Ronny,
Sorry for the long delay in replying. My PC went down and I was in major panic mode.
I wanted to comment on background color again. You mention using gray backgrounds when photographing black subjects. I still use a black background. I just posted a black on black photo on the fossil section of this site for your consideration. Maybe there was enough “non-black” on the specimen to make this possible. The set up for the photo is a single flash with a white fill card on the opposite side.