Magnetic weapons

[Rivkin]

Again - magnetic properties of a macroscopic iron is a tremendously complex problem, that can be approach with numerics.

I'm not a specialist (so I wish to be corrected by ones), but:

Local magnetic structure depends on the crystalline lattice (unobtainable in normal conditions "diamond" iron for example is even anti-ferromagnetic), including stress, grain size etc. There are dozens (!) of phases that correspond to basically chemically similar steels that have different crystalline structure (and btw hardening is the way to obtain a metastable crystalline structure).
These lectures notes can be of help:
http://neon.mems.cmu.edu/laughlin/pdf/252.pdf
btw austenite is paramagnetic.
It will greatly depends on local chemical decomposition.
It's going to greatly depend on how uniform and fast the cooling is (uniform cooling leads to permanent magnetization alongside the local magnetic fields)
In general there are some companies who measure conductivity and magnetic permeability in order to undestand how uniform their steel is. I don't want to refer to non-publicly available papers, so:
http://doc.tms.org/ezMerchant/prodtm...df?OpenElement

Now to the question "what happens to a sword":
1. Swords are intrinsicly anisotropic due to their shape.
2. They are usually completely non-uniform in their magnetic properties due to nonuniformities of steel they are made off, and nonuniform cooling (first of all - nonuniform quenching).

Before I've the patterns of the dagger that were shown here I believed that such patterns can be produced by a weird external field. Now I think that because they are so damn non-uniform, and most of the dagger is not magnetized at all, the structure of this dagger should be tremendously non-uniform by itself, and I believe that conductance or X-Ray tests can prove that.

Now to what happens to swords when they lie in Earth. I thought about who would've been interested in this, and realzied that mine detector peoples are.
And indeed one can read a very interesting pamphlet over here:
http://neon.mems.cmu.edu/laughlin/pdf/252.pdf]

one should keep in mind that they are interested in a dipole moment i.e. the magnetic field procuded by objects very far away from the object itself, so it's much more uniform and depends on Earth's magnetic field in a much more direct way (since those guys quetly cool down underground), but we are interested in a local magnetization - quadrupole and up moments, that create these beautiful patterns.

[Ann Feuerbach]

Thanks. Lots of food for thought!

[Rivkin]

You are welcome.

Btw, the thing I always wondered about archaeomagnetism people - do you take in mind only the total magnetization and connect it to the strength of the Earth's magnetic field at the time of making of the object, or you actually use oomf/rkmag to see how the object with such chemistry and shape would react to the applied magnetic field of such strength ?

[Jim McDougall]

Hello Ann,
I would like to also welcome you to our forum, and to say what an honor it is to have you join us. I have had your outstanding work "Crucible Damascus Steel"for some time now, and it is brilliantly written!
For someone such as myself who is fascinated with history, yet lost with the complexities of physics, science and technology, it is an entirely readable and well crafted blend of history with well explained technical details.

This thread, as well as that of meteoric iron, have really become high profile and I am delighted that Jens posted them, as the knowledge and discussion has become irresistable! Aside from your extremely interesting article, most discussions on these topics can be quite dry to most of us in the lay world....but this thread keeps getting better, and your joining us is outstanding!

All the best,
Jim

[Ann Feuerbach]

Thank you Jim for your kind praise. Believe it or not, I was condemed by my PHD supervisor for not writing "academic" enough. I think that means big words and complicated sentence structures! However, my Russian friends said they like it because they can actually read/translate it easily. I always thought that the was the point of academic writing. Obviously I am not of the elitest academic type. I have so much more to add for the book that could not be put in the PhD
As to archaeomagnetism testing. I believe that the process involves carefully measuring the angle of declination as well as intensity and direction before it is removed from the ground, and then again in a special chamber to eliminate outside forces. I do not recall off hand how much the objects make up is involved.

[Mare Rosu]

OK ALL
I said I was winding down on my part of this thread started by JENS, and after reading
Ann and RIVKIN input on this magnetic stuff I should have stopped last week! Do all you follow their exchange? Man that is some heavy stuff. Anyway I said I would do as FEARN suggested and acquire a magnetic knife holder and zap a carbon blade.
I used a Case butcher knife, as was in contact with the magnetic holder for approximately five minutes, the pictures show that the blade did take magnetic profile with three pols.
I also took a picture of the Mysore dagger with four compasses on the blade to show you that it has the four changes all at the same time.
Gene

[Jim McDougall]

Hi Ann,
That is exactly what is great! You are able to discuss material that is typically pretty involved and technical and integrate fascinating historical data, which makes it possible to understand
The original course of this thread was to try to discover how extensively lodestone was involved in the wootz in blades. In some of the material we discovered it seems that it inadvertantly occurred in the raw material from Hyderabad, which remained in certain janbiyya blades found in Arabia.

The ensuing discussion here has been fascinating, and I think I've learned more than in any science class I ever took! ( as far as I can remember...the little red schoolhouse ya know!!

Gene,
You better not bail out on us here!!! You have been doing an incredible job of scientific experimentation, I think the first of this type I can recall. What you are doing presents some excellent hands on perspective for some of the somewhat complex ideas that have come up. Thank you for following through on this !!! Outstanding work!

All the best,
Jim