A photo restorer walks through the process of restoring a tintype photograph from the 1870s.
My standard operating procedure is to use an ultra-high resolution camera combined with a top-of-the-line macro lens to photograph tintypes. I use strobe lights to illuminate the artwork. Strobes produce "hard" light, much like the sun on a clear day. In addition to the strobes, I place a polarizer over the camera lens and polarizer gels over the strobe lights. This eliminates all reflections and enables the camera to pick up a greater tonal range along with more detail.
The original photo is on the left and an intermediate step on the right; you'll need to click through to see the finished product.
Update: This is a better restoration...the one above is too airbrushed, like the photo on the cover of a fashion magazine.