White gold jewelry is a hot fashion trend that doesn’t show signs of cooling off any time soon. Manufacturers are producing it, retailers are buying it, and consumers are demanding it, but none have a clear definition of what alloys can truly be called “white” — until now. A White Gold Task Force led by MJSA and the World Gold Council, comprising members of the supply, manufacturing, and retail components of the jewelry industry, has established a definition of white gold.
After measuring more than 70 samples of 10k, 14k, and 18k white gold jewelry using the CIELab and ASTM Yellowness Index, the Task Force defined “white gold” as a karat gold with a Yellowness Index value of 32 or less. It also proposed a three-tiered grading system in which to categorize white gold as Grade 1, Grade 2, and Grade 3.
The purpose of this grading system is to standardize the language used between suppliers, manufacturers, and retailers when ordering white gold, and to establish a quality system by which white gold is measured. This article addresses manufacturers’ issues as they pertain to working within the framework of this new white gold standard, and the benefits and pitfalls of using specific alloys. It begins with a look at the issues related to a common white gold alloy, nickel.
|Photo by Gary Dawson|
While the EU Nickel Directive, which dictates a maximum rate of release of nickel from jewelry onto a wearer’s skin, is primarily aimed at manufacturers selling white gold products in Europe, the concept of going nickel-free is something that jewelry companies may want to consider regardless. The Directive was prompted by occurrences of allergic reactions — namely nickel dermatitis in people who wear nickel-containing white gold. Studies done in the U.S. and abroad have shown that between 2 percent and 15 percent of people are susceptible to nickel allergies. Since this is a universal problem and not market-specific, chances are that most companies have customers who would like to buy and wear white gold but simply can’t. And unless the goods are marked “nickel-free” or “non-allergenic,” the customer may not be aware of any problem.
Regardless of whether a company needs to meet the EU Directive guidelines or simply chooses to in order to enhance its customer base, it’s possible, although admittedly difficult, to comply without going completely nickel-free. What is important to remember is that what matters is not the degree of nickel content, but its release rate onto the skin. Some nickel-bearing whites, depending on how they are processed, have a lower release rate than others.
Dr. Christopher Corti, consultant to the World Gold Council, notes that to ensure your metal will comply with the Directive’s standards, nickel content must be tested for in a manufactured state as opposed to raw alloys. He points to a study published in Gold Technology, issue 29 (2000), which notes that “one cannot just do nickel-release tests on the basic semi-fabricated alloys… The alloy may pass the release test in this condition, but the same alloy, when fabricated into jewellery, may fail the test.” Processes that change the metal’s metallurgical state, such as annealing, casting, or working, can affect the release rate.
Corti suggests that, for accuracy, all testing (preferably on finished products) should be done by an outside lab with facilities for conducting nickel-release tests. Stateside, he recommends the American Assay and Gemological Office in New York City; foreign companies can have testing done at the Birmingham and Sheffield Assay Offices in the UK, or FEM in Germany, for example.
Rhodium Plating and Wear
Some whites just aren’t white enough. For example, any white gold that falls in the Grade 3 range on the Whiteness Index should be rhodium plated; those that fall into the Grade 2 range are rhodium-plating optional. Rhodium plating provides a bright white finish, but it wears off over time, especially if it’s not done properly. And “properly” means getting the right thickness.
Common practice has jewelers dipping pieces in the plating bath for about 15 seconds. This leaves a very thin deposit that will readily wear. In a study conducted in 2003 by Red Sky Plating Corp. in Albuquerque, New Mexico, company president Neil Bell suggested that 1 to 3 minutes, depending on the temperature of the plating solution, is optimum for imparting a bright, lasting finish. (Complete results of this study were previously published in the May 2003 issue of AJM.)
Several factors must be in place for a lasting coating of rhodium. First, the piece to be plated must be very clean. Poor cleaning can result in insufficient adhesion of the rhodium or discoloration and streaking. Jewelry to be plated should be cleaned first in an ultrasonic to remove any dirt or polishing compound. Next it must be “activated” by immersing it in a heated bath, known as an electrocleaner, at about 150°F/65°C. This is followed by an acid dip, typically 10 percent sulfuric acid to 90 percent water, for one minute. Finally, the piece should be rinsed with distilled or deionized water.
After cleaning, the piece should be checked for “water break.” All water on the surface of the piece should coat it evenly. Spots where it breaks away have not been properly cleaned and activated. If water breaks occur, cleaning must start all over again.
In Bell ‘s study, a 1 inch square of 14k with a hole in one corner was used to determine the most effective solution, voltage, and bath duration for plating. Tests were conducted at two different temperatures — 115°F/46°C and 90°F/32°C — at times ranging from 15 seconds to 5 minutes. At 115°F, 1 minute in the bath created the best color and deposited a plating of 4.4 to 8.2 microinches on the metal. At 90°F, bright colors were evidenced in baths from 30 seconds up to 3 minutes, with thicknesses ranging from 1.9 microinches at 15 seconds to 15.6 microinches at 5 minutes. At the 1-minute mark, however, the results of the 90°F bath were similar to those of the 115°F bath, depositing 4.4 microinches to 7.9 microinches. Longer times in the 90°F bath resulted in hazy surfaces; the same occurred in the 115°F bath at both shorter and longer times.
While it’s likely a “your mileage may vary” situation must be tailored to the time your company wants to spend plating, the results are clear: for the best rhodium plating, keep it clean and let it bathe. If you’d prefer to forego the rhodium plating process — and the potential for wear — all together, it’s advisable to choose a Grade 1 alloy.
Casting Nickel White Gold
Anyone who’s tried to cast nickel white gold will tell you that you’ve got to watch for cracking. Stewart Grice, mill products director for Hoover & Strong Inc. in Richmond, Virginia, notes that below roughly 1,472°F/800°C, white golds tend to separate into two phases: one is nickel- rich, the other is gold-rich, and neither is especially compatible with the other. If it’s not handled properly at this stage, it can become susceptible to fire cracking or hard to the point where it’s difficult to work.
Timing in quenching the metal is key to avoiding this — but it’s going to take some trial and error. “We recommend waiting until the material has gone past what we call ‘black heat,'” Grice says. “When the top of the button has lost its iridescent red color, it’s in black heat. It then becomes safer to quench it. But this is no guarantee that it won’t crack.” Keeping track of cooling times, temperatures, and other job-specific data will help in repeating good results. “If in doubt,” Grice adds, “don’t quench it.”
There can be a lot of “if in doubt” moments when it comes to casting, says Linus Drogs, president of Au Enterprises in Berkley, Michigan, noting that common wisdom holds there are 15 to 18 different variables that can affect a casting. “There’s no way to clearly define ‘this is how you do it’ for every particular material,” he says. “It’s all trial, error, and experience.
“The key to everything in casting is consistency,” he adds. “What you need to be able to do is repeat your procedures, day in and day out, from small things to big things. For example, we measure the water we use every day for pH level, temperature, and contaminants. Water quality variables differ from season to season.”
Keeping a close eye on those variables and doing what you can to control them can help maintain valuable consistency during casting.
Casting Palladium Whites
One piece of advice that Daniel Ballard, national sales manager for Precious Metals West in Los Angeles, has for jewelers looking to successfully cast palladium whites is this: Treat it like the platinum group metal it thinks it is.
“It brings a lot of platinum family attributes,” Ballard says. “It has a high viscosity, even at extreme casting temperatures. It has a real ability to absorb and do harsh things with hydrogen gas or to react to a carbon crucible and cause porosity.” The list, like platinum’s, goes on.
For the best results, make sure your casting methods meet these noble requirements. For example, palladium whites require much higher temperatures to cast — temperatures that many investments designed for other golds simply can’t handle. “Makers of most investments used every day for yellow gold casting will tell you not to burn out above 1,300°F/704°C to 1,500°F/816°C, depending on what brand we’re talking about,” Ballard says. “But all high-colored [palladium] whites run in excess of 2,000°F/1,093°C. You can imagine the havoc that [metal this hot] does to an investment that the maker tells you starts to break down at 1,400°/760°C. You can get a lunar landscape from the reaction between the very hot gold and the silicon-based investment.”
Ballard suggests checking carefully with your supplier to see if they carry investment made specifically for these high-temperature whites. “Some companies that specialize in investment may carry their own,” he adds. The good news is that with the increasing popularity of white golds, more investment makers are addressing the problem with new products.
Outside of choosing the right investment, careful control of casting temperatures is also imperative, says Drogs. For the best results, he suggests induction melting because it provides control over temperature and will maintain a neutral or reducing atmosphere during melting. For those who aren’t so equipped, the same watchfulness must apply — but you’ll have to rely on experience, instinct, and a keen eye.
Fabricating White Golds
If you’re going to be doing fabrication work with white gold, don’t take it swimming right after annealing. No, it won’t get cramps; it will just become brittle. “It’s got to do with the interaction between the copper, nickel, and gold as the metal freezes,” says Ballard. In other words, don’t quench white golds. Let them air cool, preferably on an iron plate.
With nickel whites, remember that the metal can separate out into two phases when heated, which can cause some difficulties in working. “They’ll want to deform at different rates,” Grice says. “If you put it through a set of rollers or a wire-drawing guide, the nickel-rich area will be a lot harder than the gold-rich area. The soft metal will move a lot more than the hard one and you’ll get fractures between those two phases.”
Those two phases will also have two different grain sizes that need to be made more uniform. “If you just give it light work, you’ll end up with a sort of internal stress mismatch called a stress gradient,” Grice says. This is what causes cracking during annealing. In order to avoid this, the material should be worked down to roughly 50 percent of its size prior to annealing.
Palladium whites avoid much of this, since gold and palladium get along much better than gold and nickel. One problem, however, is that they tend to be very soft and require a lot of working to harden (particularly gold/silver/palladium alloys), especially at higher karats. “When you get down to 14k, [it’s easier to] get a bit of hardening,” Grice says. For improved ductility, he suggests quenching palladium whites — although you may not need to. “They’re very forgiving,” he says.
Choosing the Right White
Selecting the proper white gold for your next design can be a very simple matter. In fact, the guiding principle behind it is applicable across the board in jewelry: Make sure the material fits the method.
“You need to have a picture of what your tooling and your processes are, and a handle on the demands of your particular product line,” says Ballard. “You don’t want to create a misfit.”
As an example, Ballard points to resistance electric melters. “Because of the high temperatures needed for palladium whites, resistance electric melters are often not up to the task of properly mixing the alloys or properly melting karated gold for casting,” he says. “A casting machine is like any mechanical device. It cruises along when it’s running at a fraction of its capacity and it strains at the limit. Resistance machines need to run at or above their limit to get white gold done correctly.”
With the restrictions on nickel and the price of palladium, some white gold manufacturers are finding potential answers in the new manganese whites. “They have some interesting properties compared to other white golds,” Ballard says. “They flow at remarkably low temperatures — in the 1,500°F/816°C to 1,600°F/871°C range in 14k and 18k. They fill small voids like nothing else I’ve ever seen cast — at least as well as 10k or 14k yellow.”
On the downside, he adds, manganese whites react quickly and harshly to oxygen, so they must be cast in a neutral or reducing atmosphere. When torch casting, hydrogen is the gas of choice with these metals, he finds, since it strips oxygen out of the air immediately around the metal. In finished product, the colors of manganese whites rate as Grade 2 or Grade 3, so they are likely to require rhodium plating to get a satisfactory color. They also tarnish quickly when exposed to many household chemicals, so plating again becomes a necessity for prolonged product life.
“The biggest problem is that there is no perfect white gold alloy,” Drogs says. “Every alloy has been tailor-made for some specific purpose, whether it’s white-white or malleable or settable. And some of those properties affect other properties.” He points to the big push on rhodium-free white-whites. “There’s a downside to them,” he says. “Most ultra-white [nickel] golds are not setting-friendly. They’re going to be very hard.”
Again, it’s a matter of matching the metal to the job at hand. For example, if you are setting a fragile gemstone, such as an emerald, you may need to sacrifice the brightness of the white for an alloy that’s softer and more forgiving, or switch to a more expensive palladium white.
Metal choice is also dictated in large part by how rich a white color you need and whether or not you intend to plate. “The best color you can get from a nickel-free white is going to come from palladium,” Grice says. This, of course, means paying palladium prices. “In the lower karats, you can have it based on silver and zinc; they’re okay, but not what you’d call a good white color.” Other alloy combinations also provide varying grades of whiteness. What it comes down to is that in order to get strong color, you have two choices: plate it or pay for it.