Part of what I do is to accurately reproduce antiques for auctions often times these drawings and sketches are behind glass making it difficult to photograph without reflections. Not only is the correct color important the art can not be distorted and must be photographed perpendicular to the film/sensor plane. The only way to prevent reflections is to shoot in a darkened studio with lighting carefully placed as to not reflect back into the camera. In this case the owner wanted the detail of the pencil handwriting in the upper left and lower right photographed separately and ledgibly. The solution is to position the lights so they light the subject but the light reflected off of the glass bounces off and away from the lens. By hanging the art on the wall and lighting from above with a large soft box the incident of reflection sends the reflected light to the non-reflective floor covered with black paper where most of the light is absorbed. Very little light is bounced into the studio leaving nothing to reflect.
Here are the finals after a small amount of contrast adjustment in Photoshop.