100,000 year old use wear from Pedra Furada, Brazil

[Beagle]

Yep, the rate of oxidation depends on a number of factors. I sent you an email.

[AD]

Actually, I meant how long would it take to oxidize metal down to the point when it lost virtually all of its magnetic properties

Depending on where it landed and spent its time between its deposition and your recovering it, an iron artifact may have survived relatively intact for thousands of years, or it may have disintegrated after only a very few years. Oxidation (a.k.a. rust) is (surprise!) caused by oxygen, the process being enabled and accelerated by the presence of moisture.

[Minimalist]

Charlie's stuff is being eroded out of the ground. There is no way to tell how long any particular piece lay on the ground before he picked it up.

[Digit]

Sorry folks, but I still don't get it. Iron Oxide was for many years the chosen material for magnetic recording tapes!
Leave any Iron based material in one position for long enough and the Earth's magnetic field actually magnetises it. This is why metal ships are 'swung' at their anchor.
I'm obviously missing something here so hopefully sombody can put me right.

[Beagle]

Iron oxide is just rust though Digit.

[Digit]

Quite Beag, but as I pointed out it was used for many years as a magnetic recording medium. Despite being an engineer I haven't a clue whether it's magnetic or not and I haven't been able to find out.

[Minimalist]

One thing I don't get is this...well, one of many actually.

Iron Oxide is usually reddish. Charlie's "bird" seemed more gray than red, particularly when you hold it up in dim light. I saw it in April and that was a while ago but I didn't think it looked particularly 'rusty.'

[Bruce]

http://www.fullbooks.com/Getting-Gold1.html

We read no farther than the second chapter in the Bible when we find
mention of gold. There Moses speaks of "the land of Havilah, where
there is gold"; and in Genesis, chapter xxiv., we read that Abraham's
servant gave Rebekah an earring of half a shekel weight, say 5 dwt. 13
grs., and "two bracelets of ten shekels weight," or about 4 1/2 ozs.
Then throughout the Scriptures, and, indeed, in all historic writings,
we find frequent mention of the king of metals, and always it is
spoken of as a commodity highly prized.

I have sometimes thought, however, that either we are mistaken in the
weights used by the Hebrew nation in early days, or that the
arithmetic of those times was not quite "according to Cocker." We
read, I. Kings x. and xli., that Solomon in one year received no less
than six hundred and three score and six talents of gold. If a talent
of gold was, as has been assumed, 3000 shekels of 219 grains each, the
value of the golden treasure accumulated in this one year by the
Hebrew king would have been 3,646,350 pounds sterling. Considering
that the only means of "getting gold" in those days was a most
primitive mode of washing it from river sands, or a still more
difficult and laborious process of breaking the quartz from the lode
without proper tools or explosives, and then slowly grinding it by
hand labour between two stones, the amount mentioned is truly
enormous.

If we're to believe people were here 100,000 yrs. ago these rocks may have been used to mine gold. This article is still the clubs position on how rocks were formed in North America. I beleive most gold rushes were gold recovery, and possibly robbery, of the people's that have been here before. It was nothing new, Clovis collected gold too. Who did they kill that they needed 6" spear heads?

[Beagle]

Who did they kill that they needed 6" spear heads?

Very interesting post Bruce. But I think the answer to this question is the Wooley Mammoth.

[Digit]

Interesting point there Min. Cast Iron is Iron and Carbon, now the heating process for the Iron can, under the right circumstances remove any impurities and pure Iron does not 'rust'.
If it is a gray color then possibly the covering is Iron Sulphide, Sulphur is one of the more common impuries it Iron and weakens it, so now a days it is removed, usually by blasting air through the molten mix which burns off the Sulphur.
The painting of rusty Iron based materilas with Sulphuric acid converts the Iron Oxide to Iron Sulphide, which is rust resistant.

[Beagle]

In this case, the "bird" does not seem to be of a modern mixture. iirc it was said to be a rather pure cast iron. I'll check and follow up on that. That would seem to indicate that it might be older.

[Rokcet Scientist]

Who did they kill that they needed 6" spear heads?

Many 'big questions' have a tendency to sound ominous and suggest dramatic answers. In practice the answers are usually very simple and down to earth.

[Minimalist]

now the heating process for the Iron can, under the right circumstances remove any impurities and pure Iron does not 'rust'.

Yeah, but if that were the case it would prove Charlie's point anyway. When did Europeans reach that level of technology with regard to iron?

The whole point is that if that thing is forged metal, (and I've seen comments from university people which seem to say that it is) and it was not forged by Europeans then the book gets thrown out the window anyway.

Then again, if you have that technology why make an ornamental bird instead of a breech-loading cannon?

[Beagle]

Yeah. Min, I looked at those comments again and the bird seems to be just a cast iron mold, and possibly the mold was the shell of a marine animal.

I'm not sure where Charlie goes from here, but the whole thing is really fascinating.

[Digit]

Exactly Min, that's why I mentioned it. In the quantities I am familiar with that level of tech was not reached until, (I think) the 19C.
There is in, I believe India, a famous Iron pillar that is many hundeds of years old that has remained rust free and is supposed to be pure Iron.