Turn OFF the Flash!
To illustrate this point, here are two pictures of a drawing of my shoe. The piece was lying on the floor, I was standing on a chair shooting down, and natural light was coming in windows to the top and either side of my drawing. Here are the shots with flash (top view)
and without (bottom view)
There are numerous reasons that a work of art's owner might require a photograph of the painting, drawing or object in question. Aside from having the ability to email one's entire address book a digital image of a cool new (expensive) etching, a visual record may also be required for homeowner insurance purposes.
LINK How to Photograph Paintings (More info see comment)