On or around Wed, 18 Aug 2004 17:21:09 +0100, rads enlightened us thusly:
see other post - copper's different. Play with a piece is best. If you bend it backwards and forwards, it rapidly becomes stiffer (ooer) and then breaks.
however, anneal it, by heating it to bright red and quenching, and it becomes very soft.
and BTW, the modern collapsible washers can't be done like that, you need nice solid copper ones.
I've got into the habit of making me own, in fact. Cut 'em out of a spare piece of copper pipe, suitably opened up and flattened.