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There is a common home-remedy for scratched flat-screen monitors that says to rub a bit of petroleum jelly into the scratch. The rationale being that because the jelly has a similar refractive index as the plastic of the screen, light does not refract when moving from the jelly to the plastic and back as it does when moving from air to the plastic and back.
This makes sense, and some people have reported successful results, but naturally it depends on the specific jelly and specific monitor. Others have reported less success which also makes sense because there is a wide variety of jellies and monitors.
In this vein, I am wondering about optical discs. Scratches are a common blight on CDs and DVDs that most people have had to deal with at some point. It stands to reason that a similar technique could be used with optical discs (at least once, to recover the data). Even better, there is not as much variety with discs; they all use standard polycarbonate with little variation in their chemical composition, so the same material should work for pretty much all discs.
Does anyone know of a material which has a refractive index as close as possible to that of polycarbonate (1.584-1.586)?
There’s two things to note:
The disc spins very fast in the drive, so it can’t be something too soft because then the particles could get spun out and splattered inside the drive.
CD/DVD repair-kits often include some sort of chemical solution, but a home-remedy should be a substance that most people can easily and cheaply get a hold of.
Synetech
Posted 2013-12-16T17:47:09.857
Reputation: 63 242
1I would imagine "good enough" for our eyes is not "good enough" for a laser. The DVD repair kits are more about buffing the scratches out and returning the plastic to a smooth surface. Whatever you fill the scratches with has to actually have a flat surface and not concave inward or bulge outward from the scratch. – Darth Android – 2013-12-16T18:02:17.863
True, but if it has the same refractive index, then the laser light should not refract when it changes mediums. Of course this is on a microscopic scale (or more accurately nanoscopic scale), so it would have to be very similar since even a little deviation would be a problem.
:-/– Synetech – 2013-12-16T18:04:22.310@Synetech It won't change angles when going between filler and plastic, no, but unless the plastic is the same refractive index as air, the laser will refract when it goes from Air<->(plastic/filler), and the point at which it refracts must be the same, which means you must have a perfectly smooth surface on the filler material, which is also perfectly level with the surface of the plastic from one side of the scratch to the other, and that's where I think you'll run into problems. – Darth Android – 2013-12-16T18:27:18.723
That’s a good point. Of course if it had to be perfectly smooth, then you would have problems with even minor scratches. Fortunately, optical media has a lot of error-correction built into the design which helps to deal with that exact issue. – Synetech – 2013-12-16T18:37:10.720
Yes, there are some how to fixed scratched disc questions, but none of those address this particular question. Those always end up saying to use toothpaste or a repair kit or something. The closest I could find to this question was a post that suggested using “Vaseline, liquid car wax, neutral shoe polish, or furniture wax”. That’s a lot guessing at random substances which are very different from each other. If guessing is enough, then I can do that too: try super-glue or canola oil or tomato paste or mercury or leather.
:-/– Synetech – 2013-12-16T18:40:56.937You fix scratches in disks by buffing them down (toothpaste, for example), not by filling them, for the exact reasons Darth Android pointed out in this comments. Anyhow, if you are looking for a chemical match to a specific substance, then SU isn't the place to ask (as that has nothing specific to do with computers. Maybe check http://chemistry.stackexchange.com/). If you're looking to repair a scratch disk, then that was already asked and answered (see suggested dupe). As-is, this seems more like an XY problem.
– Ƭᴇcʜιᴇ007 – 2013-12-16T19:15:56.380You fix scratches in disks by buffing them downMore accurately, you can fix them like that; that’s not the only way.not by filling themWhy not? One time I accidentally solved it exactly in this manner. I rubbed a scratched disc with an oily napkin and suddenly it worked perfectly (I just wish I knew/could remember what kind of oil it was).For the exact reasons Darth Android pointed out in this comments.To which I gave a valid rebuttal. – Synetech – 2013-12-16T19:38:43.457belongs on diy.stackexchange.com – kinokijuf – 2013-12-17T19:07:45.547