World of Coins

Coins of long traditions => Cash type coins => Topic started by: bgriff99 on February 10, 2019, 08:21:50 AM

Title: Japanese bita-sen found in central Vietnam
Post by: bgriff99 on February 10, 2019, 08:21:50 AM
Some bita-sen, exported from Japan circa 1600-50.    Metal content tends to have considerable amounts of iron and arsenic.    Strangely, they can combine, if the arsenic exceeds the iron level, into a non-magnetic compound.    Such a coin can have above 12% iron and be nonmagnetic, while one with 1% iron and no arsenic will be magnetic.
Title: Re: Japanese bita-sen found in central Vietnam
Post by: THCoins on February 10, 2019, 11:52:24 AM
Beautiful patinas on these specimen, and such a range of colors !
I guess that's both the result of metal composition and the surrounding in which it was preserved.
Interesting observation about the magnetism. Since i standard have a small strong magnet on my desk i have been surprized by how many coins which i thought of as billon or bronze turn out to be magnetic. But that's in north-Indian medieval coinage. Here the presence of magnetic coins seems to correlate mostly with times of political crisis.