|Rhodium is a hard corrosion-resistant silvery-white element of the
platinum metal group, occurring free with other platinum metals in alluvial
deposits and in nickel ores. It is used as an alloying agent to harden
platinum and palladium. Symbol: Rh; atomic no.: 45; atomic wt.: 102.90;
valency: 1-6; relative density: 12.4; melting pt.: 1966°C; boiling
pt.: 3727°C (approx.).
It is usual to rhodium plate all white gold jewellery in the UK and some
platinum. Rhodium is very bright, hard, and highly reflective and when
applied by an electrochemical process to white gold it forms a hard white
highly reflective surface to the metal.
This is the polished white surface
which you associate with platinum jewellery. When the rhodium plating
wears through the colour of the actual alloy can be seen. This varies
from a yellowish grey to a plain grey. On some cheaper jewellery, particularly
9ct, one piece castings are made from a yellow alloy. The highlights
or head of a ring is later made white by 'stopping off' the yellow parts
with something akin to nail varnish and rhodium plating the rest. The
mask is then removed to leave the two colour item.