I’ve been trying to figure out a setup that would allow me to take pictures of the backs of video game discs that would show any scuffs or scratches the discs have. I’ve tried a lot of variations but haven’t managed to get a good shot.
IMO, it works best with the camera at a low angle up close to the disc, and try a single light source in different directions. Nothing fancy: a normal lamp usually works for whatever I'm doing. The trick is finding the right angle for the specific situation, especially for highly reflective surfaces. Macro/close up mode also helps.
For highly specular surfaces with scratches on, setting up a scene where the direct reflection off the specular surface is as dark as possible, then lighting the surface such that the scratches are highlighted by the light source should be key here.
The trick will be finding a light source direction, and size of light source that highlights the scratches without also highlighting the pits and lands that make up the data on the CD. This will vary depending on the process used to make the CD, and its manufacture, writable versus read only disks will give drastically deferent results.
So for example placing a large piece of black fabric so that its image reflects off the surface of the CD into the lens; then side lighting the CD should likely do the job.
If the scratches all have a common orientation, placing the light source perpendicular to it may be helpful.
Lighting that is almost parallel to the surface of the object will emphasize texture (scratches, whatever). Shooting straight on - i.e. mostly perpendicular to the light source - with a large enough depth of field (shouldn't be too difficult if the surface is mostly flat) will show that texture the best.
You have a couple of choices. The terms are "Dark line" and "Light/or White line" lighting for glassware.
Against a dark background scratches and dust will look light and vice-versa against a white background. The lighting set-up to use would duplicate the same set-up you use to see the defects.
In other words, if you can see the defect under directional lighting with a reflection of a dark background you'd put the lens where your eye was and thus get the wanted view.
Conversely, if against a light/or white background is better you'd do that. I found that depending on the surface either might work. My disks were black and showed no artifacts with either set-up clearly, however, silver ones were easy.
Find an evenly illuminated diffuse light as your source and "play" with the best angle that works for you.
I found that 45° lighting to the surfaces worked well with the CD that I just trashed to find out.
Good luck. (Handle your disks by the edges unless you also want a record of your fingerprints.)