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Mystical Magnetic Fields: Newsletter Challenge (October 2017)

Posted September 30, 2017 5:01 PM

This month's Challenge Question: Specs & Techs from GlobalSpec:

As you know, the direction of the Earth’s magnetic field changes with time, as does “North” on a compass. Some researchers have used old paintings, such the murals in the old Vatican Library (Bibliotheca Apostolica Vaticana), or ancient clay kilns to find compass directions for specific times in the past. How is this possible?

And the answer is:

The clay in the walls of ancient kilns contains the iron oxide magnets magnetite and hematite. These materials contain individual grains in which there are “ domains”—regions in which the magnetic fields of the material are uniform.

When the clay is heated to hundreds of degrees Celsius as the kiln is used, the domains already aligned with the Earth’s field increase in size while the others shrink. When the kiln cools after using the arrangement of the domains—and also the magnetic field of the clay—is retained. This is a well-known phenomenon called thermoremanent magnetism (TRM).

Many mural paintings—including the murals of the Vatican Library—contain hematite suspended in the liquid pigment of the paint. When the pigment is applied to the wall each hematite grain rotates in the liquid until it is aligned with the Earth’s magnetic field. When the paint dries the orientation of the grains is locked in place, and therefore indicate the direction of the Earth’s magnetic field at the time of the painting.

Researchers have several methods to determine the orientation of the grains in a kiln or in the mural at any time.

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#1

Re: Mystical Magnetic Fields: Newsletter Challenge (October 2017)

09/30/2017 5:39 PM

Ceramic Pottery Reveals an Ancient Geomagnetic Field Spike

https://www.livescience.com/57868-earth-magnetic-field-spike-ancient-times.html

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#2
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Re: Mystical Magnetic Fields: Newsletter Challenge (October 2017)

09/30/2017 6:13 PM

Cores from ancient lava flows ALSO contain magnetic polarizations that can be read to find where the magnetic north pole was when the lava was cooling.

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Re: Mystical Magnetic Fields: Newsletter Challenge (October 2017)

09/30/2017 8:34 PM

Yeah, the mid-Atlantic ridge is a huge magnetic "tape recorder", recording the geomagnetic field at the time that the lava solidifies.

https://www.geolsoc.org.uk/Plate-Tectonics/Chap3-Plate-Margins/Divergent/Mid-Atlantic-Ridge

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Re: Mystical Magnetic Fields: Newsletter Challenge (October 2017)

10/01/2017 11:07 PM

I understand, it's a pretty consistent interval.

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Re: Mystical Magnetic Fields: Newsletter Challenge (October 2017)

10/09/2017 8:27 AM

You are in the right track

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#5

Re: Mystical Magnetic Fields: Newsletter Challenge (October 2017)

10/01/2017 11:19 PM

I believe the 'pole polarity shift' occurs roughly every 55,000 years and we know what we call the North pole wanders around a lot in between times also we are due or slightly overdue at the present time.

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#6

Re: Mystical Magnetic Fields: Newsletter Challenge (October 2017)

10/01/2017 11:27 PM

Regarding old murals (or frescoes), any magnetic particles in the paint/plaster will align themselves with the Earth's magnetic field at the time they dry/solidify. As long as the art items remain in their original positions (as murals and frescoes normally do), careful analysis can determine the direction of the magnetic field at the time the art was created.

The above would require knowledge of the time period when the art was originally created. Theoretically, the reverse of this could be used to verify the authenticity of ancient art work.

(To Admin: Thanks for changing the answer time to one week!)

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Re: Mystical Magnetic Fields: Newsletter Challenge (October 2017)

10/03/2017 12:28 PM

clay kilns and also old murals contain some magnetic iron oxide pigments, and the domains were free to move when the medium was in a fluid-plastic state, then were soon locked into their positions.

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Re: Mystical Magnetic Fields: Newsletter Challenge (October 2017)

10/09/2017 9:35 AM

FYI, the answer is now posted.

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Re: Mystical Magnetic Fields: Newsletter Challenge (October 2017)

10/09/2017 10:45 AM

Thanks for pointing that out! I was expecting the answer to appear in a post, not back at the top...

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Re: Mystical Magnetic Fields: Newsletter Challenge (October 2017)

10/09/2017 11:14 AM

Is it so? I wonder why when we still have 20 more days to go to reach the end of the month.

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Re: Mystical Magnetic Fields: Newsletter Challenge (October 2017)

10/09/2017 11:30 AM

Partly because I suggested that a month is too long to wait (Few people have an attention span that long), and partly because the question has essentially been answered, so why put it off?

With this one, since Hannes pointed out that the answer had been posted, I finally realized why I rarely saw the answers: Since the answer was not in a separate post, I never received an email indicating that a challenge had been answered, or else never thought to go back up to the beginning to see it.

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Re: Mystical Magnetic Fields: Newsletter Challenge (October 2017)

10/10/2017 11:59 AM

You could have given me a good answer, now couldn't you....

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