From: DonRath@aol.com
Date: Mon, 21 Dec 1998 12:52:37 EST
To: pinhole@exploratorium.edu
Subject: Hot Plate Coins Question by Peter Geschke
Peter --
The Hot Plate Coins was one of my activities for the Money Science Saturday,
and there was indeed no write-up (sorry!). Your assumption about a build-up of
oxide films is correct -- the colors are produced by the same sort of thin
film interference mechanism that produces the colors in soap bubbles, oil
slicks and peacock feathers. Part of the light reflects from the front surface
of the film and part from the back, and the two reflected portions intefere
with each other. Depending on the film thickness, certain wavelengths will
undergo constructive interference and others destructive, so the color you see
changes as the thickness of the oxide film changes. I'll quit here, since I'm
already over my 25-word limit! Hope this helps. -- Don Rathjen