DVD repair and CD repair of scratches can be performed in a number of different ways. However, most of the scratch repair methods do not solve the DVD scratch or CD scratch problem.
Scratches on optical discs may occur on the top side of the disc (label side) or the base side of the disc. Top side scratches to CDs will likely damage the metal layer and this type of scratch damage cannot be repaired.
If you hold the CD up to the light and you see light shining through the disc where the scratch is, then you have metal layer damage. Top side scratches to DVDs will not damage the metal layer because the metal and data layers are sandwiched in the middle of the disc structure. For the metal layer to be damaged in a DVD, the DVD scratch would have to be very very deep and if this occurs, you usually have a cracked or broken disc. This page focuses on CD repair and DVD repair of scratches on the base side of these discs.
Scratches may or may not cause problems when you play your CDs and DVDs. Whether they do cause problems depends on the size of the scratch, the depth of the scratch, and whether the scratch is radial or circular. Scratches on the base of the disc do not necessarily cause problems on CDs and DVDs. Circular scratches are very problematic because this creates bad data in a sequence and the error correction system cannot deal with this situation well since it relies on adjacent data to fix the bad data. Radial scratches create more of a random distribution of errors and this is handled well by the error correction. Also, if scratches are small and not deep, DVD repair and CD scratch repair are likely not necessary because these small scratches will not affect the laser light path that reads the disc.
If CD or DVD scratches do affect the performance of the disc, then you need a remedy to make the discs playable once again without problems. There are basically three types of repair solutions: fillers, polishers, and sanders.
Fillers are liquid substances that are applied to the disc in order to fill the scratch or gouge. Products are available commercially and there are many homemade type remedies that have been suggested. The key principal is that the filler is supposed to have the same refractive index as the polycarbonate base so that the laser light is not affected by the scratch as it reads the disc or in other words the scratch behaves just like the rest of the disc base and is unnoticed. Fillers that have this property are difficult to find and fillers often flake out of the filled scratch and contaminate the drive as the disc spins at high speed in a heated environment. Overall, scratch fillers are not effective at all for DVD repair and CD repair of scratches and will do more harm than good.
Polishers for Scratch Repair
Polishers are liquid solutions sold commercially that are applied to the disc base to polish out the scratch. The goal is to smooth out the large problematic scratch. Usually what happens is that a lot of smaller scratches are formed and the larger scratch may or may not be remedied. Bottom line is that polishers may help remedy the scratch to some degree, but often this technique makes things worse. If you have no other option for DVD scratch repair or CD scratch repair, then CD or DVD polishers may be worth a try, keeping the above stated risks in mind.
Sanders for Scratch Repair
Sanders are pieces of equipment that have been specially designed for CD or DVD scratch repair. You often find these in stores that sell used CDs or DVDs. This is how these stores restore problem discs that they acquire and they also offer this sanding scratch repair of optical discs as a service with cost depending on the severity of the scratch. Basically, the polycarbonate plastic base is being sanded down to the level of the scratch. The whole base is sanded with fine sandpaper, not just the area of the scratch. After sanding the disc base is repolished so that it is crystal clear once again. This method of CD or DVD scratch repair may or may not work. The main problem is that the base is being thinned out and this affects how the laser light interacts with the disc when the disc is read. This method is the most expensive of the scratch repair techniques and may lead to more problems with your disc but is probably your best shot at restoring a disc that will not play because of scratches.
With any of these scratch DVD repair and scratch CD repair methods, use them only as a last resort, when you have a disc that is scratched and simply will not play in a number of different players or drives.