I can't take credit for the plex idea....we had the oportunity to briefly meet a couple of the Smithsonian staff photographers a few years back, and they showed us some neat shots they had done that way....it may be surprising to some people, but the Smithsonian is one of the few institutions I've ever come across that actually uses hotlights in their studio....our conservators would freak out & kill us if we did that here....heat is one thing, UV output is another.....those guys were using massive fresnel keglights....one thing in common that we did was to use this reflector material called "lightform" that delta used to carry....it's discontinued now, but they were pre cut sheets of cardboard with silver on one side and white on the other...with a magnetic clasp...you could fold them up into little triangles and adjust the angles easily...they came with about 20 different sizes on a sheet, and cost about 15 bucks...

They were huge scroungers just like us too....we have a full carpentry/exhibits shop here and just use alot of scrap materials in the studio...like the mirrors and gatorboard, acryllic rods and mounts, plex etc....one trick we do for small backgrounds is to take an unexposed sheet of matte RC paper and run it through our processor...voila!--a clean white background....you want black? Fog it and run it through the machine....they did something similar, but used an RA4 processor and c-prints.....

So, you just have to be sorta creative...I've used the glass idea for shooting coins and small buttons, arrowheads etc....I'll clamp a thick, clean & clear sheet of glass to a bogen superclamp, and suspend it over a copystand setup about a foot off a background of maybe black velevet or some other color.....you can then skim hardlights and cast shadows out of the shot pretty easily this way. Or light from beneath as well...this is another way to get a very clean white background, but the problems come in dealing with reflections off the glass (you have to mask the camera), or dust on the glass....so, it's really a pain to do in practice. Sometimes it's what you need to do, though.

I can recommend one great, but out of print book on this sort of thing: Alfred Blaker's, "Photography For Scientific Publication", another similar book might be the Cambridge Press's "Photography for Archaeology and Conservation". The Blaker book is the best.....good luck & have fun, maybe start digging around the junkyards for studio props as well.....