rfg@hound.UUCP (R.GRANTGES) (05/13/85)
[] Come on all you wedding guests, out there. The ancient mariner has an instructive tale to tell. I did it. I ruined two cd's by lightly scratching my initials on the <back> of the cd with the tip of a pocket knife. I thought I was barely scratching the surface. And we all know that there is a "protective coating of plastic" over the aluminum on that side. DONT BELIEVE IT. It wouldn't protect the surface from a sharp fingernail. I was aiming to produce a very shallow mark, and in fact you need to look carefully at an angle with light bouncing off the surface to see the scratches. But the plastic is in fact incredibly thin. When you hold the disc up to a light bulb - looking thru the disc at the light - you can see part of the initials writ in the aluminum, where the aluminum was destroyed, and woth it millions of bits of info. Where the scratch is tangent to the grooves is where things reallygo to hell. So the bottom line is: CD's are much more sensitive to scratches on their label side than they are on their laser read side. Polishing won't help because its the bits themselves that are gone. An interesting sidelight is the idea of inspecting CD's like you were candling eggs. You would be surprised how bad some look and yet play. Some look like the starry skies with nearbye planets, others have scarcely a hole. So far two samples of one brand I checked were much worse than any of the other brands. I won't mention the brand because I'm not sure they are guilty, yet, but I'd bet on it. Still the discs play ok - or did until I took out my pocketknife. -- "It's the thought, if any, that counts!" Dick Grantges hound!rfg
karn@petrus.UUCP (05/14/85)
Dick, in the category of "you can't say they didn't warn you", I quote the following from a current series on CD technology in Electronics and Wireless World: "...Conversely, the label side of CD is much more vulnerable, as the lacquer coating is only 30 [microns] thick. For this reason, writing on the label side is not recommended; pressure from a ballpoint pen could cause mechanical damage to the information layer, and solvents from marker pens have been known to penetrate the lacquer and corrupt the disc. A common party piece is to show off the error correction system by writing on the readout side with a felt tip pen. This is relatively harmless as the disc base material is impervious to most solvents." By the way, this has been a pretty good series. It started in the January 1985 issue. Phil
rfg@hound.UUCP (R.GRANTGES) (05/14/85)
[] The current issue of The $ensible Sound, a magazine I used to think was reasonable, holds one manufacturer up to ridicule for announcing that its CDs would have an extra protective coating of vinyl (or something). At the time I fell for it thinking, "Yeah, what a ridiculous, unnecessary idea." Now I know better. -- "It's the thought, if any, that counts!" Dick Grantges hound!rfg
ben@moncol.UUCP (Bennett Broder) (05/14/85)
>I thought I was barely scratching the surface. And we all know that there is >a "protective coating of plastic" over the aluminum on that side. According to the instruction manual that came with my Revox CD player, the back of a CD is *NOT* coated with plastic. The coating is simply a thin layer of shellac, occasionally covered with a layer of ink. The manual goes on to state that although the laser side of the disk can withstand considerable abuse and still be usable, even minor damage to the back of the disk can render it unplayable. I guess you scratched your initials into the wrong side. :-) Seriously though, I would think the only 'safe' area would be that area near the center of the disk that is clear plastic on Japanese disks. Ben Broder ..vax135!petsd!moncol!ben ..ihnp4!princeton!moncol!ben
rfg@hound.UUCP (R.GRANTGES) (05/14/85)
[] Not having a Revox manual, I relied on various explanations I had read in the literature, some of which, I'm sure came from sony. -- "It's the thought, if any, that counts!" Dick Grantges hound!rfg
monta@cmu-cs-g.ARPA (Peter Monta) (05/16/85)
Well, all this begs the question, so I'll bite. Why not make the label coating as thick as the other side's, or at least a lot thicker than 30 microns? Is this a fabrication problem? Peter Monta monta@cmu-cs-g ..!rochester!cmu-cs-pt!cmu-cs-g!monta