Submitted by sylpher250 t3_z1bdkg in askscience
Stemming off of this article: https://people.com/human-interest/man-with-metal-detector-discovers-medieval-wedding-ring-worth-an-estimated-47000/
What kind of property change would the gold go through if melted today and made into another ring?
Couldn't that corrosion be faked by some chemical process though?
Also, wouldn't storage conditions change corrosion rates substantially.
Corrosion could be induced by putting the gold in a more oxygen rich environment and perhaps making it a bit moist, but it's unlikely that an authentic corrosion profile could be forged. The paper I was using as a source mentions:
"Despite its chemical stability, gold possesses a rich oxidative electrochemistry resulting in the formation of gold oxide coatings and, in the presence of complexing agents, oxidative dissolution processes. Such electrochemical processes are sensitive to changes in the textural properties of the metal surface, reflecting most minute alterations of
the gold surfaces upon aging."
This indicates that it's not just the corrosion that is important, but rather the corrosion and the fine mini reactions.
For your second question, yes storage conditions change corrosion rates substantially. However, this can be accounted for chemically (acidic soil vs basic soil, wet vs dry, etc). This plays a part in the "presence of complexing agents" quoted earlier.
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As well, the authors used known specimens as calibration standards. Those specimens were in various storage conditions, so can be compared to new specimens found in similar conditions.
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The style of the ring or the quality of manufacture might be characteristic of a particular historic period. An expert might be able to distinguish a Tudor era ring from an Anglo Saxon era ring from a Roman era ring.
It's conceivable that if the ring has a stone set in it, perhaps there's a bit of wax or resin used to hold the stone in place while the setting is adjusted. If there were, it might be possible to carbon date it.
The gold itself of course is ancient, probably older than Earth itself.
If you melt down a Tudor ring and make a new ring, or even just hammer the ring into a new shape, it won't be a Tudor ring any more and there won't be any evidence it ever was one.
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At one time, dental gold was amalgamated with lead and mercury. Gold taken from the mouths of many victims of the holocaust (Shoah) had lead/mercury amalgams. If the gold item in question has quantifiable amounts of lead and mercury then it is likely a 20th century construct.
What the lead and mercury isotopes are and what the concentration would need to be in order to identify it as dental gold is beyond me.
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That is actually a great question! Jewelry is appraised at the weight of the metal plus gems, right. However value comes from history. For example, if you have great grandma's ring that she was given and she went through struggles and turmoil, specifically historically relevant events, that the ring survived. You eventually got that ring. The price to duplicate is x dollars, however, because of its history you are able to ensure it for far greater value, because the ring cannot really be duplicated anymore. The craftsmanship of that time, the methods of production, the history significance, cannot be duplicated.
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What about something like the ring in the article? It was just in a field, underneath dirt, no traceable lineage, yet it was determined to be hundreds of years old.
vickyswaggo t1_ixb4ier wrote
https://chemistry-europe.onlinelibrary.wiley.com/doi/full/10.1002/celc.201800435
This is an archaeology paper from 2018 discussing one method of dating archaeological gold. I'm unsure if it's open access because I'm accessing it from my college campus, so I shall summarize it:
The authors use a corrosion clock and electrochemistry (specifically something called VIMP which stands for voltammetry of immobilized particles). Gold forms oxides, which can be studied with electrochemistry. The authors designed a "calibration curve" using known compositions and then fitted historical samples onto this curve.
You mentioned the possibility of melting and recasting. When a metal is melted, the metal oxides decompose into the metal and oxygen. Specifically for gold, Gold (iii) oxide can form. It decomposes at 298°C. Gold melts at 1064 °C. As you can see, gold (iii) oxide would decompose long before the gold itself could be melted.