Easy Fix for Scratched CDs

NotQuiteOnto writes "Ben Hayes (om3ga) has performed an experiment as to the best method to fix scratched CDs. He set himself the criteria that it can't take longer that 5 minutes and it has to be something in his house. The result isn't what you'd think ..." Luckily, he stopped before "peanut butter."

Comments

Workaholics!

[inviolet]

Wax? Pledge? Toothpaste? Buffing?

Y'all are a bunch of workaholics.

Just lightly wave a propane or butane torch over the scratches.

It works for all polycarbonates, including CDs, DVDs, helmet visors, motorcycle windshields, airplane windshields, cellphone screens.

The trick is to wave the flame over it so very very lightly and quickly, that the rough edges of the scratch briefly melt and flow.

Re:Even Better

[famebait]

I've also tried various filling-in materials: chapstick, polishing wax, etc. They all seem to work as long as you can get the excess off cleanly. But I'm not certian if they work for the reason we like to think. One experiment left the scratch very visible, but the CD still working better. That got me wondering. So I tried filling with a positively opaque crayon (wiping away excess), and that worked too. I figured it could be done even quicker if I could skip the cleaning up, so I tried with a black fine-line felt marker, simly drawing a thin line on top of the scratch, and guess what: it not only worked fine, it could handle much larger defects than nothig else had been able to fix (well, actually there was a barely audible artifact, but aleast it played).

It has to be sad: this was on music CDs, so you can lose quite a lot of bits without serious harm to the result (and even a slightly audible tick is something you can live with), so it's not a fir comparison to software. But it did make me wonder: do all those remedies really help the machine read more bits correctly by repairing the refrective plane, as it is tempting to believe? Or do they simply allow the built in error correction do its job, by blocking the area where the (clear but warped) surface of the sratch would otherwise make the laser lose its tracking?

Re:Even Better

[poliopteragriseoapte]

This is similar to how you fix scratches or defects on telescope or camera lenses. The problem in even a large scratch or defect is not the 1% of lens area that will be unable to gather light. Rather, it is the fact that light is scattered all around by the defect, lowering overall contrast. So what you do is paint the defect black. This way, you lose an insignificant amount of light, but the contrast of the image is unaffected.

Perhaps for CDs there is a similar phenomenon. I am not sure how the error correction in a CD works, I am not sure whether it has the problem of "identifying" errors - I thought it simply applied to the data stream a standard decoding transform based on distance to a correct codeword. So perhaps part of the benefit of painting the defect black is that it cuts down on reflections, so that you can read neighbouring areas of the CD better?