Not all magnetite can become lodestone, it takes a special crystal structure, see what Dr. Peter Wasilewski, of NASA's Goddard Space Flight Centre, writes here http://www.phy6.org/earthmag/lodeston.htm
this will answer some of the questions asked.
Fearn, I am nor a specialist on this, but I would think, that if you fold a blade many times, it will loose magnetism. I agree with you, I also think the magnetism on blades was made later Ė but why?
If we believe in what Dr. Peter Wasilewski writes, the lightening together with a good portion of superstition would lead them to believe that the Gods had made this metal.
I donít know if lodestone was ever used for weapons, maybe it was too difficult to get the iron out of the stone, or maybe the percentage of iron was too small, I donít know Ė but one thing it could do, and that was making other iron weapons magnetic. If they believed that the Gods gave them this stone, they would also believe in, that using this stone to magnetize a blade would give the user more power.
Nechesh, I know you did not advocating for magnetizing blades. I clean my blade and etch them, but I donít magnetise them. The reason for this is that I donít know if the blade was magnetised from the start, that is why I leave it be.
Rivkin, it seems as if Dr. Peter Wasilewski does not agree with you about the magnetic felt of the earth when it comes to lodestone, maybe the magnetic felt could influence ancient pottery, I donít know, and I donít know the reason for this.
I think you are right, that if any magnetism would be recovered in a blade after heating, it must cooled very slowly Ė just like the Indians did with wootz.
The defects in crystalline structures, what other metal the iron was mixed with, even in very small doses must have been a problem for the smiths, as this would have affected the way the iron should be treated. It seems to me, that wootz from one ore might have needed a slightly different treatment than wootz from another ore, according to how the iron was mixed. But I never saw anywhere that the wootz ores were magnetic, only the lodestone.
Robert, on the first link I gave, it somewhere say, that if you take a big nail which is not magnetised and hammer on one end for 50 times, the nail is magnetic Ė if you turn the nail and do the same on the other en of the nail, you will change the poles.
Jim, I think a crude compass was made much earlier than about 11th century AD, try to read this:
For many years magnetism was just a curious natural phenomenon and its only use was in navigation as what we now refer to as the mariner's compass and which was probably first developed by the Chinese some 4500 years ago. The earliest mariner's compass comprised a splinter of loadstone carefully floated on the surface tension of water.
You can find the whole text here http://www.newi.ac.uk/BUCKLEYC/magnet.htm
if you are surprised when reading this, I understand you Ė I was surprised too.
Does anyone know if lodestone alone, or in combination with iron/wootz was used for making weapon?
Interesting questions you ask Ė but you must remember that I am not an expert Ė I try to learn as fast as you ask the questions.
yannis, interesting what you write to Jim, try to have a look on the link I gave him.
Yes, filing on a blade can make it magnetic, but you would have to file in the same direction the whole time - not back and forth, and I think it would be an advantage if the file was magnetic. I doubt however if it would make a kard blade as magnetic as the one you have, but I don't know it.