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10/4/2012: Argentium Guild Newsletters
Firescale-Resistiant Sterling Alloys Tested
Argentium® Sterling Silver, a registered and patented alloy developed by Peter Johns, is currently being produced by Stern Leach in the U.S. under a licensing agreement from Middlesex University, England. Argentium® Sterling Silver is a registered trade name.
The addition of germanium to standard silver is a patented process licensed under Patent Nos. US 6,168,071, GB 2255348, GB 2283934 and European Patent No. 0729398.
This page has been produced to provide technical information on how to work with the Argentium® Sterling Silver. Argentium® Sterling Silver has dramatically better tarnish resistance than standard sterling and will not firestain. This alloy requires minimal maintainance. An occasional wash and rinse and/or wipe with a soft cotton cloth is all that's needed to keep the object in pristine condition. Manufacturers will no longer be deluged with store returns requiring refinishing.
Argentium® Sterling Silver contains at least 92.5% fine silver. The law states that sterling MUST contain no less than 92.5% fine silver with the remainder being any other metal.
Argentium® Sterling Silver complies with safety standard ISO 8442-7 (a safety standard for: "Materials and Articles in Contact With Food Stuffs, Cutlery-Table Holloware"). Part 7 indicates the section for precious metals. Sterling cutlery manufacturers quote ISO 8442 in catalogs for sterling silver and silver plated cutlery.
Argentium sterling can be worked using the same common sense precautions you would normally employ working with standard sterling. Argentium® Sterling Silver MSDS can be found here.
My first experience using this alloy was with an unrolled ingot 5/8" wide x 4" long x .450" thick. I had decided to make a ladle, working this piece of metal to death without the use of flux to protect against firestain. I hot-forged the ingot twice, then 20 annealings, quenched, and worked the ingot cold. I felt this would be the prefect test see just how firestain resistant it was. The primary difference was judging the temperature during annealing. I witnessed a distinct difference in color; it was a very pale red glow that showed. This alloy has a melting temperature about 60 degrees below that of standard sterling, so bringing it up to a standard sterling annealing color would be too high. There is the need to allow the Argentium® Sterling Silver to "rest" before quenching or forging since it tends to be a bit brittle at this temperature.
The alloy filed and abraded with silicon carbide wet-dry paper like standard sterling, perhaps a bit softer, though, you could run over the ladle with a tank without worry of distortion. The real test was to come! How would this horribly abused piece of metal hold-up to firestain? Well, I was admittedly skeptical at first, as any silversmith would be. I polished the ladle for what seemed to be an eternity, thinking that I would eventually see that wretched purple stain. It simply didn't appear! I was laughing inside as I polished, thinking that this alloy would revitalize the use of silver. I examined the surface under a 10x loupe to see if there were any irregularities in the surface...it was as perfect as standard sterling.
The ladle below has been displayed among standard sterling pieces. I have witnessed no dramatic change in its color, and its almost pristine state has been in stark contrast to the now dark brown silver objects surrounding it. After a one-year span of time, normal dust and finger marks on the ladle were easily removed with tap water and a cotton towel!
When used for spinning, the Argentium® alloy feels harder than conventional alloys; this may seem a drawback but in practical terms does not make the alloy less ductile. In practice, better reductions can be obtained between each anneal. The Argentium® Sterling Silver may slightly discolor during annealing. Silver polish or a brass/nickel wire brush and hand soap will remove this discoloration.
The improved ductility offers good spinning and press work properties, plus an amazing firestain resistance (firestain is caused during torch annealing and soldering). Firestain resistance reduces the amount of polishing required and eliminates the use of hazardous stripping chemicals.
When raising the alloy you'll find it "moves" a bit easier than standard sterling, resulting in increased production and a good finished hardness.
Firestain resistance is also obtained in items made from Argentium® Sterling Silver casting grain. High definition investment castings can be produced using slightly lower melting temperatures than for standard sterling. Recommended casting temperature 1725°-1750° F (940°-955° C). When only the eye is used, care should be taken not to overheat the alloy. Super- heat will only burn off essential components in the alloy. When the alloy is ready to cast, it will demonstrate a lighter red than standard sterling. Casting machines equipped with infrared heat sensing must be calibrated for Argentium® Sterling Silver as the germanium in the alloy will give a false reading. Flask temperature should suit the size of the item being cast (as always). Allow the flask to cool for at least fifteen minutes or until the flask is cold before removing investment.
When reusing previously cast material, a ratio of 1/3 previously cast and 2/3 new material should be mixed.
The addition of germanium to sterling silver changes the conductivity of the new alloy, compared to standard sterling silver. The International Annealed Copper Scale (IACS) is a measure of conductivity in metals. On this scale the value of copper is 100%, pure silver is 106%, and standard sterling silver 96%, while a sterling alloy containing 1.1% germanium has a conductivity of 56%.
The significance of this is that the Argentium® Sterling Silver does not dissipate heat and energy as quickly as standard sterling silver. This may be an advantage in that it is possible to use a more localized flame when carrying out soldering operations. The disadvantage is that a piece will take longer to cool and, therefore, require more care to not damage the piece by handling it when it is too hot. Remember, the alloy shows a much paler color than standard sterling at the same temperature.
As previously stated, Argentium® Sterling Silver will have a slightly different color than standard sterling when heated. It is advisable when annealing or brazing to do so in darker surroundings. Since the alloy will anneal and braze at a lower temperature, it would be difficult to judge the color. As is good practice for annealing sterling silver, torch annealing of the alloy should be carried out at a temperature equivalent to the first signs of red heat. It is also important that the work should not be moved or quenched until red heat is no longer viable. If items are quenched too quickly, cracking will appear.
When brazing/soldering, it should be noted that the addition of germanium lowers the melting temperature of the alloy by 59°F (15°C). It is recommended that a "medium" grade is used for seaming, with "easy" and "extra easy" grades used for further assembly. Hard silver solder can also be used, though, more care must be taken. Solders containing germanium, which will give better tarnish protection are currently being researched.
To avoid residual oxide contamination, clean pickle and clean fire bricks are important when working with Argentium® Sterling Silver.
The standard sterling sample above shows firestain that has penetrated 20-26 microns after annealing in a kiln at 1076°F (580°C) for 60 minutes-an extreme test! The Argentium® Sterling Silver, when exposed to an identical environment, shows a cupric oxide (black) layer only 1-2 microns in depth, therefore, it can be removed by pickling. A similar surface oxide would be seen on low carat gold alloys when they are annealed. These oxides, which are easily dissolved in pickle, do not penetrate like firestain on standard sterling. In normal workshop practice with Argentium® Sterling Silver, depending on how the flame of the torch is used, some areas of the alloy may blacken slightly on the first anneal. This surface oxide can be easily removed with pickle and the surface of the alloy will then be protected during subsequent heating by a layer of transparent germanium oxide.
Pure silver is unique in the way it allows oxygen to penetrate through it, especially when heated to high temperatures. In standard sterling, this allows the copper deep in the alloy to be oxidized, which must then be removed by time consuming or dangerous measures i.e. chemical bombing or buffing. The pickling of standard sterling only removes firestain from the upper-most layer, leaving a surface of pure silver. During further annealing and brazing, the oxygen penetrates this pure silver layer, allowing the formation of firestain at a depth that pickle cannot remove.
Fusion welding has been a mainstay in the jewelry for many years, and Argentium® Sterling Silver works well with this technology. Fusion provides a fast, clean bond between similar & dissimilar metals when using fusion findings. A large capacitor is used to store an electrical charge, like a battery. That charge is released through a fusion finding as it touches the surface of the receiving metal. A small explosion occurs which blows off all of the oxides and gases away from the weld. For the next millionth of a second a vacuum exists, allowing similar and dissimilar metals to bond in the residual heat. There is no metal distortion, discoloration, or heat produced using this process. The Sparkie® is one of the more notable fusion welders in the jewelry trade.
Resistance welding is also effective using Argentium® Sterling Silver. A current is passed between two current-carrying electrodes and the parts to be joined. External pressure from the electrodes is used to produce contact between the parts and subsequently to consolidate the joint. Unlike fusion welding, resistance welding produces a slightly sunken area from the electrode contact points.
Argentium® Sterling Silver is precipitation hardenable. A doubling in final hardness can be achieved by heating at temperatures obtainable in a domestic oven. The hard alloy can be softened by conventional annealing and then hardened again if required. The alloy's hardness can also be doubled after the piece you're working on has been work hardened: 450°F (232°C) for @2 hours, 570°F (299°C) for @30 minutes. The alloy will not lose its hardness if left in the oven beyond the above times.
In order to avoid cross-contamination when polishing Argentium® Sterling Silver, buffs/mops which have been used on metals other than sterling silver should not be used. For polishing, JacksonLea aluminum oxide cut-down #303 and C-3568 rouge compounds work well. Previously used buffs/mops should be thoroughly cleaned by raking. It is also important that cleaning processes such as ultrasonic baths not allowed to become contaminated. Cleaning agents and ultrasonic cleaning solutions should have a neutral pH value.
Scrap Argentium® Sterling Silver may be sent to any refiner for processing, though, the germanium would not be recovered.
Argentium® Sterling Silver has the following advantages over conventional sterling alloys:
I'll continue sharing my experiences using this alloy, so check back occasionally.
Germanium, symbol Ge, hard, brittle, grayish-white, crystalline semimetallic element. The atomic number of germanium is 32; it is in group 14 (or IVa) of the periodic table.
The Russian chemist Dmitry Mendeleyev predicted the existence and chemical properties of germanium in 1871; because of its position under silicon in the periodic table, he called it ekasilicon. The element was actually discovered in the silver-sulfide ore argyrodite by the German chemist Clemens Alexander Winkler in 1886.
Germanium is in the same chemical family as carbon, silicon, tin, and lead, and resembles these elements in forming organic derivatives such as tetraethyl germanium and tetraphenyl germanium. Germanium forms hydridesgermanomethane, or germane (GeH 4); germanoethane (Ge2H6); and germanopropane (Ge 3H8)analogous to those formed by carbon in the methane series. The most important compounds of germanium are the oxide GeO2 (germanic acid) and the halides. Germanium is separated from other metals by distillation of the tetrachloride.
Germanium ranks 54th in order of abundance of the elements in the earth's crust. Germanium melts at about 937°C (about 1719°F), boils at about 2830°C (about 5126°F), and has a specific gravity of 5.3; its atomic weight is 72.59.
Germanium occurs in small quantities in the ores of silver, copper, and zinc, and in the mineral germanite, which contains 8 percent germanium. Germanium and its compounds are used in a variety of ways. Suitably prepared germanium crystals have the property of rectifying, or passing electrical currents in one direction only, and so were used extensively during and after World War II (1939-1945) as detectors for ultra-high-frequency radio and radar signals. Germanium crystals also have other specialized electronic uses. Germanium was the first metal used in the transistor, the electronic device that requires far less current than the vacuum tube. Germanium oxide is used in the manufacture of optical glass and as a drug in the treatment of pernicious anemia.
Microsoft® Encarta® Online Encyclopedia 2000