Dating Metals?

[Michael Blalock]

Is there an empirical means to determine the age of a metal object? Can the determination be made by the patina or chemical make-up of the corrosion? In this case it’s copper or a copper alloy I’m looking for. I'm talking about millennia here, not years or centuries.

[Rivkin]

In short - no, it can not. The only analysis I'm aware of is some basic empirical comparison to other pieces of the same age while asking a question "does this rust looks natural - like in other pieces of the same time ?".

[fearn]

Hi Michael,

If you're thinking about millenia, then I'd suggest carbon-14 dating of any carbon containing compound that's positively associated with these specimens. In other words, talk to an archeology department at a nearby school and find out where they do their dating.

F

[ariel]

I am not sure carbon dating will work.
It is based on uptake of C14 by a living organism . As soon as the organism dies, it stops absorbing carbon at all and then we can measure the ratio of C14 : C12. From this number we can calculate the age of the remnant knowing the rate of decay of C14 into C12.
Metals are not living creatures. Alloys such as steel were prepared using carbon existing at the time of manufacture and the dating will reflect the age of, say, coal(several millions of years) or wood/leaves (days to tens of years). If I use coal made out of 500 yo wood (such as many olive trees), the sword made in 2005 will reflect the age of that particular wood.
Also, the precision of the method is too crude to be of major help to us: it is relatively easy to distinguish an object that is 2,000 years old from the one that is 100 y.o. However, we are mostly interested in "is it 19th or 18th century?" type of questions. That falls well below the assay limit of resolution.
Ann Feuerbach would know the answer much better and correct me if I am ignorantly wrong.

[Michael Blalock]

I was thinking along the lines of 2000 years old vs 100 years old. I have a South Arabian bronze sculpture that must be 1500+ years old which i am certain is not a fake.
I would think this situation comes up often with bronze swords that may be ancient vs. fake. Especially with all the replica bronze swords from china on eBay. I take it from the answers that they only way to make an educated guess is to have someone with lots of experience examine the bronze and compare the condition of the metal to known pieces.

[fearn]

Hi Ariel,

To be more precise, I was thinking of an archeological situation, where charcoal from an old fire, the rags wrapping a statue, or some other source of organics were found with the statue. Or there were remnants of a wood hilt on an old knife.

If it's a statue that was found in an antique shop, forget about it. I suppose you can get some estimate by observing rates of corrosion in an environment similar to whatever it was in for the last two millenia, but absent that, it's wild-eyed (ahem) guess time.

F

[Michael Blalock]

Thanks for all the information. Here is a photo of the little fellow I am talking about. He came from Yemen and has been handled a lot for the last 35 years so some of the patina has worn off, especially on the nose were bits of the copper alloy are showing through.