hi, yester day i made those diamonds, in blender, for the render i use YAFRAY. The diamond model is not a model i made by my self. C&C is varry welcome.
Nice.
Can you tell us what was your lightning setup. How many lamps and differents colors ?
Because i’m wondering how you can have those achromatic effects (depends on the color, red or blue …).
It is just a white spot, and a white phothon lamp. And there a full GI on with cache, but not phothons.
But the matrials got dispersion with 100 samples and power to 0.3 the IOR is set to 2.42 witch is the IOR for diamonds.
Its dispersion in Yafray material settings.
Im more interested of the photon lamp settings. Can you show them please? 
The phothon lamp settings are.
Energy 2.000
Phothons 1000000
Search 151
Depth 5
Blur 0.075
Caustics are a bit to bright (just a little), and the floor material could have a texture.
Precious work, you can, please to place .Blend for download?
And, render time ?
The blend file can you find here http://jonas.klit-reiff.dk/diamanter.blend
The render time is ca 55 minuts, on a 3 Ghz and 512 mb ram.
I try to put it on some texture on the ground, and set the energy to 1.500 og somthing.
Here is a litle update, is it ok with the background or do you think that i should make a somthing more then just a plane, and is it better with the caustics now? Som more C&C would be nice.
The realism of the ground doesn’t match the realism of the diamonds.
There are almost no shadows, maybe it is the reason why.
Personally, I think these diamonds would sit well on a red smooth piece of cloth (with some waves), like in expositions.
