Thanks for the quick reply.
I guess I've never seen steel that thick and be light enough to toss, nor have a seen cast iron that thin :) it does feel a bit brittle.
So you think the residue is part of the cast iron process? Nothing to worry about in terms of dodgy carcinogenic chemicals?
I've received a wok as a gift from a Chinese lady which has a silvery/grey, sort of graphite-y coating. By graphite-y I mean it's similar in colour and shine to lead from a pencil. I can't seem to remove it! The coating comes off pretty easily onto my hands and paper towels. I've tried...