Real Sound Cookery – Make a contact mic with baking soda and cream of tartar.

home made Potassium sodium tartrate "Rochelle Salt" crystals chunk in top right is aprox 5mm long

I’ve been into contact mics for a very long time, and have used them to record sounds for my records since 1999. There is something magical about how an innocuous little brass disc covered in ceramic piezo crystals can act as a sonic microscope, revealing tiny sound-worlds easily and cheaply. For a bit more info on contact pickups have a look at some of my previous posts: Shit I’m a Geek / The joy of Piezoelectricity and Leafcutter’s DIY Steel Can Hydrophone & Preamp. Step-by-step guide *schematic link fixed!*

I recently stumbled on a great video tutorial by Collin’s Lab entitled  ‘Homebrew Piezo’ in it he shows how to make Potassium sodium tartrate  crystals also known as “Rochelle Salt”. These crystals are fairly amazing in that they are made from ingredients available cheaply from your local grocery store or supermarket. I suggest you watch it as it shows the process really clearly. Later in this post I’ll show my experience of following Collin’s method and do something Collin didn’t – Made some sound with it!

If you want to make your own crystals you’ll need:

  • 200 g / 7 oz Cream of Tartar (aka Potassium Bitartrate, aka potassium hydrogen tartrate) from the grocer/supermarket
  • about 120 g / 4 oz Sodium Carbonate  (aka soda ash) OR same amount of baking soda (Sodium Bicarbonate) if you cant find the Sodium Carbonate.
  • Pyrex jug or bowl
  • Pan big enough to fit the bowl inside
  • Filter paper or Kitchen towel
  • Thermometer useful but not essential
  • Clean Baking tray and Oven if you are using Baking Soda instead of Sodium Carbonate

The Method is pretty simple, follow Collin’s Video to the letter! If you cant see the video for some reason here are the basic steps:

Collin asks for Sodium Carbonate  (soda ash) in the video, I could not find this but luckily you can make it very easily. Get hold of some Sodium Bicarbonate from the chemist or supermarket and spread it thinly on a clean baking tray. Now bake this for an hour or so at about 150 deg C / 300 deg F stirring the powder every 15 mins or so. Doing this will give of water vapor and Carbon Dioxide (open a window maybe) and after an hour your Sodium Bicarbonate will have turned into Sodium Carbonate!

  1. Using your Pyrex jug Dissolve 200 gr / 7oz Cream of Tartar (Potassium Bitartrate) into 1 cup cold water. Stir.
  2. Pop the jug into a pan of water, turn on the heat until the water bath reaches about 82 C / 180 F. If you don’t have a thermometer the water will start simmering at this point so keep an eye out for little bubbles in the pan.
  3. When the water bath is at 82 C / 180 F put half a teaspoon of Sodium Carbonate into the Pyrex jug and stir, it’ll bubble up and then subside.
  4. When the bubbling subsides repeat step 3. until the milky mixture goes clear (slight yellow tint).
  5. Your mixture is now ready to filter, while still hot pour into another heat proof container (a clean jam jar is good) through filter paper or kitchen towel to get rid of any solids. Don’t mess about here as crystals will form as soon as the mixture cools and you don’t want that happening in the filter.
  6. Place the container in a coolish spot cover loosely and wait for the crystals to form!

This is my solution just after pouring:

 

tiny crystal forming at the botom of the jam jar

 

after 2-3 hours

after sitting overnight

loose crystals fished out of the jar dried and viewed X50

So I seem to have generated thousands of tiny crystals as opposed to a few big ones like Collin managed – not sure why this happened but maybe linked to a fairly short cooling time. I wanted to see if the crystals were in fact piezo electric so I arranged the following rig to hold the tiny crystal against two contacts which were connected to a little battery powered guitar amp.

.

Holding a music box against the clamp I was able to record this sound

Not quite as good as the stuff in my mic drawer but it’s amazing considering it’s made from cookery ingredients!

I’m going to let the crystals in the jars carry on growing and I’ll add another post when I’ve managed to grow a bigger crystal.

Give it a go and let me know how you get on!

J x.

UPDATE – Check out my larger crystals.

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16 Comments to Real Sound Cookery – Make a contact mic with baking soda and cream of tartar.

[…] Real Sound Cookery – Make a contact mic with baking soda and cream of tartar. [leafcutterjohn.com] […]

Tim Rochford
August 22, 2011

Very cool science.

[…] [Leafcutter] is big in to making music and has put together all sorts of musical instruments and tools over the years. Recently, he was inspired to make his own piezo crystals, and wrote in to share the results of his experiments with us. […]

[…] [Leafcutter] is big in to making music and has put together all sorts of musical instruments and tools over the years. Recently, he was inspired to make his own piezo crystals, and wrote in to share the results of his experiments with us. […]

[…] [Leafcutter] is big in to making music and has put together all sorts of musical instruments and tools over the years. Recently, he was inspired to make his own piezo crystals, and wrote in to share the results of his experiments with us. […]

[…] [Leafcutter] is big in to making music and has put together all sorts of musical instruments and tools over the years. Recently, he was inspired to make his own piezo crystals, and wrote in to share the results of his experiments with us. […]

andrew
August 23, 2011

This is crazy! Awesome

100limited
August 23, 2011

great! what next?

concretedog
August 23, 2011

Nice one, I saw the collins video and thought about contact mics then forgot about it…I must try this.

[…] a bash at making larger Rochelle Salt crystals using this method. Initially used too much water and nothing formed overnight. I reheated the liquid and added […]

Maki Naro
August 25, 2011

I too got the fine slush as opposed to the big chunks sitting at the bottom of the solution. Did you ever find a fix? Perhaps Collin was seeding his?

Leafcutter John
August 25, 2011

Yes, I managed to get bigger chunks on my second attempt – pay close attention to the quantities you use. Have a look at my latest post which has method and pictures – http://leafcutterjohn.com/?p=1548

[…] MI-12188A, including instructions for restoring and modifying this 50′s public-address amp. A piezo pickup made literally from scratch. This build doesn’t have a bill of materials, it has a recipe. A […]

Maki
September 7, 2011

Thanks for the reply! I think the problem was sub-standard, possibly cut ingredients. Ordered online by its chemical names and presto, big chunky rocks. Oh, and the piezo crystals came out great too >_>

[…] crystals convert mechanical force to electricity, and vice versa, allowing you to make them into a contact microphone. I ended up with a pretty good batch, giving a bunch to Matt to play with. Here’s a […]

Piezoelectric crystals | MD
October 16, 2012

[…] a Lamp Rack We tested the crystal with a rack. Music Box We followed the same experience from this web page in which the subject to be recorded was a music box. The frequency of it’s vibration is easily […]

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