I once took an old Xbox game disc that was scratched up to hell and brought it to a local used game store. They put it in this big machine near the counter and once it was done it was looking like it just came out of the case brand new.
How do the machines do that?
In: 10
There’s a clear protective layer on the underside of CDs that serves to protect the pits and lands that make up the data on the disc. It doesn’t normally affect reading, because it’s optically clear, but when you scratch the bottom of a CD, you’re putting a scratch in that layer, which causes the laser in the reader to bounce incorrectly.
What a CD resurfacer machine does is eat away at the remainder of the layer, removing material until it’s all one depth again, restoring the ability of the drive to read the disc. Obviously, there’s only so many times you can do that, depending on how deeply you’ve scratched the disc.
The data is stored on the aluminized layer. This is considerably closer to the label side of the disk, than the side which is read. Scratches on the bottom will cause the plastic layer to no longer be normal to the laser beam. The scratch will cause the laser to bend and or disperse due to the air-plastic interface no longer being at the expected angle.
There are two ways to fix this.
1) Remove some of the plastic until you are below the depth of the scratch. Scratches are obvious on CD’s but most are not really deep. In this case, the machine would just polish the disk. You can use toothpaste as a polishing agent to remove many scratches on a CD. While you are taking off only a little bit of the clear plastic, you are removing some, so this can only be done so many times (depending upon the depth of the scratches).
2) You can add material that has the same refractive index as the plastic to fill the scratches. This is how they fix those small dings and chips in windshields.
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