On Fri, Jul 07, 2000 at 07:00:10PM -0700, Tim May wrote:
> At 12:45 AM +0200 7/6/00, Anonymous wrote:
> >CD-RW and green/blue CDRs are quite UV sensitive. The dye substrate is
> >eaten by UV, and the data is essentially just patches of more/less
> >reflective bits in that dye. Presumably, leaving one data-side-up in the
> >sun for a day or so should render it useless.
>
>
> The scientific method would be to do some experiments.
>
> "Leaving a CDR out in the sun for a couple of days is not a very good
> method for protecting data against snoopers."
>
> A long answer to a trival point, but it aroused my curiosity. Much as
> the claims that EPROMs could be erased with airport x-ray machines or
> inadvertent exposure to sunlight did, and much as claims that
> floppies are easily erased with small magnets. In none of these cases
> is the folk wisdom supported.
At the risk of continuing a somewhat off topic thread, it is my
understanding that the writing mechanism for CD-RWs is basicly thermal
and involves local heat induced changes in the crystaline structure of
the writeable layer induced by absorbed optical power from the pulsed
laser diode in the writer. Erasing CD-RWs before rewriting them is done
by annealing the written area with multiple passes of lower powered
heating from a continuous non pulsed laser diode. This all suggests to
me that perhaps a CD-RW could be erased by heating it in a oven or with
a heat lamp, perhaps only to temperatures that would not otherwise
render it useless by deforming the plastic substrate.
And yes I am lazy and haven't yet tried this.
I did try an experiment with heating video tapes up over the curie
point of the magnetic material once, however...
--
Dave Emery N1PRE, [EMAIL PROTECTED] DIE Consulting, Weston, Mass.
PGP fingerprint = 2047/4D7B08D1 DE 6E E1 CC 1F 1D 96 E2 5D 27 BD B0 24 88 C3 18
