What are the "Physical Differences" between CD-R and CD-RW?
Does anyone know the answer to this? Just recently I have bought a pack of CD-R's (Verbatim), up until now I have only ever bought CD-RW's, I could never see the point in WRITE ONCE discs. But I thought, I have some music I want to back-up and keep permanently. So I started to burn my first disc (CD-R). It crapped out. So I want to know whether it is worth buying anymore? A diagram if possible please.
Both media are identical in terms of their polycarbonate base. For a CD-R, there is a layer of photo-sensitive dye spin-coated on top of the base that is dried and cured before a vacuum chamber applies a very thin layer of silver alloy on top of the dye. Immediately after emerging from the chamber, a lacquer is spin-coated on top of the alloy layer. From that point on the disc is finished, but additional thin layers of silk-screening or ink-jet printable surfaces can be applied.
The base of a CD-RW goes into a 5- or 7-stage chamber vacuum where multiple layers of semi-metal alloy are vacuum deposited onto the disc. The last stage applies the silver alloy mirror layer. From that point on, the manufacturing is identical to a CD-R: spin-coated lacquer, silk-screen printing, and so forth.
Repaired? I'm assuming that it doesn't look like Superglue, nails, staples, or adhesive tape is in order. The chief culprit for damage to CD-Rs is debris on the bottom that blocks the laser. Cleaning sometimes improves the condition enough to get a drive to read a disc enough to transfer the data to another, cleaner disc. Use eye glass cleaner intended for polycarbonated lenses, and wipe radially--from the center hole outwards towards the edge. Wiping circularly, as if drying a dinner plate, increases the chances of scratching the disc in the circular path of the laser. A radial wipe would cause a scratch 90 degress across the path, thus limiting the damage in the path.
The second most common damage is a scratch to the bottom of the disc. There are some cleaner/polisher combinations that will smooth out a scratch enough to transfer data. Don't use the original disc again after transferring it. The next source of damage is to the upper surface, and nothing can help there because the recording surface is destroyed. I was once asked to repair a "poor quality" CD-R that didn't work. A cursory look at the bottom told the story: the user had misapplied an adhesive label, pulled it off, then reapplied the same label. A pie section of lacquer and alloy had been ripped from the disc and shifted 10 degrees, leaving a clear view of the bottom of the adhesive label from the bottom of the disc. There is no possible way to repair that kind of damage.
