Trouble using black backdrop

I need help (again!!) I know I'm doing something wrong.

Last night I was trying to get some close-ups of a piece of glass sculpture (a large
4'' marble) and wanted a black background.

I used a black bed sheet and shread it out on my bed. I then placed the marble
in the center.
I had 2 photofloods w/ fixture and reflector, one on each side and raised about
4 feet.
Trouble is, the black sheet actually reflects just enough light to turn the black
sheet dark grey and nasty looking.
How do I get a nice jet black background? I cant distance the marble from the
backdrop so the lights wont hit it, so what do I do?

I take it you are shooting the sculpture straight on, not from the top down? If so you might want to try putting something to block the light from hitting the background like I've shown in my award winning drawing.

The blue lines represent where you can put the stuff used to block the light from hitting the background.

I don't have any lighting tips for you, but I do have a background tip. Get a yard or two of black velvet. Velvet really soaks up the light! Here are a couple examples of things I shot using black velvet as my backdrop.

http://gallery.photographyreview.com...0/IMG_0679.jpg

http://gallery.photographyreview.com...0/IMG_5716.jpg

Thanks for the detailed post.
Sounds like I have to figure out how to put some distance between my subject
and the backdrop.
I do not want to put the piece on a stand or table, I want it free and disconnected.

I will try to post a pic tomorrow to show you what I mean.
I have already taken the pics, I just haven't downloaded them.