The foil is where the data is stored. If there really is no foil in those spots, then there is no data to recover.
More specifically, the data is stored in microscopic pits in the back (foil side) of the disc. The foil allows the laser to reflect off that side of the disc so the reader can detect where the pits are. Without foil, the laser goes right through and it can’t tell where the pits are. If you google “CD foil repair” you’ll a bunch of pages that purport to give instructions on how to repair damaged discs, but most of them seem to be talking about fixing scratches on the read side (non foil side). I tend to doubt that it’s possible to repair places where the foil is actually damaged, since you’d need to reapply some kind of reflecting material that follows the contour of the pits, which are only a few hundred nanometers in size.
Sorry, the data exists in the poly-carbonate/dye layer. The reflective layer (not foil) is only about 70-80 nanometers thick, sputtered onto the surface in a high vacuum process, and serves to reflect the read (and write on recordable media) laser. The reflective layer makes the PC/dye layer visible to the read/write laser. The reflective layer is usually gold or silver alloy. Aluminum is usually used on standard CDs.
Darren Garrison is correct that the reflective layer makes the data visible. If that reflective layer is gone, there is no fixing the disc.
The dye/poly-carbonate layer is covered with a layer of UV-curable lacquer or resin on the label side, and is only 70 microns or so thick.
That’s why it’s important to be careful with the label side of a CD and especially CD-R. It’s VERY thin.
All of the above applies to CD media. DVD media is somewhat different.
Not pits and lands as on a normal CD. For recordable media, it’s some form of a “wobble groove” that’s pre-molded into the polycarbonate.
Your own terrible cite even says that’s not the case.
Just because you found a picture of a person picking the top of a CD off doesn’t mean that’s where the data is. As stated in this thread as well as in your link and even in a page linked on that page, it’s set into the CD further.
(Upon reading what I said earlier, I was incorrect to say the foil is embedded in the cd, I should have said the data).
Depending on how many minutes of audio are on the disk, the data may not extend all the way to the perimeter. If you look at the read-side of a few pre-recorded disks you’ll see an obvious difference in the visual “texture” of the inner portion that’s got data and the outer 1/2" or 1/8" that does not.
Big-label commercial CDs are usually packed to have nearly the full capacity of music. Customers feel cheated if they don’t get 65+ minutes of product from e.g. Sony Records. Small-label or local garage band CDs are much more variable.
If you find an outer region that has no foil backing and also has any non-transparent optical “texture” in the plastic you’ve got an unrecoverable mess out there.
If the foil backing does end well inside the disc’s physical radius, then any recoverable data is even farther inside that radius. So focus any cleaning or scratch restoration there. I’ve never heard of a successful way to repair any significant gaps in the foil backing. A couple-millimeter nick you might get lucky and restore enough bits for the ECC to correctly recreate the rest. A centimeter? Fuggedabouddid.
I’ve been working with CD-Rs since the mid-1990s, when I paid $500 for my first 2x burner and $12 per blank disc. I’ve burned literally thousands of them. I know what the hell I’m talking about. It does NOT FUCKING MATTER that the die is sprayed onto the plastic disc before the foil is laid down instead of on the foil before it is put on the CD–the fact remains that the foil layer on the top of a CD is profoundly fragile, and any chip or scratch to that foil sitting on top of the disc is death to the data underneath.
We’ve all been burning CDs since the mid 90’s. That doesn’t make you right. It didn’t make you right when you said the data was in the foil that would come off with water, it didn’t make you right when you showed me a cite of someone picking the foil off and it doesn’t make you right now…you’re still wrong by saying that the die [sic] is sprayed onto the plastic disc before the foil is laid down.
IOW, you’re missing the point. This isn’t about whether the dye is sprayed on the foil or the disc and sandwiched between them. It’s about the fact that it’s there’s a another layer of material between the data and whatever is on top. You can dispute that 'til you’re blue in the face, but you’ll still be wrong.
It’s embedded in the plastic. Virtually every website will show you that after making the disc, they spray on the dye, then add a layer of lacquer…then the top layer of foil as a bit of additional protection.
Having burned ‘literally thousands’ of cds doesn’t make you any more of an expert than someone who’s driven literally thousands of miles claiming to be a car expert.
Unless by ‘working with’, you mean you’ve been in the optical storage field or doing something besides burning cds. But in that case, I’d hope for a cite better than familyoralhistory . com, because I got mine from what appeared to be fairly serious information storage websites (clir.org and osta.org)
To be clear, it doesn’t look like the foil is worn or abraded off of the edge. Rather, the printed-on text isn’t actually printed, as in extra pigment, but rather, the letters show up by virtue of being transparent.
Sorry. The dye is spun (not sprayed) onto the bare polycarbonate, then the reflective layer is applied. After that, the protective lacquer is spun on and UV cured. Then the printed layer is applied via UV-curable ink silk-screening (usually).
I’ve never seen a CD-R with intentional transparent spots. Do you really mean transparent transparent? As in as transparent as in this photo of a disc that is delaminating? (Feel free to ignore Joey P if he tries to shit on that fact, too.)
(ETA I have seen blanks that have the letters in reverse–printing everywhere except where the letters are, but they still have the data layer beneath. Is that what you mean, or really “clear as glass” transparent?)
OK, I double-checked. Clearer than the majority of the area, but you’re right, less clear than the center clear part without any data.
The original recordable CD’s I used had a thick white layer of gunk on the data side. Presumably spun on. What technology was that?
Okay, that’s done on most of the top brands you’ll see in this Google image search. The presence or absence of that top printing doesn’t effect the readability. The cheapest bulk discs don’t even have top printing at all. (Several rows down in the search you’ll see a 100 disc spindle of unprinted discs.)
What timeline are you talking about here? The earliest ones I remember from the mid-1990s I bought at Office Depot. They were gold (I think most of them were gold in the beginning) and had minimal printing on the top. (And were 650 MB, came two to a pack in jewel cases and cost about $25 for the pair.) If you are thinking of later than the mid-1990s, then it might just be a surface meant to be writable. If you mean earlier, I never saw what the earliest ($20.0000 burner, $40 blank) looked like.