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

[Graeme Jaye <gjaye@retemail.es>]

Ed H. Zwaneveld wrote.......

e> It is also known that polycarbonate media are sensitive to e>
e> chemicals and solvents, and should not be exposed to water which e>
e> they readily absorb and which causes such discs to lose their e>
e> flatness as they absorb water and warp.

Having ground and polished more CD's than I care to count, I thought I
should like to pitch in to this discussion - from the point of view of
someone actually using grinding and polishing processes on optical
discs.

All the effective grinding systems, which I have ever seen, involve
the use of water to transfer the heat away from the disc and to stop
the grinding wheel loading with polycarbonate powder. This is the
first time that I have ever heard any mention that polycarbonate is
hygroscopic.

I don't have the benefit of the specialist tools required to measure
it, but I can positively state that, for *non-archival* purposes, I
have never experienced a disc losing flatness to the point where it
will not play after such treatment.

Similarly, I have never undertaken BLER tests on such discs.  However,
if it is a case of making a non-playable disc work, then these systems
are fully meeting the claims made for them.

e> So until it has proven itself by means of daring guineapigs who
e> have taken the risk, I remain skeptical.

I have many discs, in my own collection, which have been deliberately
damaged and then repaired - some more than once.  They all play
perfectly - at least as far as a simple listening test reveals.

e> The next thing I did was to explore the marketing literature of a
e> purveyor of disc polishing hardware. I read in it that the
e> 'SkipDoctor' also referred to as 'GameDoctor' (www.skipdoctor.com)
e> sprays the CD with filtered water resurfacing fluid (functioning as
e> a lubricant), followed by radial polishing to repair any blemishes
e> in a single or multiple pass, followed by drying the CD with a
e> cloth that is provided and using a felt buffing square to restore
e> the disc's shiny finish. 'It enables you to re-condition just about
e> any blemished disc in about five minutes' says the publicity. So
e> you take the risk of causing a disc to lose its flatness and suffer
e> unbalance afterward, although its scratches may disappear.

As the Spanish distributor of this device, I think I am qualified to
pass comment.

Firstly, there is no practical difference between these models, they
are merely targeted at different market sectors.

Secondly, it has to be borne in mind that this device is not aimed at
archival experts, but to the 'man in the street' whose audio CD
refuses to play properly or whose PlayStation game has ceased to
function.

This is an important distinction to make.  Archivists might worry
about an optical disc maintaining specified flatness, but the
SkipDoctor customer doesn't care about that - as long as the repaired
disc works, he is a happy man.

The water is required, not so much as a lubricant as to stop the
grinding wheel loading with plastic.

In fact, the buffing process, while serving to make the disc look
better is not absolutely necessary.  Many discs will play accurately
enough without going through this stage.

e> Smart Computing (December 1999) has tested the polishing device on
e> two damaged audio CDs. ....'that it actually works pretty well,
e> although it can't perform miracles'. The do-it-yourself unit costs
e> US $ 34.99.

Anyone who *expects* miracles for 35 bucks is bound to be
disappointed.  Personally, I have been amazed at the degree of damage
which people have managed to repair with one of these machines
(albeit, with a lot of elbow grease thrown in).

We have games hire shops who rely on nothing more than a SkipDoctor to
repair their damaged discs. (Anyone who has seen the sort of damage
that kids can deliberately inflict on a games disc will realise just
how important that statement is).

You don't say which Japanese machine you saw demonstrated - I only
know of one - but there are two manufacturers of such equipment in the
USA, We also distribute the products of one of these companies -
CDRepairman - which are far more industrial in nature compared to the
SkipDoctor.

The Fix-a-Disc range of grinders uses water in far more copius amounts
than the SkipDoctor.  We have used this machine to repair many discs
of all types and containing all sorts of data.  We have also sold
machines to others for the same purpose.  At the sort of prices these
machines run to, only someone with a great many discs would even
consider purchase, so it is reasonable to assume that a great many
discs are now in circulation which have been repaired by this process,

Once again, I have never observed, nor had any report of a disc losing
flatness to the point of being unusable - and, to be fair, as long as
the disc *was* usable, no one would ever consider this aspect.

e> Warning: Keep in mind that only the playback side (opposite the
e> label) can be polished.

True - label side damage is irreparable.

e> Some users have indicated that when the disc gets wet, the label
e> ink may run (depending on the kind of label printingink that was
e> used)

Nearly all discs which are subject to this sort of treatment are
commercial in origin.  Obviously, one wouldn't expect commercial
labels to run if they get wet.

e> , and the lacquer may come off.

I have no experience of this occurring.

e> Another concern I have is that the lacquer that protects the outer
e> and inner edges can be ground off on the edge with the polished
e> surface and thus open up those surfaces more quickly to oxygen and
e> oxidation, than would have been the case if the lacquer would have
e> been left intact.

Without having conducted specific tests for this particular aspect,
you may have a point here.  However, I have discs here which were
subjected to very heavy grinding some years ago - and they remain
perfectly playable, with no sign of the reflective layer oxidising.
Since these discs belong to me, I have a vested interest in them
remaining that way :-)

e> On the other hand, discs that are used and circulated are bound to
e> get scratched, and polishing may extend their life.

There is no 'may' about it.  Provided the label side is intact, then
ridiculous degrees of play-side damage can be repaired.

My standard 'demonstration' consists of placing a disc, play-side
down, on the floor and then rotating my foot on it (bearing in mind
that floors here in Spain are almost invariably tiled). Such treatment
is guaranteed to stop any disc from working (the label side is
protected before trying this trick).  The disc is then ground and
polished and shown to subsequently work - in the case of audio discs
(which are the easiest to demonstrate) on the cheapest player we can
find.

Generally, while I appreciate there is a vast gulf between our clients
and the archival world, what other solution do you have for the
problem?

If a CD is scratched to the point of being non-usable, it can be
repaired.  If you are seriously worried about the (possible) longer
term effects of the repair process, then a copy of the now-working
disc can always be made.

Graeme Jaye

gjaye@retemail.es

Audio Restoration and CD Repair
http://www.personal-cd.com