De-oxidized Sterling Silver Alloys

Sterling silver alloys typically contain about 7.5 percent copper, an addition that not only provides strength to the otherwise pure silver, but also helps the alloys to tarnish fairly quickly—a traditional frustration for jewelers and consumers alike. In addition, both copper and silver readily absorb oxygen when in a liquid state, leading to issues with firestain and gas porosity that has confounded many a caster.

In recent years, metallurgists have discovered that replacing some of the copper content with deoxidizing elements, such as zinc and silicon (in casting alloys) and germanium (in alloys geared toward fabrication), increases the resistance to both firestain and tarnish. This has led to the creation of several proprietary de-ox alloys now on the market. They all resist tarnish and offer a whiter, brighter look than found with traditional sterling. In addition, several help to protect against firestain and can be easily fused (thus avoiding solder).

Sounds great, right? But swapping out some of that copper for other materials means that these alloys don't always behave in the same way that traditional sterling does. To help you get to better know these alternative silver alloys, we've asked jewelers and metallurgists to explain how these alloys are different, and why they may warrant a place in your shop.

Getting to know you

When many jewelers think of deoxidized silvers, the first thing that comes to mind is the tarnish resistance they offer. Metallurgists are quick to point out, however, that tarnish resistant is not the same as "anti-tarnish" or "tarnish-proof."

"All de-ox sterling silvers will eventually tarnish," says Dr. Shan Aithal, corporate metallurgist at Stuller Inc. in Lafayette, Louisiana. "It's just a matter of how slowly."

Among all the noble metals, silver is chemically the most reactive and readily combines with sulfur and chlorine, main elements that cause tarnish in traditional sterling silver. The addition of copper in these alloys further decreases the tarnish resistance by  adding oxygen to this list. When the silver and copper in the alloy react with sulfur in the atmosphere, silver and copper sulfides are created at the surface of the metal.

Adding de-ox elements to a sterling silver alloy not only reduces the amount of copper in the alloy, but can create "a passive oxide surface to prevent or at least reduce the penetration of oxygen into the alloy, so less copper oxide is the result, "says James Binnion of James Binnion Metal Arts in Bellingham, Washington.

The protective oxide layer is a reason why many bench jewelers initially turn to these de-ox alloys. Ruthie Cohen, a jeweler, educator, and the owner of Timeless Jewelry Designs in Arden, North Carolina, likes to create her silver pieces using Stuller's Sterlium Plus de-ox alloy primarily because of its tarnish resistance. She says that finishing is much easier with the alloy due to the fact that pieces stay shiny longer. She also points out that since most customers aren't excited about the care and cleaning of jewelry, eliminating the need to wipe down pieces is a definite plus.

Additional Resistance

Much like adding germanium to sterling fabrication alloys can help them resist tarnish, adding zinc and silicon to casting alloys can help protect against firescale. The bane of many a silversmith, firescale frequently appears on sterling silver when heat is applied in the presence of oxygen, leading the copper to turn a reddish-purple color. While it can occur while the alloy is being heated at the bench, it normally happens during the casting process, where it can form not only on the surface, but also deep within the metal, waiting to be discovered during polishing.

"After casting, sterling silver will have a black coating on the surface," explains Aithal. "It comes off after pickling, but it may leave a hint of pink at the surface. Pickle will remove that copper oxide on the surface, but not on the inside. If copper oxides were colorless like the oxides of silicon and germanium, we would not be discussing firescaling of sterling silver at all!"

When it does occur, the only option is to remove it, usually by polishing or filing, but even then it involves having to remove material down to the root of the firescale, which in some cases can be substantial.

It's no wonder then that firescale has turned off many a jeweler to traditional sterling silver. It was one of the main reasons why Ronda Coryell of Ronda Coryell Designs in Albuquerque, New Mexico, stayed away from the metal, preferring to work with gold and platinum."Sterling is what sterling is, and it will have firescale," she says. "I hate firescale. It takes so much longer to make a piece."

When some of the de-ox alloys first started coming out, she tested them in her shop. "They cast beautifully," says Coryell.

"Because of the addition of these elements, there are good things we achieve (tarnish resistance), but also some bad things." -Dr. Shan Aithal, Corporate Metallurgist, Stuller INC.

Let's get together

Another thing that appeals to Coryell is the ability of some of these de-ox fabrication alloys to fuse to themselves as well as other metals. "Argentium can be fused to almost anything that has a higher melting temperature, including steel, "she notes.

Although fusing traditional sterling silver is technically possible, many experts agree that it's not practical in a typical workshop. "It's very tricky," says Aithal."You need high temperatures, but you also have to prevent it from oxidizing. It was something best left to the experts. But now with these alloys, people are finding it very easy to fuse."

When these de-ox silver alloys are heated, they start to sweat. The liquid that comes out creates a bond, allowing two pieces to fuse without oxidizing. While soldering is also possible with these alloys (and many suppliers offer solders geared specifically for them), fusing is often seen as the more practical option since it's fast and requires no cleanup.

One of the first projects Rita Marie Ross, an artist and metalsmith in Austin, Texas, tackled when she started working with Argentium was to make three identical rings in the metal. "I sat them down on top of each other, heated them up, and fused them together," she says. "It happened so fast and perfect—that's a wow factor! Once they're fused, they won't move. And the beauty is that there's no solder so you don't have to clean anything."

"It happened so fast and perfect- that's a wow factor! Once they're fused, they won't move. And the beauty is that there's no solder so you don't have to clean anything."  -Rita Marie Ross

These alloys' ability to be fused also opens up the door to easier granulation. Unlike with fine silver granules, which have to be heated to an exact temperature or risk being melted, these alloys have a broader temperature range that allow the de-ox granules to fuse long before melting is a possibility.

However, Binnion points out that fusing these alloys can result in weakening the metal. "When you heat it up to fuse, you're growing the grain structure radically, making it a less strong material," he warns. "If you're doing a lot of fusing, the material can get weaker and be prone to breaking. It's a tradeoff you have to make with these alloys."

Working it over

Even with all the great properties these de-ox alloys offer, many jewelers may be hesitant to try them because they've heard that the fabrication alloys can't be worked in the same way as traditional sterling silver. However, it's not too hard to adjust from traditional sterling to a de-ox alloy; you just need to be aware of the differences and how to accommodate for them.

A Hard Time. The addition of elements such as germanium, zinc, and silicon reduces the mechanical strength of the de-ox alloys. "Some of these alloys remove all the copper or at least the vast majority of it," says Binnion. "The problem with this is that the copper addition is what gives sterling its strength. This means all the de-ox alloys are soft when compared to standard sterling in the as cast, annealed, or work-hardened condition."

While these alloys may start out softer than sterling silver, they can be precipitation (or age) hardened  to improve their mechanical strength. Since each alloy has its own unique formulation, it's best to follow the alloy manufacturer's instructions for age hardening.

The Flux Factor. Many of these alloys can be easily fused, but flux is recommended to avoid the formation of a superficial oxide layer. In addition to keeping the joint clean for fusing, the flux can serve as a helpful indicator for knowing when the piece is approaching the correct temperature to fuse.

When Ross is fusing a piece of Argentium, she keeps an eye on both the color of the metal she's heating as well as the flux that she's applied to the joint. "You have to look closely when you're heating

it because it's not as blatant as with solder, where you see a line of silver flowing," she says. When the metal starts to turn orange and the flux turns into what she can best describe as "dancing droplets," she knows it's time to pull up her heat.

While flux is only necessary on the joint you're fusing, if you're doing multiple fusings on a piece, Coryell recommends applying flux to the entire piece.

Support Is Critical. The same elements that improve these alloys' tarnish and firescale resistance can also have unintended consequences. "Because of the addition of these elements, there are good things we achieve (tarnish resistance), but also some bad things," says Aithal. For one, a piece needs to be fully supported when it is being heated.

"When you're annealing at the bench, inside of the piece some areas can become liquefied, and therefore the metal loses its strength," explains Aithal. "You have to support the piece, otherwise it can sag and crack." Luckily, that support can be as simple as a charcoal block.

"It's really an issue of knowing what you want to do. Then find and learn everything about the best material for your needs so you can produce the best quality product with it." -James Binnion

A Hands-Off Approach. Many jewelers experienced with traditional sterling will have to learn to wait a bit longer after heating a de-ox alloy. While sterling silver is also susceptible to cracking when red hot, the de-ox alloys tend to take longer to solidify, and they remain fragile for longer: If you handle them or apply pressure too soon, they could crack.

How much longer to wait will ultimately depend on the alloy and type of piece being heated, but many experts say that it's usually not more than a difference of a few seconds. And, when in doubt, there's no harm in letting the item cool a bit longer to be safe.

Keep It Clean. It's recommended that when working with de-ox silver alloys, you use a dedicated set of polishing wheels for the metal. This prevents cross contamination from other metals that can get deposited on the silver and disrupt the formation of the protective oxide layer.

And remember: No alloy is perfect. "It's really an issue of knowing what you want to do," says Binnion. "Then find and learn everything about the best material for your needs so you can produce the best quality product with it."

Ready to give these alloys a go? To help you determine which one may work best for you, visit MJSA.org this month for a breakdown of the different casting and fabrication de-ox silver alloys available to the industry.