Well, this is a bit strange, but for the third time today... Photographing clear glass is a challenge. Clear glass doesn't really photograph at all. What you are actually photographing is the reflection in the glass. In order to capture that, you have to have something that is being reflected. If you are shooting clear glass on a white background, you would typically use a black panel to reflect off the edge to give the glass definition. If you are shooting clear glass on a black background(as you are), you would typically use white panels to either side to give the glass definition.
Just adding a few panels and using a larger light source would make a world of difference.