reading these messages has got me confused, i had made my list then thought i would check to see if anyone had posted a list.
copper nickel
compact disc
iceland spar
brass plate
Thanks to all the above! Having posted this question in the first place I'm glad to see others are as undecided as I am! I was going to go with Brass Plate and Copper Nickel (ex Chambers) but will have to give it more thought!