Re: Re[2]: [AV Media Matters] Polishing of CDs

[ggib@LOC.GOV]

Dear Mr. Iraci:

Thank you for your very valuable information.

It is very unfortunate that the manufacturers of the products you
tested have not provided us with such information.

Gerald Gibson
Audio and Moving-image Preservation Specialist
Preservation Research and Testing Division
Library of Congress
Washington, D.C. 20540-4560

>>> <Joe_Iraci@pch.gc.ca> 08/10 10:00 AM >>>
I have performed some brief experiments on CD polishing as part of
the work
that
I am doing on the disaster recovery of CDs.  One of the scratch
remedies
studied
was the Fix-a-Disc polishing system.  Scratched and unscratched discs
were
examined with the results summarized as follows:

Read-only disc with no scratches.
The disc was unaffected by the scratch removal procedure.

Recordable CD with no scratches.
The disc showed an increase in BLER (1.8 to 12.9) and E32 (0 to
43494).
Also, a
3.5 minute portion of the disc could not be analysed at all.

Audio CD with significant scratches and playability problems.
With the scratch removal the disc got worse: BLER (44.6 to 59.9) and
E32
(648 to
84013).  After a long polishing time all the scratches could not be
removed.

Audio CD with significant scratches and playability problems.
This disc showed improvement: BLER (72 to 59.9) and E32 (26332 to
1955).
However, deeper scratches were still evident.

A fifth disc initially could not be analysed but after scratch
removal it
could
be studied.  However, the disc remained in poor shape with E32 at
10799 and
deep
scratches still evident.  Polishing the disc for several hours with
the
highest
grit paper could not remove all of the scratches.

Therefore, from this small study it is evident that polishing appears
to be
hit
or miss.  It may improve scratched discs to some degree but may also
make
discs
worse.  This was especially evident in the unscratched CD-R that was
put
through
the process (as a control).

Some other scratch removal solutions (plastic polishes, metal
polishes,
commercially available polishes for CD repair, and others) were also
tried.
The
results for the mild abrasives were variable as indicated below:

Of the 21 discs tested with the various remedies 33% showed no
change, 24%
showed an improvement and 43% were worse after treatment.
Essentially half
the
time the treatment resulted in a disc that was worse off than the
original.
Once again scratch removal treatment in this way should be used as a
last
resort.

Joe Iraci
Conservation Scientist
Canadian Conservation Institute