Of the platinum group of metals -- platinum, palladium, iridium, rhodium, osmium and ruthenium -- palladium has the lowest specific gravity and the lowest melting point. William Hyde Wollaston and Smithson Tennant isolated palladium as a separate member of the platinum group in 1802. It wasn't used in jewelry until 1939, when platinum was declared a strategic metal and reserved for military use.



However, Palladium use was not restricted and was soon promoted in the jewelry trade press as a viable alternative to platinum. Because it weighed less than platinum, palladium jewelry could be made larger and still be comfortable to wear. In addition, palladium's malleability made stone setting a breeze. Palladium also could be combined with gold to produce a version of white gold, another substitute for platinum.

Despite these advantages, palladium was gradually phased out after World War II when platinum became available again. Palladium does have its drawbacks.

It's the only member of the platinum group that oxidizes when heated. This bluish purple oxidation is easily removed by quenching the piece in water. Repeated heating and quenching can cause the metal to become brittle and crack.

Platinum is impervious to all acids except aqua regia. Palladium is solvent in aqua regia, attacked by nitric acid and sensitive to sulfuric and hydrochloric acids. Palladium's color may be a pleasing light gray, but it doesn't take a high polish. It also has a tendency to become dull over time. These disadvantages outweigh palladium's lightweight malleability.

Many jewelers refused to work with it once platinum was again available. Most of the palladium jewelry made during the mid-20th century in the U.S. isn't visible in today's estate jewelry market.

One thing to consider is that jewelry fabricated in the U.S. is not always marked to indicate metal content and fineness. This opens up the possibility that some palladium jewelry is unknowingly being sold as platinum. Reports indicate that a number of palladium pieces were rhodium-plated to give them a better color and a few pieces were goldplated in the 1970s, when yellow gold set with diamonds became fashionable for daytime wear.

Because it's tricky to work with, particularly when repairs are needed, there isn't much of a demand for palladium jewelry among estate jewelry dealers. A large amount of palladium jewelry from the 1940s and 1950s was dismantled and sent to refineries. The price for palladium fell to around $280 an ounce in the 1980s, resulting in a flutter of palladium activity among craft jewelers, but it was short lived.

Despite this general rejection, palladium continued to be used in the 1950s through the late 1990s, especially as heads or plates and strips for bead-setting diamonds.

Researchers recently discovered palladium performs better than platinum in catalytic converters for combustion engines and in oil refining and industrial demands have vaulted palladium's price to $700 an ounce, making it impractical for jewelry use.

So, palladium, a metal which was once seen as a platinum jewelry substitute, has found a new role as an important industrial material.