More examples here.
An Arnold render I did using a model courtesy of the incredible Fausto de Martini. Got to love unbiased rendering!
Tests by Jamie Portsmouth.
” Arnold 5.3 adds multiple scattering to its microfacet model for rough metals, which restores missing energy. Here are renders of 4 different metals (gold, copper, silver, and nickel) with roughness increasing from left to right, and multi-scatter on/off in successive rows. “