Larger 3.5" disks are typically metal, smaller 2.5" disks are usually ceramic. Not sure on coatings on ease of cutting. They do make good mirrors though!I didn't want to derail XM360's RGB review and I noticed Arcticdude used some disc's from a hard drive for front surface meters.
How good are they and can they be cut easily?
I scored a few drives when I busted up a security module and it's just a thought.
Are these disc's also platinum plated?