IDing metals in jewelry

Jewelry Discussion
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I inherited several hundred pieces of mostly costume jewelry going way back and have been enjoying learning about all the famous and not so famous designers and companies of the past. And some of the pieces have really interesting stories behind them. Investigating individual pieces on-line eventually led me to sites where you can buy used jewelry for ridiculously low prices (by the pound basically). Well… so that led to a several hundred more pieces of jewelry. And of course, some of that stuff is junk, not particularly worth anything (and even possibly hazardous to ones health if it is made mostly of lead and plastic as much modern costume jewelry is).

Well… it is now time for me to downsize and concentrate on my own jewelry (finish off all those pieces I’ve started and the long list of ones I’ve designed but haven’t even started yet), which means that I need to figure out what these things are really made of, so that I can sell or dispose of them responsibly (by the way, some of the vintage jewelry is absolutely gorgeous and obviously handmade - and it practically made me cry to think of the jeweler’s whose absolutely gorgeous work is apparently not valued any more (some of the cloisonne and handmade glass pieces are unbelievable) Moreover, I can understand after having looked at some of what is currently being sold why there is a good market for good vintage or antique costume jewelry since the manufacturing was often quite astoundingly good!).

I have been using an acid testing kit which includes not just acids for various percentages of gold, but also acids for silver, platinum and palladium and nickle. Moreover, I know how to use these to determine if a non-precious metal is copper, brass, lead, tin, etc. And as you might expect I have a good magnet as well as 2 sets of gold and silver testing needles.

However, every so often I run into a metal which is not magnetic, yet doesn’t react to any of the acids. It is usually shiny white (and I can’t get it off my testing stones with anything). From the testing kits one might think that it is platinum; and it usually seems quite solid and heavy. But I am not convinced… especially with brutalist or brutalist revival pieces. However, since these are actual pieces of jewelry some of the other kinds of tests that I’ve read about on this forum aren’t possible (e.g., specific gravity, heating to see if it melts at a reasonable temperature, etc.) - at least not without destroying the piece (and I hate destructive testing). Worse yet, these pieces are often missing any kind of identifying information (and I’ve become pretty good at finding and looking up makers marks and such).

While I live near a University, a school of mines even, I don’t think now is a good time to ask if I could get someone to help me (what with everybody’s grants having been cancelled), and all the advanced equipment I’ve seen on-line at sites like ishor.com are way outside my price range.

Any thoughts about other non-destructive tests I can try before I stick my neck out and claim that a piece of jewelry is something that it might not really be?

I also note that I have started taking some of the stone identification classes as well (e.g., from GIA) so I am trying to cover that side of the field as well; but I think that will take even more time! And yes, I do have a basic set of equipment for that as well (refractometer, MOS hardness test stuff, etc.) though nothing too sophisticated. I’d love to have a good spectrometer (better yet a mass spectrometer) but …

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You can easily test the specific gravity of metals at home, and the method is both nondestructive and surprisingly accurate. A small hydrostatic weighing station is simple and inexpensive to build. It lets you weigh a jewelry piece in air and then in water on the same scale, reducing handling errors and improving consistency, which is especially useful for small items like rings or pendants.

If a piece contains stones, these will need to be removed. You can measure stones separately, though that’s more delicate work.

To set up your own station, start with a digital scale that reads to at least 0.01 grams and has a flat weighing pan. You’ll need a small beaker or glass of water, a lightweight stand or support that fits over the scale, and a thin wire, fishing line, or even dental floss to suspend the jewelry. A cut-down plastic water bottle makes a good beaker. The stand should be tall enough for the jewelry to hang fully underwater without touching the bottom or sides.

For better precision, weigh the wet string or line separately and subtract its weight from the total; that part that will be in the water, that is. Once the setup is ready, place the stand over the scale and set the beaker of water on it. Make sure everything is stable. Suspend the jewelry from the scale’s weighing hook (many scales have one under the pan) or from a small rod attached to the platform. Tare the scale to zero with the entire setup in place. Weigh the piece in air and record the result as W₁. Then submerge it fully in the water and record the new reading as W₂. Calculate the specific gravity using SG = W₁ ÷ (W₁ – W₂).

Very simple…

Use distilled water at room temperature for best results, and make sure the item is clean and free of air bubbles. If bubbles form, add a drop of dish soap or dip the piece briefly in alcohol. Ensure the piece isn’t touching the sides.

This simple hydrostatic setup produces reliable results and can be built from common household items. For anyone who works with or collects jewelry, it’s a practical and accurate way to identify metals. Tables listing the specific gravities of most metals are easy to find online or in books such as The Complete Metalsmith by Tim McCreight.

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I would hazard a guess that those pieces are made of Monel. Invented in 1905 and trademarked in 1921, it is an alloy that is resistant to corrosion and acids, is very hard, and difficult to work.
The Wikipedia article is very informative.

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Regarding SG determination, I learned a simplified procedure a few years ago at a Faceting Symposium. Using a small pocket carat scale and a small plastic salad dressing cup, fill the cup with water and set it on the scale and tare to zero. Use a small piece of string of nylon cord to tie to the article to be weighed. Immerse the article suspended in the water and note the weight of the water displaced. Then let the article rest on the bottom of the container and record the weight of the article. Do the division to get the RI. -royjohn

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In my description of SG determination, I mis-typed….the last sentence should say “Do the division to get the SG [not RI].”

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Platinum does react with concentrated aqua regia. It won’t react with concentrated nitric or hydrochloric acids alone. a 3:1 mixture of HCl + HNO3.. it’s the only acid that will attack PGE metals and pure gold. If your acid test kit contains aqua regia, use it with EXTREME caution.. A metallurgist from the School of Mines in your home time might be able to identify it by sight or at least narrow down the possibilities. The specific gravity of Pt is also higher than pure gold.. Monel metal will be attacked by ammonia and nitric acid. XRF is sometimes used by local retail precious metal and coin dealers to check the purity of precious metals and coins. EMPA can’t be used directely on Pt. metal. LA-ICP-MS is far cost prohibitive even if can been done at your local School of Mines.