Ira Tiffen, of the Tiffen filter company, has a general article on using filters here:
It includes a paragraph that is relevant to your interest:
"For relatively close imaging of documents, pictures, and small three-dimensional objects, in a lighting-controlled environment, as on a copy stand, large plastic Polarizers mounted on lights aimed at 45 degrees to the subject from both sides of the camera will maximize the glare-reducing efficiency of a polarizer on the camera lens. The camera, in this case, is aimed straight at the subject surface, not at an angle. The lighting Polarizers should both be in the same, perpendicular orientation to the one on the lens. Again, you can judge the effect through the polarizer."