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How to grow sodium chloride crystals at home

by kdavis on 11/17/21, 4:54 PM with 180 comments

  • by fcatalan on 11/17/21, 5:47 PM

    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.

  • by isoprophlex on 11/17/21, 6:31 PM

    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.

  • by voldacar on 11/18/21, 12:41 AM

    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...

  • by philipkglass on 11/17/21, 8:21 PM

    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

  • by avian on 11/17/21, 5:39 PM

    > 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.

  • by Turing_Machine on 11/17/21, 5:57 PM

    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!

  • by seanalltogether on 11/17/21, 5:48 PM

  • by dekhn on 11/17/21, 9:43 PM

    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.

  • by ttoinou on 11/17/21, 7:43 PM

    Looks really good. My three chemicals for crystal growing are

    ADP

    https://en.wikipedia.org/wiki/Ammonium_dihydrogen_phosphate

    and MKP

    https://en.wikipedia.org/wiki/Monopotassium_phosphate

    and Alum

    https://en.wikipedia.org/wiki/Potassium_alum

    but probably table salt is cheaper..

  • by legohead on 11/17/21, 6:12 PM

    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

  • by alhirzel on 11/17/21, 5:37 PM

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

  • by invalidusernam3 on 11/17/21, 7:39 PM

    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

  • by ulzeraj on 11/17/21, 10:18 PM

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

  • by Borrible on 11/17/21, 7:36 PM

  • by dylan604 on 11/17/21, 6:02 PM

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

    Anyone got a location on picture 5?

  • by leoc on 11/17/21, 8:31 PM

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

  • by thunderbong on 11/17/21, 5:37 PM

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

  • by kunalpowar1203 on 11/18/21, 4:12 AM

    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.

  • by djrogers on 11/17/21, 5:25 PM

    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.

  • by jrockway on 11/17/21, 10:26 PM

    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.

  • by ffhhj on 11/17/21, 7:16 PM

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

  • by alexfringes on 11/18/21, 5:54 AM

    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)?

  • by amarant on 11/18/21, 2:45 PM

    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?

  • by 40four on 11/18/21, 2:51 AM

    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.

  • by scrubs on 11/18/21, 1:48 AM

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

  • by rbobby on 11/17/21, 5:38 PM

    > 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.

  • by mh-cx on 11/17/21, 6:53 PM

    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?

  • by SergeAx on 11/18/21, 2:14 PM

    Dihydrogen monoxide is the key component of this process.

  • by skocznymroczny on 11/18/21, 2:48 PM

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

  • by markdown on 11/18/21, 12:26 AM

    > 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.

  • by at_a_remove on 11/17/21, 9:31 PM

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

  • by k__ on 11/17/21, 7:44 PM

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

    A teacher said, they found it in the woods.

  • by RattleyCooper on 11/18/21, 1:11 AM

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

  • by foxfluff on 11/18/21, 11:35 AM

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

  • by beebeepka on 11/18/21, 5:49 AM

    Natrium chloride

  • by jackallis on 11/17/21, 5:30 PM

    looks like a fun a project to work with kids

  • by perth on 11/18/21, 7:00 AM

    salt