Rhodium is a chemical element that is a rare, hard transition metal that can be found in platinum ores. It is used in alloys and acts as a catalyst with platinum. It is one of the most expensive precious metals in the world. Rhodium is a durable metal that exhibits higher reflectance in visible light. It has both a higher melting point and lower density than platinum and can't be attacked by acids.
"Although several different electrolytic baths for rhodium plating have been proposed, the only baths to achieve commercial significance are (1) phosphate for very white reflective deposits; (2) sulfate for general jewelry and industrial deposits; and (3) mixed phosphate-sulfate for general decorative deposits (Metal Finishing p.249 - Vol.102 no. 4A)."