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#61896 - 11/19/03 01:30 PM
Just a note about CD-R, CD-RW and DVD-R
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Senior Member
Registered: 01/16/02
Posts: 2330
Loc: North Yorkshire UK
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Reading through many of the posts on this forum, it is obvious that many people are now using CD-R or CD-RW to back up data. I thought the following might be of interest.
I read an article some time ago, from an authoritative source, about problems associated with CD labels. It would seem that fixing labels to CDs, can in some cases, affect the life of the data recorded on a CD-R. The problem is apparently caused by the chemicals in the adhesive on some labels, gradually leeching through the upper surface of the CD and affecting the dye layer, on which the data is recorded. I only use 'PRESSIT' labels and when I read about this problem, I contacted the firm and asked for their comments. They replied that they had not experienced any problems associated with their adhesive and that all materials used in their labels were benign. However, they could not comment on other label manufacturer's products and were aware of the reported problem. I tend to use blank CD-R which have a silk screen painted layer on the entire top surface. If using a label on these, it may provide an extra protective layer between the sensitive data layer and the paper label. I don't know if you are familiar with the construction of recordable CDs ? The really durable part, believe it or not, is the Lower surface, since this is quite a thick piece of clear plastic, which makes up about 90% of the total thickness of the CD. The recordable dye layer, backed with a very thin silver layer, is actually on the Top surface and is very vulnerable to damage - much more so than the lower surface. I examined a CD-R, (which recorded badly and was just a 'coaster') by breaking it in two, and peeling the layers apart. As I said before, most of the thickness is just a clear plastic disc. The actual 'business' part on the Top layer, is VERY thin and has virtually no protection ! Having said that, scratches on the relatively soft lower surface, through which the laser reads the data in the dye layer, can attenuate, diffract or deflect the laser beam, resulting in faulty reading of the data. In the past, when I have had problems of this nature, I have managed to restore both commercially produced music CDs and CD-Rs to fully readable condition, using Metal Polish, to gently 'Buff out' the scratches. This only works with fairly light surface scratches, not deep damage and since the CD is already a bit of a lost cause, you have nothing to lose in trying to restore it! Incidentally, this 'Label Adhesive' problem does not apply to commercially manufactured CDs, since they are produced by a totally different process. Another point about labels, of which I am sure you are aware - it is very important that they are placed centrally on the CD, using a suitable tool. Any eccentricity between the CD-R and the label can cause quite severe vibration due to the high rotation speed in the drive. This can result in faulty reading of the data. This is even more important on recordable DVD, since they spin at even higher speeds. There have been reports about recordable DVDs being unplayable when labels have been applied, even when they were apparently fitted centrally. This was thought to be due to differing densities in the paper label causing uneven weight distribution across the DVD and therefore setting up vibration when it was spinning. Because the optical track widths on DVDs are much smaller than CDs, it does not take much in the way of eccentricity to cause bad reading. And of course, once these labels are fitted, you can't get 'em Off !!!! The comments about chemical reaction probably applies equally to Recordable DVD. I Hope the above may been of some use.
------------------ Willum
_________________________
Willum
After silence, that which comes nearest to expressing the inexpressible is Music. Aldous Huxley ( especially when the music is played on a KN7000....)
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