I went for a walk a couple of days ago and I found an object – ok, an old rusty washer – on the footpath beside some old mine tailings, possibly brought to the surface by the recent rain.

I thought that there was an outside chance it might be a very corroded Chinese cash coin, but no, even though it’s roughly the right size, weight and thickness it’s clearly just an old rusty washer.

Why can I be so definite without a detailed examination? Well one of the distinguishing features of cash coins is that the hole in the coin is square

and the washer has an almost perfectly circular hole …