Researchers Spot Fake Ancient Pottery Using the Earth's Magnetic Field

thangalin 2 hours ago | parent | next [-]

https://impacts.to/downloads/lowres/impacts.pdf#page=23

Quoting my book:

"Studying these layered strata is known as magnetostratigraphy and can be used to verify radioactive dating methods. Geologists used magnetostratigraphy to cross-check the dates of the Nakali Formation, where Nakalipithecus nakayamai’s jaw was found."

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userbinator 2 hours ago | parent | prev | next [-]

Because the location of the pole is constantly shifting, the TRM of ancient pottery points in a slightly different direction than that of pottery made today.

Did anyone else have a strong "WTF?" reaction upon reading that sentence? Yes, the pole has moved. No, it's completely irrelevant given that not every piece of pottery even manufactured at the same time is going to be fired in the exact same orientation relative to the pole.

The researchers determined that any sample older than a millennium had to be heated to at least 234 degrees Fahrenheit before its VRM was erased. New pottery samples’ VRMs, meanwhile, could be wiped at lower temperatures.

That's a more useful difference which I would attribute to the ceramics having different Curie points in their compositions, and of course it's not something too difficult to change: https://en.wikipedia.org/wiki/Curie_temperature#Changing_a_m...

Incidentally, this effect of temperature on magnetism is how the https://en.wikipedia.org/wiki/Magneto-optical_drive media records data.

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adrian_b 5 minutes ago | parent | next [-]

This was not about the magnetization during firing, but about the much weaker magnetization acquired later, while staying in the same position without being moved.

Only pottery that has not been moved for a very long time acquires a strong enough secondary magnetization. So the test distinguished pottery that has been used recently from pottery that stayed buried for centuries.

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MadnessASAP an hour ago | parent | prev [-]

We should probably assume that the authors are aware of ceramics, Curie points, and the earth magnetic field. While the article isn't very clear on what effect causes the change in temperature needed to erase the VRM. I suspect is has something to do with how long the object has spent stationary with respect to the earth's field. At least that's my takeaway from having to periodically rotate magnetometers to prevent them from acquiring a bias.

	▲	Gibbon1 3 minutes ago \| parent [-]
		I'm reminded of thermoluminescence for dating objects. Radiation creates defects in the material over time. When heated the defects release light. Imprecise but will fink on ceramics that were fired 30 years ago vs 3000 years ago. Difficulty you need to heat a fair sized sample. "Reads article" Impression, author didn't understand any of what he was told. But yes similar, over time the object picks up a faint magnetic field superimposed on the one locked in when the ceramic was made.

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flimflamm 3 hours ago | parent | prev | next [-]

What prevents forgers from generating such magnetic fields? That might be worth while if people start to blindly believing that "pottery frozen magnetic fields are not possible to counterfeit". Note that "not possible to counterfeit" is not a claim in the article.

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po1nt 3 hours ago | parent | next [-]

I would love to see such counterfeiting. The gear they would need to get and the scientists.

	▲	awesomeusername 33 minutes ago \| parent [-]
		Some wire and DC? and Claude et al

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adrian_b 2 hours ago | parent | prev [-]

From TFA:

> “So it’s hard for us to be ahead of the forgers since they can read our papers and figure out ways to trick our methods.”

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mayneack 3 hours ago | parent | prev | next [-]

The method of seems to involve hearing the artifacts which seems plausibly risky for an ancient artifact.

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profsummergig 3 hours ago | parent | prev [-]

can this clue be circumvented by using magnets oriented in a certain way around the workshop while constructing the pottery?

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comrade1234 2 hours ago | parent [-]

There are two fields. The second very weak field is acquired over centuries, I assume when the piece is not moved. The primary stronger field is created when it's first formed. I think what you're talking about would orientate the primary field, not the weak field.

	▲	skew-aberration 2 hours ago \| parent [-]
		The second field can probably be created by changing the first field while the piece is still cooling down.