to cooking in general

NaCl is a lensing material in the LWIR bands, this could lead to very cool applications for cheap thermal cameras

I’m intrigued, but no nothing about lensing materials or the LWIR band. Care to expand or link to a good resource for learning more?

FLIR has a good handbook on some of the physics: https://www.flirmedia.com/MMC/THG/Brochures/T559243/T559243_...

The rest is light transport, e.g. lensing via index of refraction: https://courses.lumenlearning.com/boundless-physics/chapter/...

Here's a cool article on a piece of an old spectrometer: https://utsic.utoronto.ca/spectroscopy-beyond-the-visible-sp...

More information from a distributor of optics: https://www.knightoptical.com/stock/default/windows-and-diff...

Assuming these are edible when complete? I could imagine these for fancy dinner parties where each diner gets a crystal and a small cheese grater

Seems like it is edible given the only ingredients to start were salt and water. I don't know about the durability though. Do these break easily or are they very dense?

Guess we gotta grow some!

I don't think a cheese grater would work? A hammer would be the tool I would go for.

They make salt graters that look very similar to cheese graters. I have one I use with a big block of salt.

I’m ashamed to confess that licking those pretty cubes was the first thing that passed through my mind.

Hey, no shame! A friend gave me a natural halite (salt) crystal that has beautiful purple coloration from natural radiation. Not radioactive, but purple mainly due to displaced electrons that formed color centers. It had great sharply defined edges and faces. For awhile.

When visitors remarked on the specimen, my wife often explained that it was a natural salt crystal. Nobody could resist licking it just to be sure.

Still got a beautiful color, but it's got about the same feature definition as a gummy bear...

It's ok, I too had the immediate though of licking it. "hmm I wonder if licking a flat salt cube is more satisfying than just normal salt..."

"If it looks like picture 4 or 5, let it grow anyway. "

Anyone got a location on picture 5?

It should say "If it looks like picture 3 or 4, let it grow anyway."

Parents! Are your teens getting into "salt"? Know the signs.

What a fantastic article! I didn't know it was possible to grow crystals like that from salt. Have to try this!

Wow thanks for sharing this. Have always wanted to do this ever since I read the first blog on growing crystals [big time procrastination there]. Please share your experience and steps if any for other salts. I am super interested in the blue of Copper sulphate.

These are beautiful. Seems that a possible solution to the problem outlined at the end of the post (they are not quite cubical, but flat) would be to gently flip them a few times during the months they are growing.

Welp, this is a silly project that I have no choice but to try. Looks straightforward and rewarding with a nifty end result.

This is a content-less comment but... great article, thank you for submitting.

Is it possible to grow crystals in moulds to give them custom shapes?

Yes! The turbine blades in jet engines are single crystals of typically Ni or Co based alloys that are grown in a mold. It’s more of a directional solidification process though, I don’t think you could grow a NaCl crystal from solution like this in a mold


You can influence the shape, I'm sure, but the geometry is mostly dictated by the molecules. These cube shapes are just how NaCl "wants" to bond, while other molecules may form hexagonal prisms or other shapes.

Once, I accidentally grew a bed of salt crystals in a plastic tumbler left on a windowsill. Sadly I can't find the photos but they were closer to rectangular and clearer than the "bad" examples mentioned in this post. Diameters reached ~500mm on the large ones. Was I vastly luckier than I realized at the time, or is it all a bit easier to get right if you're not aiming for completely freestanding crystals (vs. a bed)?

Were the conditions significantly different from what the author described? I would imagine if it was relatively cool but also humid, you may have just matched good conditions for growth.

So you probably did get lucky, but depending on the conditions maybe not extremely lucky.

Ok I need to know.. how does one accidentally grow half-a-meter crystal? And how much does that weigh? And what kind of plastic tumblers do you have for that? :D

This makes me curious, and I googled a bit trying to find how large you can grow these transparent, cubical crystals.

Largest I was able to find was about 2cm to a side, maybe a bit less.. Is there any fundamental reason they don't get bigger than this/lose transparency and form as they grow larger, or is it more that no-one bothered doing growing them larger than that?

This is a really cool write up and really intrigues me, on the topic of crystals. I admittedly have very little knowledge or frame of reference on the topic. But there is something very cool about the idea that you can ‘grow’ crystals, like they are little house plants, or that they are like little living creatures or something.

Outstanding instructions. And explains why my earlier attempts failed eg. using string. I'm gonna do this with my kid

> it will probably double in size in a week and reach 1×1 cm in a month

TIL it takes a long time to grow a perfect salt crystal of any size.

I've never seen this before and wonder how stable/fragile are those crystals? Are they very touch-sensitive or can you carry them around easily in your pocket?

I’ve done this as a kid and they’re not really fragile. You could definitely carry it in your pocket.

Dihydrogen monoxide is the key component of this process.

When I was a kid, it was very popular school project to grow copper sulphate crystals. They have a very nice blue color.

> uniodised table salt

Well that ends the experiment for me before it even began. AFAIK by law, all salt sold in my country is iodised.

I guess you could have extra fun and do this: https://www.thefreelibrary.com/Removing+iodine+from+iodized+...

There are lots of other uses for salt where it won’t have iodine e.g. pool salt, dishwasher salt, industrial salt, etcetera.

I have often wondered what sorts of crystals that you can grow at home that are relatively hard, sturdy, long-lasting.

At school we had a sodium crystal that was around 15cm in diameter.

A teacher said, they found it in the woods.

I assume they were being sarcastic? Unless I'm missing something, such a crystal couldn't survive the humidity of the woods for long.

Possibly an artificial "salt lick" [1] that got displaced from its original position.

[1] https://en.wikipedia.org/wiki/Mineral_lick

That's what I said, sodium chloride... sodium chloride... that's what I said...

I'd like instructions for growing quartz crystals at home.

Natrium chloride

Sodium chloride

looks like a fun a project to work with kids


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