Thanks for checking it out; I appreciate any help.

I think it IS a problem with my install of P6; no-one else has complained so far.
From my end, it isn't just about textures- if I load the glasses on their own into an empty scene, they just render solid black. If I change the diffuse colour of, say, the frame or one of the arms to yellow, it stil renders solid black. It's only when I put something else- anything- into the scene that the changes have an effect.

To recreate my problem, load the glasses into an empty scene, and change the diffuse colour of the arms or frame to something other than black. If it renders okay, then it's just me. If not, it's a problem with the model.

If you're not having any problems, I assume that no-one else is either- or I'm sure I'd have had some comments by now- so it must be down to my install. I think I'll try a re-install to see if that fixes it, since I recently did a video-driver update that played havoc with P6 and some other 3D programs too. I did revert to my old video-driver which seemed to fix everything, but maybe it didn't fix P6- you never know, I suppose.

(By the way, I do know that the freebie glasses has a slight polygon-glitch just above the lenses which doesn't really show up if you're rendering them in a dark colour, but that's why I gave them away as a freebie- my new ones are much, much better, which is why I'd like to sell them, since I've put in over 24 hours on one pair!)