I redid this project with some students in a materials science class. They were able to make both the conductive and insulating dough fine. The only variable I could figure out which was different was the type of cream of tartar used; the ones that worked were made with McCormick Gourmet Collection cream of tartar. The ones that did not were made with a QFC generic brand.
In addition, I made some conductive dough from nshima, which is a corn based grain eaten in Zambia. Here's a picture. Insulating dough made only with nshima and distilled water was too conductive to be useful.
I have spent a couple weeks this summer working to evaluate fun and creative methods to teach conductivity and circuits. I worked with both the Squishy Circuits and also with the Bare Conductive Paint. This is a story of success and current failure.
Success Story: The Bare Conductive Paint is an easy to use and very fun tool to lay down electrical wiring. The prototype shown at right is a X-mas tree where one wire runs from the positive battery terminal, up the left side of the tree, and to the anode of the LED. The other wire runs down the right side of the tree from the cathode of the LED to the negative terminal of the battery. The paint is a graphite impregnated concoction (hence the black color), which can be painted on with a brush. It is much thicker than normal paint. My X-mas tree was made on sticky-back green felt which was then affixed to a card.
The inspiration for the X-mas tree was this video from the Bare Conductive Paint website: How to Cold Solder.
Here are a couple christmas presents made for Xmas 2014 for my niece and nephew. I was particularly proud of the Despicable Minion since the battery made a cool eye, and the conductive paths were along the outside profile of the character and then under his overalls.
|Two blobs of green conductive dough allow a circuit |
to be made between
an LED and a 6V battery pack.
Less Successful Story: I have been playing with making conductive and insulating dough using the Squishy Circuits recipes. I really like the potential for creative application of very simple circuits, and in theory the technology is simple enough that I could work with this system in remote locations, such as Zambia where I have gone with a school group for three summers. The doughs are just flour and water mixtures, with salt added for the conductive dough (along with cream of tartar or lemon juice as a stabilizing electrolyte), and sugar added for the insulating dough. The conductive dough works great, as you can see from the picture at left.
|With the brown insulating dough in the middle, the|
LED turns off indicating a short between
the two conductive blobs. Apparently the
insulating dough has lower resistance than the LED.
However, I've had real issues with the non-conductive dough, which seems to short the LED, suggesting that the dough has lower resistance than the LED. I have tried using distilled water, deionized water, and two types of flour (normal bleached and an organic wheat flour), which no discernible differences in behavior. The folks at Squishy Circuits have been really supportive, but can't seem to offer much help in terms of suggesting possible reasons for the issues with the insulating dough. This has been a frustrating project. I'm taking a break from it and will revisit later, possibly using some students in a chemistry class to help troubleshoot in conjunction with a unit on bonding (which relates to electrical conductivity). Check out more on Squishy Circuits on their Facebook page.