That's probably just about the worst way you could shoot glass. The key to glass is to have your background just big enough to fill the frame, and then around the edges of it, have a different color to reflect in the edges of the glass, giving it some edge definition. For instance, if you're using a white background, put a bigger black background behind it, and make the white background as small as you can get away with. If you stick it in a lightbox, it'll have zero edge definition, pretty much ruining the shot. Those things are not the all-purpose solutions that everyone wants them to be...