Picture of Rochelle Salt
Piezoelectricity is the charge that accumulates in solid materials in response to applied mechanical stress. Substances that exhibit piezoelectric properties to a greater or lesser extent are crystals (Tourmaline, Quartz, Topaz, Rochelle salt and sugar cane), certain ceramics and biological matter such as bone, DNA and various proteins. Quartz and Rochelle salt exhibit the greatest amount of piezoelectrical properties and since the ingredients and instructions for making Rochelle salt are relatively straightforward I decided to make some to play with. I found some helpful guides here and here, but diverged from both guides several times without ill effect. Here are my instructions for making Rochelle salt (Potassium Sodium Tartrate), which yielded at least 5 tablespoons full of the salt and several large single crystals in a few days.

I've recorded two mechanical force tests of a single crystal using both a digital and analog oscilloscope here.

Step 1: Making Washing Soda

Picture of Making Washing Soda
The recipe calls for cream of tartar (Potassium Bitartrate or Potassium Hydrogen Tartrate) and washing soda (soda ash or Sodium Carbonate). Cream of tartar is a byproduct of winemaking; as the grapes age this acidic salt forms on the barrels of wine and is collected and used in a variety of household purposes, from preventing sugars from crystallizing to an ingredient in baking powder to stabilizing egg whites in recipes. Washing soda is highly alkaline (pH of 11) and often used as a water softener. It can be extracted from the ashes of plants and is sometimes used to make German pretzels. Washing soda can be made by heating baking soda (Sodium Bicarbonate or Sodium Hydrogen Carbonate) in an oven to break and evaporate the bonds of hydrogen to leave the Sodium Carbonate.
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ForrestDeep made it!1 month ago
I used store bought washing soda from an art supply store. I let the solution cool at room tempetature and stirred constantly at a leasurely pace.

Instead of forming crystals on top, the solution began to set up like concrete on the bottom of the glass container while I was stirring. The liquid was opaque, but I could hear and feel my spoon scraping against the growing rock. When I finally poored off the liquid, the rock was about a centimeter thick, with a pitted, uneven surface.

I tested the rock with a volt meter and it did show more voltage when I pressed harder with the probes

I don't have a pix on this device, but I will come back and include one tomorrow. For now, here's another picture to enjoy
danja.mewes3 months ago
These instructions don't seem to work for me. 7 hours later I still have a clear liquid in the fridge, no crystallization. Other instructions seem to think 2 hours at 300 is not enough to result in washing powder and suggest 4 hours. I think just adding that directly to the cream of tartar in simmering water also isn't echoed by other similar instructions. am I missing a step? If I added too much of the powder, would it still crystallize if additionally saturated (that's the only place I could've gone wrong, even had a helper chemistry student)? Any ideas or suggestions why im not seeing crystals?
Could someone please help me?! I made the solution and it has been on the refrigerator for more than a day, it has only become very dense and I need those crystals ASAP!!! Can someone tell me if there's something wrong with it, should i make more, is it a matter of time...?!?!?! Please!

Put it in a less cold place.

bobdabiulder made it!3 months ago
Is that made right?
indigo-dog6 months ago

Is it possible to generate enough electricity to light up a LED using the crystals? Connecting them in series or with some capacitors?

I have a question. What generates more energy? PZT or Rochelle Salts?


can one influence the growth of such a crystal electricity, like a pulsed dc signal being sent through it?

Thoth1 year ago

At this step you are not reaching saturation but rather neutralization of the the cream of tartar solution that is why it stops fizzing (i.e. giving off CO2) after a certain amount of washing soda.

mdagn1 year ago

back in the 1970s cheap crystal earphones using "rochelle salt" were commonly available in electronics shops so I did know of it a long time ago .. but until now had no idea what rochelle salt is actually made of ... I only knew it was strongly piezoelectric.

another material you could probably try is PZT salvaged from a cigarette lighter

(the ones that use a small electric spark to ignite the gas)

boardsmm1 year ago

Fantastic! Can I ask, what does "9.6v after being tapped" mean? Does it mean it genereates a single pulse? What happens if you press it for a longer time?

...and how is there any polarity in this, I mean where exactly do you measure?

Thank you!!! :-)

emdaniels (author)  boardsmm1 year ago
"9.6v after being tapped" means physically hitting the crystal. The mechanical force to the crystal presses the structure together momentarily against it's polarity, forcing it to realign, and in doing so it releases energy in all directions.
One of the most awesome things i have seen so far, piezoelectricity here i come! thanks emdAniels
NealKipper1 year ago
Congrats! You clearly put a lot of effort into this!
snotty2 years ago
This is awesome! Maybe I'll screw around with these and see if I can't make mats with LEDs that light up when walked upon.
I think crystals are the technology of the future, simply because all known reality is composed of vibration-see Maxwell's Equations. Even solid matter is not solid. Therefore, certain crystals should do some pretty interesting things when resonated at the right frequency.

Thanks for posting your project.. I must try it some time.
gabdab3 years ago
Could you use it somehow inside wind turbines to replace generators ?
Sh3nrA3 years ago
If you guys like this you should check out John Hutchinson's Crystal battery using Rochelle salts. its pretty cool
2xlbu4u3 years ago
Whoa.. I was just thinking that It's so inexpensive to make. What if you were to create a large slab and place it in-between 2 concrete slabs the size of a single lane highway. You could put small grooves in the top slab to induce vibration as cars passed over it (like a rumble strip). Make enough for at least a ¼ mile and wire them up in series / parallel (figure out what will give max power). Anybody know why this won’t work ? Maybe the useful life of the crystal is too low and it will just shatter after a short time. If that is the case, maybe you could introduce an inert polymer into it to maintain structural integrity. Gosh if only I didn’t have a day job and limited funds or I’d be trying it right now 
emdaniels (author)  2xlbu4u3 years ago
That would be pretty cool! Unfortunately it's really brittle so it would most likely break from the pressure. You'd probably want to sandwich it between sheets of conductive foam to cushion it and catch the electricity generated. You should try it!
my mother wants to know if you color Rochelle Salt if you added food coloring? anyone know?
emdaniels (author)  lookwhatjoeysmaking3 years ago
Haven't tried with food coloring yet! A quick search of google doesn't come up with a lot of info for it either.
Congratulations on your win! I'm front Ottawa as well =)
emdaniels (author)  EngineeringShock3 years ago
Thanks! You should come to the Mod Lab maker meetups at Artengine! Great group of people there. :)
i tryed makeing some using collins video but it stoped fizing and it wasnt cleer it was yellowy color any idea why?
emdaniels (author)  lookwhatjoeysmaking3 years ago
Regarding the yellow color, I might start by checking the purity of the cream of tartar. There are some manufacturers that sell cream of tartar with filler to reduce costs. I heard that McCormick brand sells a good cream of tartar, but I haven't tested it.
cool thank you for the speedy reply.
Brilliant ! have not come across this compound before, even though I have experience in crystal growing -much [ trial and error]:-)

Your recipe is very reliable, I do however have a ? Washing soda [na2co3.10h20] is a very accessible chem. Your calcination? method is logical but energy dependant? Na2Co3 has an R.A.M of 106.0 the decahydrate is 286.0 =[2.7]

if you use same proportions but use same scoop for both chems it work out well

Apologies if I am Saying what you are already aware of:-0
emdaniels (author)  inspecter gadget3 years ago
Thanks inspector gadget! It's true- both will work out well. I didn't have access to the Arm & Hammer Washing Soda or any other decahydrate washing soda from a store so I had to make my own. If you can buy washing soda and want to skip the steps of making it yourself it should still work out fine.
I Made Far Too Much Of The Stuff Then I Needed -But With Selective Growing There The Size Of Alum Crystals.
Kiteman3 years ago
I'd like to see how you mount or connect these crystals to actually tap into the voltage generated.
emdaniels (author)  Kiteman3 years ago
I just added two mechanical force tests of a single crystal using both a digital and analog oscilloscope to my website: http://www.emilydaniels.com/2011/11/further-testing-of-rochelle-salt/
PierreF3 years ago
Hi! I tried some time ago to make a speaker out of this:

And it worked pretty well :)
emdaniels (author)  PierreF3 years ago
Nice! Thanks for sharing!
kcdoodle3 years ago
wow. This has my head buzzing! Could you make a mini-alternator type generator, like to recharge a small battery for a little radio, or cell phone by putting many small crystals on a wire, and a wheel at equal distances, turn a crank to strike the crystals against a flywheel, to run electrical appliances? How about LED lights? Many options here!
wkoepp kcdoodle3 years ago
yes with some imagination you can construct the things listed. Just keep in mind your results might not be what you expect. Even though stated on this instructable that a crystal could put off 9V it would take a large crystal with a large stressor. there is a reason why these crystal are typically used as sensors allot. The voltage output is too small to run a load but high enough for accurate readings. You might want to look into using it in combination with a BEAM Robotics project.
Hope your ideas are a success though and have fun.
Broom wkoepp3 years ago
Actually, the voltage output is high enough - 9.6 V is more than any USB-powered device uses! It's the current output that's too low to be useful (or, ultimately, the power).
wkoepp Broom3 years ago
Well the voltage out put is roughly 9.5V peak-to-peak AC shown is studies, so the actual rms value (DC volt equalent) will be 70.7% of that of one peak. one peak being 4.25 V max assuming this is a sine wave AC output. The voltage rms there for is 3.35V. This is less than the 5Vdc output of a USB cord. As for current you will need to determine the internal resistance of the crystal as well load resistance apply the total resistance into the ohms law formula and that will give you your current. the crystal itself creates a potentual difference (voltage) not current. you must have a complete circuit to have current.
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