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 On the testing of precious metals.....
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| Author | Topic: On the testing of precious metals..... |
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dragonflywink Posts: 993 |
posted 07-24-2011 01:55 PM
  
Many years ago, a jeweler friend mumbled something under his breath about "amateur idiots with gold-testing kits", and I promptly set my little touchstone test kit on a shelf, the acids surely now deteriorated with age. I have depended on marks and experience, taking anything questionable to a trusted jeweler, who uses both a specific gravity scale and acid-testing, depending on the item. Find myself constantly having to tell acquaintances with no knowledge of silver marks, that the piece that they've just scarred with drops of acid and/or file-marks, is not solid silver as their test revealed, but silverplate - perhaps even worse are those who go in the other direction, including one, who rather than doing a deep, disfiguring file mark, just clipped a small chunk off a Georgian era spoon with proper though worn British hallmarks, and put it into a puddle of acid (he was selling it and wanted to get the best price). So.....when gold hit a new high recently, I decided to sell a rather heavy unmarked Asian pendant, purchased new for me several years ago (the broken chain had been tested as 22K and sold some time ago). With my regular jeweler unavailable, I embarked on a tour of local gold buyers, with their acid tests revealing content from 18K to fine gold, the welded jump-ring as no gold content to 14K. Frustrated and a bit unnerved by the guy who said that he was going to cut a wedge out of the side, because he suspected it was just heavily plated - I visited a local buyer with a fancy state of the art spectrometer. It was a very interesting visit, and the pendant results, showing the percentages of all metals present, determined it to be just over 18K and the jump ring just under 18K (their offer was also much higher than the others). I'd brought my silver scraps along too, a group of rather ugly newish rings, from all over the world, tested as sterling or close to it, a torn unmarked coin spoon was a shade over .900 - but a surprise came with a damaged heavy cast silver Hanau spoon, marked "800" along with the pseudo-marks - it was revealed to be almost .930 fineness. A very pleasant experience, nice folks - and conversation revealed that they'd invested over $30,000. into the spectrometer because of their own expensive mistakes in acid-testing and have never regretted it, finding it was also reassuring to their clients. ~Cheryl IP: Logged |
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Scott Martin Forum Master Posts: 11520 |
posted 07-24-2011 02:56 PM
Thanks Cheryl. Here is a 2004 SSF discussion on testing silver that I hadn't thought about in a while. We used to give a presentation/demonstration on why it is a bad idea to do acid testing. We had a nice touchstone kit (stone, needles & acids) in a nice cedar box. We did our last "acid testing is a bad idea" presentation many years ago and we put the acid testing kit away. Last week, while looking for something else, I came upon the old acid testing kit. The box was completely crumbled, the needles corroded and fused together, the stone and the empty acid bottles were all that could be salvaged. And the shelf was partly eaten away. For anyone who might have a languishing acid testing kit, check on it and get rid of it. IP: Logged |
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Gaspare Posts: 97 |
posted 07-28-2011 12:33 AM
Trying to find out some counterfeit pieces I brought some suspicious pieces to a pawn shop in NYC.. The ring was stamped 800,,when tested with his new machine it tested sterling/925. Good enough for me. - commonly the counterfeiters will reproduce a piece near perfect but make it in 'todays' silver 925 and stamp it with 800 or 835 then age it etc.. - overall he says his new machine is a lifesaver as they are getting more and more precious metal in every day, it's quicker and this takes the guess work/ filing, acids, stones explanations to the customers out of the equation.. [This message has been edited by Gaspare (edited 07-28-2011).] IP: Logged |
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chicagosilver Posts: 227 |
posted 07-28-2011 01:02 PM
So is there an accurate testing device or method someone can recommend that isn't dangerous, destructive, or $30,000? IP: Logged |
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Scott Martin Forum Master Posts: 11520 |
posted 07-28-2011 05:06 PM
Specific Gravity test IP: Logged |
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argentum1 Posts: 602 |
posted 07-28-2011 07:44 PM
Unfortunately just about every test has its flaws and that includes specific gravity. Is the water distilled or not. Is it cold or hot. Has the item been configured and plated to mimic an actual silver item. Specific gravity and acid test have been used for years and buyers of precious metals have gotten along just fine so not to worry. If you want to worry then spend the $30.000 and buy yourself a spectrographic analyzer. but then you will have to learn how to use it and interpret the results. IP: Logged |
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salmoned Posts: 336 |
posted 07-29-2011 04:58 AM
Specific Gravity tests do have limitations, but 'distilled water or not' and 'hot or cold' are not among them - a proper test involves testing known item(s) under the same conditions as the test piece and adjusting values accordingly. IP: Logged |
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argentum1 Posts: 602 |
posted 07-29-2011 09:46 AM
No arguements just a follo-up comment. I passed that along to my wife of 40+years and 32 years as a Biochemist and all I got was 'believe what you want'. You are correct in that as long as all conditions are identical then your results should be reliable. It does help to verify using a known. [This message has been edited by argentum1 (edited 07-29-2011).] IP: Logged |
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dragonflywink Posts: 993 |
posted 07-29-2011 10:33 AM
Really posted this because of the wide variances in fineness found by the tests on the pendant, my fascination with the spectrometer, and my surprise at the high silver content of the Hanau 800-marked piece. Wasn't promoting any method over another, but struck me as quite interesting that folks who are making their living in precious metals had such widely varying results from their acid-tests. Concerning spectrometry, which has been used by assay offices and mining concerns since the 1930s, there are much less expensive (though still pricey) units available, guessing that they are not as precise as the unit I saw in use, which required no interpretation - the computer provided an extremely detailed, but easy to read analysis. I also see a number of people around here checking jewelry at shops, sales, etc. with little hand-held gold and gemstone checkers, no idea if they are accurate, but their users seem to trust them. As said, my jeweler has a specific gravity scale, which also does all the calculations for him, but it does have limitations, he uses it for both metal and gemstones, however it can't be used when the stones are set into the metal, and the size of its tank limits it to fairly small pieces in regards to silver flatware or holloware (haven't tried specific gravity testing on my own). ~Cheryl IP: Logged |
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salmoned Posts: 336 |
posted 07-29-2011 05:59 PM
Don't be fooled by precision instruments - if not properly [and periodically] recalibrated using known, standard samples, accuracy is suspect (5 figure precision may be limited by 2 figure accuracy, or worse). A proper assay will include the dates and adjustment range and results for the last 3 recalibrations of the instrument (or a statement concerning recalibration, at least). [This message has been edited by salmoned (edited 07-29-2011).] IP: Logged |
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cbc58 Posts: 333 |
posted 04-06-2019 09:33 AM
A question regarding a piece that has been acid tested: can all trace of the acid test be removed without causing harm to the piece -- or is the piece forever compromised ? Can you in fact remove all signs of an acid test so that it will never reappear over time? IP: Logged |
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Scott Martin Forum Master Posts: 11520 |
posted 04-06-2019 01:37 PM
Acid dissolves some silver. Its gone for good. The item is now less than before. If silverplate then the base metal is now exposed. If solid silver the buffing (which removes more silver) might hide some of the damage. But a trained/experienced eye can usually tell IP: Logged |
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ahwt Posts: 2334 |
posted 04-07-2019 02:58 PM
The Birmingham Assay Office no longer scrapes metal off the object to be tested, but instead uses X Ray Fluorescence as an alternative assaying method. This way no metal is scraped off and no refinishing is required. The Germans cut a zigzag line to take some silver to test and no one there seemed concerned about covering it up. It just becomes part of the history of the object. IP: Logged |
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