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Tom Fine wrote:

> Now, one precaution I take is to clean each disc with isopropynol and a 
> lens cloth, wiping in circles very gently. There are numerous 
> fingerprints on them and we have discussed that in many cases, 
> fingerprints stymie error-correction that can "see" through numerous 
> scratches.

Isopropanol should be safe, but I'd recommend trying water first - it's 
less aggressive and usually sufficient. More important, radial movements 
are far less risky than circular. Any radial scratch will slightly 
affect many samples, but under normal circumstances each will be well 
within ECC capability. Circular damage will affect fewer blocks, but any 
one block is far more likely to have enough errors to fail.

Durability is one of the virtues ascribed to optical media from the 
beginning and is supported by vast amounts of anecdotal evidence. 
Failure of home-made recordings subjected to high temperature and/or 
sunlight is well understood; the chemical changes can even be seen in a 
simple experiment. Using a new disc with blue dye (e.g., Taiyo-Yuden), 
place it dye up in the sun and cover half the disc with a card or other 
opaque object. An hour's exposure in Southern California summer sun was 
ample to bleach the dye unmistakably.

Mike
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