Black rhodium or Oxidizing?

I am trying to get that look that a lot of indian jewelry has and
some big designers like JAR utilize in their designs. basically the
top parts of the gold are high polished white gold and the crevices
and underneath areas of a diamond are black. below are two links of
examples. i know there is the antique paint but im guessing this
isnt the most perminent solution. is this done using black rhodium or
maybe oxidizing gold? my pieces are made of gold and not silver.

thanks so much