What’s All the Fuss? 

The use of palladium for fine jewelry is exciting considerable interest in the trade, with demand poised to grow. The high price of platinum (hovering around $1,020 per ounce at presstime) is one reason behind the new interest in this platinum group metal. Palladium sells for less than a third of that, typically below $300 per ounce, and therefore offers attractive profit margins.

It helps that consumers like palladium when they see it and learn its price. It has cachet both as a member of the platinum family and as a pure metal. Typically, palladium jewelry products are marketed as 95 percent pure and look similar to platinum. Unlike many white gold alloys, palladium does not require plating to achieve an icy white color. Which means its white sheen will never wear off, eliminating the bother and expense of re-plating faded white gold products to maintain customer satisfaction. Two factors in particular have energized the trade’s perception of palladium’s potential. First, palladium is about half the density of platinum (12 g/cm3 vs. 21 g/cm3), so more jewelry can be made from palladium per dollar invested in the metal. Moreover, U.S. stamping laws place no restrictions on marketing palladium jewelry products in the U.S. In many European countries, such as the U.K., palladium is not recognized as a jewelry metal and cannot be hallmarked.

So what do jewelry manufacturers need to know to work successfully with palladium? On the following pages, industry experts share their insights and experience from early trials with this new jewelry metal.

Alloys Like platinum 950 grade jewelry, which is now the standard in the U.S., palladium is also marketed at 950 grade, or 95 percent purity. As with pure gold and platinum, palladium is a very ductile metal. In its pure state, the metal’s hardness falls between 40 and 44 Vickers annealed or as-cast—not hard enough to be practical for jewelry production. That’s why metal suppliers are scrambling to develop alloy compositions that they think will provide the optimal balance of purity, hardness, and workability. Current 950 alloys are based on palladium-ruthenium with other additions, such as silver and gallium. (See “Palladium Alloys,” page 37, for a list of jewelry-specific alloys.)

Casting Castings made of palladium are susceptible to the same problems that plague all cast metal—crack propagation, porosity, and undesirable surfaces. Many of these defects are caused by common reasons: lack of experience with a given metal, improper equipment, and the absence of effective controls to ensure quality and process repeatability.

Pure palladium melts at 2,826°F/1,552°C, and current 950 grade alloys have slightly lower melting ranges. This melt point is significantly higher than karat golds and approaches those of platinum alloys. Thus, investment casting requires higher temperatures, underscoring the need to pay attention to the temperature capability of the casting equipment selected for processing palladium. “Investment casters who are experienced with platinum already have the basic production resources necessary to work with palladium,” says Stewart Grice, mill and refining director for Hoover & Strong Inc. (www.hooverandstrong.com) in Richmond, Virginia. “The high temperature requirements of platinum create a production environment that can easily service the lower temperature requirements of palladium.” Still, knowledge about—and experience with—palladium go a long way.

Although palladium is part of the platinum family of metals, it’s risky to think you can apply your platinum experience to palladium challenges without spending time on the learning curve. This is true whether you melt using a torch or an induction furnace. One important difference is that palladium, unlike platinum, requires a special atmosphere or a vacuum to produce high quality castings. Palladium has a healthy appetite for hydrogen, a leading cause of alloy embrittlement. In addition to absorbing hydrogen, palladium can oxidize during casting. For these reasons, palladium should be melted or annealed in a hydrogen-free, non-oxidizing atmosphere. Control of the casting process is critical to success with this metal, according to  Teresa Frye, president of TechForm Advanced Casting (www.techformcasting.com) in Portland, Oregon. “The key to success is, first, an alloy with the right casting characteristics and hardness,” she says. Frye recommends the alloy have a hardness of greater than 110 Vickers so that the work piece is malleable enough to permit stone setting, but hard enough to be wear resistant.

 “The second key to success is a highly controlled casting process, particularly with respect to temperature and atmosphere,” she continues. “Techform has high volume production equipment with good process controls. I’d be hesitant to recommend casting at a bench with a torch because of the difficulty of achieving consistent output.” J. Tyler Teague, president of JETT Research (www.jettresearch.com) in Johnson City, Tennessee, also recognizes that both high volume manufacturers and small-shop jewelers will face challenges when they begin casting palladium. However, he says, “While it is far from ideal to cast with a torch, it is possible for a skilled artisan to produce attractive palladium jewelry working with a torch at a bench. I recommend using a propane and oxygen mix with palladium, rather than the mix of hydrogen and oxygen more commonly used with platinum. Properly adjusted, the flame of the torch can burn off the oxygen and reduce oxidation.” Hydrogen torches are not recommended.

Teague adds that if you are melting in an induction furnace, there are other factors to consider. “The melting point of palladium casting alloys is around 2,552°F/1,400°C; the melting point of platinum casting alloys is around 3,092°F/1,700°C,” he explains. “If you are using equipment that has been designed for the platinum casting process but do not have a way to reduce the power setting, you run the risk of overheating and thus contaminating the metal with silicon from the crucible. As a result, your alloy will become brittle and your castings will fall apart later.” Teague’s solution: Make sure the machine you use has adjustable power settings so you can precisely control the melt. Use a lower power setting than you typically use for platinum. It is also necessary to apply a zirconium oxide barrier coating to the crucible to prevent contamination of the melt. (Teague notes that you should never use graphite crucibles when casting palladium, as the carbon will diffuse into the palladium and embrittle it.) Under reducing conditions at high temperatures, palladium behaves like platinum and can reduce many oxides, such as silica, magnesia, and alumina.

However, palladium does not behave exactly like platinum when casting. With a density of 21 g/cm3, platinum can damage the investment mold as it enters the cavity and solidifies quickly. For this reason, platinum is typically cast in small lots. It is spun into small molds to avoid the damage that could be created by a high volume of such a dense material entering large molds. In contrast, the density of palladium is 12 g/cm3, almost half that of platinum. This property has positive implications for the design of the casting process. “The spruing can be more direct,” says Teague. “You can also populate a tree pattern with many more pieces. An efficient palladium tree can look a lot more like a silver or gold tree than a platinum tree.”

There are also design considerations specific to palladium. “Given that gold, platinum, and palladium all have unique flow properties, a design that works well in one metal will not necessarily work well in another,” says Frye. “We found that very lightweight or filigree designs had a greater tendency to no-fill when compared to platinum, but that medium to heavy designs work well. We need more data to determine whether the no-fill is strictly due to metal flow characteristics or some other variable unique to the palladium casting process.”