Use Indigo.

http://www.indigorenderer.com

I export my MoI (.obj, ngons, medium complexity) into Blender, then use Blendigo to assign materials.

Using an unbiased MLT renderer like Indigo (or Maxwell, or Fryrender, etc) means no wierd lighting set up or modes or anything - just set up some light boxes and a backdrop, just like a real studio set up, and then render. I'm surprised Jewelers are screwing around with material settings and stuff for their renders.. - pick a .nk file (or .ior, in maxwell's case) as the material, and you get perfect gold, copper, aluminum, etc.

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Example image:
http://zsouthboy.com//displayimage.php?pos=-176

If you guys want a step by step tutorial, I'll write something up for this forum.