CD Eating Fungus?

From: Pete Turnbull <>
Date: Wed Jun 20 14:48:06 2001

On Jun 20, 10:56, Chuck McManis wrote:

> I had thought it was common knowledge, the reflective layer in many CDs
> sputtered aluminum. When exposed to oxygen (as can happen when oxygen
> migrates through the plastic or the plastic is cracked) the Aluminum
> oxidizes and turns black. It does look a bit like a fungus but only
> it tends to follow the grain pattern in the deposited aluminum.
> Aluminum-oxide is black and quite hard actually.
> I've seen several examples of this in "real life" and while I have never
> seen the process to actually _remove_ Aluminum from the disk it is
> conceivable that the Al02 would form a different crystal matrix and thus
> change its orientation relative to the original sputtering. That could
> leave 'gaps' where the original reflective layer was.

But aluminium oxide is Al203 and it's a white powder. Or a rather
attractive (and, yes, very hard) crystal, known as carborundum, ruby,
emerald, amethyst, etc depending on the impurities :-) The only place
you'd get AlO2 (which is also white/clear, by the way) is as aluminate ions
in solution.

> So folks to don't understand chemistry invent the 'fungus' idea and off
> goes into urban legend-dom.

Pete						Peter Turnbull
						Network Manager
						University of York
Received on Wed Jun 20 2001 - 14:48:06 BST

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