After a long search

I finally (& inadvertently) find a backdrop that makes the chalcedony beads just pop!

Great colour & wonderful light absorption resulting in crystal clear eadges on the bead with no pesky reflection.

Of course the downside is that it sheds, is tempramental, knocks things over & moves right when you have everything set up & about to depress that shutter button.

I guess the search is still on ....