Electrets - D'Addario Dark Rosin, Carnuaba Wax, Beeswax 1

This electret was made of a 75mm diameter mix of D'Addario dark rosin (27 grams), carnauba wax (38.2 grams) and beeswax (1.4 grams). I chose this rosin simply because it was what was available, though I was aware that lighter is better and water white rosin (which was not available) is best. The box says it is triple-filtered and contains non-crystallizing American gum rosin, natural beeswax and castor bean oil. The top electrode was 50mm so the effective area should be around that. This electret was made using the technique outlined on the main electret page.

Making the Electret

Available at music stores. Used for putting on violin bow strings and other places.

The beeswax, purchased locally.

Carnauba wax ordered from http://www.eco-house.com/, Eco-House Inc., P.O. Box 220, Stn. A, Fredericton, N.B., E3B 4Y9, Canada, 1-506-366-3529. It was #960 in their catalogue.

The three ingredients before melting.

Making the rosin, beeswax and carnauba wax electret.

I turned on the stove to MED at 4:30pm. Wax temperature quickly rose to 160C so I turned the stove off again. By 4:45pm the wax was at 100C so I heated up the top electrode using a heat gun and put it in place. I turned on the high voltage power supply and set it for 6kV. Initially the oscilloscope showed some low amplitude spiking though there were no arcs and no sounds. After about 1 minute the spiking was gone. While the electret was still cooling, the voltage kept going up slowly so I kept turning it back down to 6kV. It looked solid by 5:00pm but I didn't turn off the power supply until 5:22pm. The bottom of the aluminium bowl was a little warm. I couldn't easily dettach the top electrode so I left it attached and wrapped up the electret.

Result - Testing the electrets

I first tested the electret a few months after making it, as you're supposed to. I don't recall how I tested it but the results were that it didn't work. This can happen since there is a polarity reversal process that goes on and if you test during that reversal process you'll find no charge. I was just unlucky and happened to test while the reversal was still happening and mistakenly thought it didn't work. Six years later I tested it again with my homemade electroscope (see photos below.) This time it worked, the leafs of the electroscope separated when I test both the top and bottom of the electret.

Testing the top of the electret.

Testing the bottom of the electret.

See the testing section of my main electret page for more testing details, including how to test for the polarity reversal.