Re: Plastics question

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Antonio Carlos M. de Queiroz" <acmdq@xxxxxxxxxx>

Tesla list wrote:

> Original poster: "Dave" <dgoodfellow@xxxxxxxxxxxxxx>
> You never know what you will get unless you see the manufacturer's 
> spec sheet on the plastic. Black Delrin works fine for primary 
> forms. Other black plastics may not. I spray painted some plastic 
> primary blocks with black wrinkle paint one time and couldn't get 
> the coil to fire at all, despite everything being in the ballpark of 
> tune. Had to re-make the primary blocks, then the coil worked fine, 
> and that was the only change I made.

It's simple to test materials for high-voltage insulation. Rub a clean
piece in your hair and see if it gets electrized, attracting hair in
your hand. If the electrization occurs, the material is good.
There is still the possibility of the presence of partially conductive
material inside the plastic, as may happen with certain PVC tubes.
And you will see that PVC, unless very dry, fails the test.
A more elaborated test requires an electroscope. Charge it and
touch it with a piece of the material to test. A really good insulator
would not affect the electroscope at all. A conductive material
obviously discharges the electroscope immediately. A material that is
partially conductive inside apparently discharges the electroscope,
but the electroscope shows charge again when the material is moved
away.

Antonio Carlos M. de Queiroz