I used to work for years in the chemical business (polymers) and I remember of many high tech and demanding applications (injection moulding of medical parts, fine fibers, ...) for which even minor changes in the polymerisation reactor conditions on a specific supplier product line would impact the final quality of the finished good and make it improprer for use. (change of melt flow, or other physical parameters). So only a very few selected polymer suppliers were approved for specific applications and specific grade quality had to be always delivered according to most stringent controls (lot per lot analysis, treacibility, ...). When adding pigments this makes it even more difficult as getting proprer mixing within the polymer adds to the complexity.

Does anymoe has information on that aspect of the CD production process : polycarbonate grade selection, approval, lot treacabily at CD plants; it could also have implications in the "lot per lot" problems we sometimes notice  on the CD we buy.

Michel Merten
Sound Arts Group/Musica Numeris

Jerome Hartke <[log in to unmask]>
Sent by: Association for Recorded Sound Discussion List <[log in to unmask]>

24/08/2004 00:14
Please respond to Association for Recorded Sound Discussion List

        To:        [log in to unmask]
        Subject:        Re: [ARSCLIST] ? about Burning CDs for archives

CD-R discs are manufactured by injection-molding the 1.2 mm thick
polycarbonate substrate that contains a spiral pre-groove. The dye layer is
then spin-coated on the surface containing the pre-groove. A reflective
layer is then sputtered over the dye layer, and a thin protective layer is
spin-coated over the reflective layer.

"Color" in the polycarbonate layer relates to the visual part of the
spectrum, while the CD laser operates near 780 nm in the near-infrared.
Consequently, the visual properties of the polycarbonate are immaterial.
Modification of the infrared properties of the polycarbonate would degrade
the read/write capabilities of the disc, and is not done.

I do not pretend to be always right, but the above information is accurate,
as a bit of common-sense thought would confirm.

Media Sciences, Inc.

> -----Original Message-----
> From: Association for Recorded Sound Discussion List
> [mailto:[log in to unmask]] On Behalf Of Don Cox
> Sent: Monday, August 23, 2004 1:02 PM
> To: [log in to unmask]
> Subject: Re: [ARSCLIST] ? about Burning CDs for archives
> On 23/08/04, Mike Richter wrote:
> > Arguing this technology with Jerry is about as wise as disputing
> > mathematical physics with Stephen Hawking - except that Jerry *can*
> > communicate when one is not excessively simple.
> Well, Hawking recently admitted to being wrong about one of his major
> theories, after about thirty years.
> I have seen no scientific evidence or tests here, only a blanket
> out-of-hand dismissal of the possibility that there could be any
> advantage. I don't know if there is an advantage, but the extra
> manufacturing cost is small; so if there is an advantage, then black
> polycarbonate would be worth while.
> People who are very certain about something are often wrong.
> Regards
> --
> Don Cox
> [log in to unmask]