Cynthia Eid SNAG News Technical Article by Cynthia Eid: Argentium Sterling Silver |
The Society of North American Goldsmiths
TECH NEWS
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a darkened area, of course). In practice, if unable to work in the dark, then wait a few moments for a small piece, or
up to a few minutes for a large piece. If in doubt, I suggest that it is better to wait longer than to be impatient. The worst
that will happen by waiting is that the metal will be a bit harder. I find that it is still wonderfully ductile and malleable,
even if I air-cool it without quenching. If I were doing soldered constructions that I did not want to warp, I would air cool,
not quench. In fact, I rarely quench any metal—it is my general practice is to avoid shocking any metal that I am
working with—unless it is one of the gold alloys that require quenching, or a steel tool that I am making. On the other
hand, note that the sooner the Argentium® Sterling is quenched, the softer it is—therefore, you may choose
between softness and risk of shock-cracks or warping according to the situation and your personal sense of
concern about those factors. MELTING TEMPERATURES Regular sterling silver has a solidus melting temperature of 1475ºF and liquidus flow point of 1650ºF. (Solidus is the temperature at which a metal starts to melt; liquidus is the temperature at which a metal is fully melted.) The solidus melting point of Argentium® Sterling Silver is 1410ºF; the liquidus flow temperature is 1610ºF. CASTING (Since I don’t do my own casting, the following is information gleaned from experts such as Peter Johns.) Argentium® Casting Grain is 93% silver, with the same solidus and liquidus as Argentium® Sterling sheet and wire. Pyrometric temperature control is preferable, because it is important not to overheat when melting Argentium® Casting Grain for casting. If a torch must be used, one needs to learn to recognize the paler color that indicates Argentium® Sterling is melting. To avoid contamination from other metals, use a separate crucible. Do not use silicon carbide. When investment casting, a pour temperature of 1740–1780ºF (950–980ºC) and a flask temperature below 1250ºF (677ºC) is recommended. A protective atmosphere is preferable, but the use of boric acid flux or graphite powder is effective. After casting the metal, a minimum of 15 minutes air-cooling is needed before quenching. Note that castings will be much harder if they are completely air cooled, rather than quenched. As with most metals, re-melting scrap may result in brittle castings. SCRAP If you generally send your scrap to a refiner, it is not necessary, at this time, to keep Argentium® Sterling scrap separate from regular sterling scrap. (It won’t be detrimental to regular sterling. If Argentium® Sterling is mixed with regular sterling, the sterling’s properties won’t alter until the percentages of the alloys become similar to those of Argentium® Sterling.) HALLMARKING Jewelers and silversmiths who wish to use the Argentium® Silver "as" mark may go to ( www.argentiumsilver.com ) for a license application form. Since Argentium® is sterling silver, the only legal requirement is to stamp it as "925" or "sterling silver." SOLDERING Because of the lower melting temperature, hard solder is not recommended for use with Argentium® Sterling Silver. Medium, easy or extra-easy regular silver solders are safest. In practice, I find that I can |
use hard silver solder if I really want to for a short seam in a complex construction, though when I do so, I often
notice that the metal shows signs of looking like it came close to melting. Germanium-containing solders have been developed. I have tried them out, and I like the color match, as well as the fact that they flow well, with good capillary action. Their melting temperatures are approximately equivalent to medium, easy, and extra easy. The new solders are expected to be available in June. Available as wire and sheet, they will be called Argentium®Hard, Argentium® Medium, and Argentium® Easy. Argentium® Easy melts at 1146ºF (619ºC), and flows at 1253ºF (678ºC). Argentium® Medium melts at 1237ºF (670ºC), and flows at 1319ºF (715ºC). Argentium® Hard melts at 1272ºF (689ºC), and flows at 1355ºF (735ºC). Currently, Argentium® Sterling Silver is supplied annealed, which is wonderful for me since I rarely use a piece of metal without forming it a bit first. Straight planes of metal are uncommon in my visual vocabulary. It is great to be able to start forming without needing to anneal first. I love it that I can move the metal farther before it needs annealing. For me, the only problem I’ve had with soldering is remembering that Argentium® Sterling does not conduct heat as well as regular sterling does. This means that I approach soldering Argentium® Sterling similarly to the way I solder gold (or the way a beginner wants to solder). After giving the entire piece a bit of a general heating, I concentrate the heat on the solder joint (the area that is being soldered —not the solder itself). Metalsmiths who like to make soldered constructions of flat sheet may find that they need to prepare the metal a bit beforehand to prevent the metal from sagging during soldering. Lay the Argentium® Sterling on a flat soldering surface, bring it to annealing temperature (dull red) with a torch flame, keep it at that temperature for about 15 seconds, and then allow it to air cool. There is disagreement amongst the experts on just why this sagging occurs, and why annealing then air-cooling helps prevent sag. It has something to do with crystaline structure, the size of the grain, and the rate of cooling. More studies are being conducted; I bet that eventually the manufacturing process will be adjusted, and that this is a temporary problem. In the meantime, note that the lower the temperature of the solder, the less that sagging is a problem, and that sagging is only a problem with unsupported flat metal. T. Flory recently ran a set of experiments that expanded on the tests that I have done. They can be seen on his blog at RETICULATION? Noticing the texture it gets when close to melting, I tried to reticulate Argentium® Sterling Silver. Since reticulation works on the principle of the interior melting at a lower temperature than the exterior skin, I put a few pieces of 24 gauge and 18 gauge Argentium® Sterling sheet into a kiln for 45 minutes at |
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This technical article was first published by the Society of North American Goldsmiths in its newsletter, under Tech News. All SNAG members automatically receive the newsletter five times a year. To sign up for membership, go to www.snagmetalsmith.org, or (630) 778-6385.
| Cynthia Eid |
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