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Can anyone tell me for sure what material the Western Digital HD are made? They shine like mirrors and seems steel. Answered

I dismantled an old WD HD 2.5 Gb to use the neodymium magnet, and to my surprise I found that instead of a disc, it had three, stacked. I was also surprised for its mirror finish, I expected a dark brown surface, like floppies. Can anyone tell me for sure what material they are made the discs? Aluminum is not, must be steel, but it must be stainless steel or be well covered, because they shine like mirrors.  


The surface of the platters is made of a different material than the bulk of the platter.  According to the Wiki article linked below, the surface coating is a cobalt alloy, while the remaining bulk structure of the platter, the substrate is made of "aluminum or glass and ceramic".


Be careful if you're dismantling 2.5" laptop drives. I bent a platter of one of these once to get an idea of what sort of 'metal' it was made of and it turned out to be coated glass.
It shattered and peppered me with a billion razor-sharp shards. 
I escaped with just a cut finger but it could have been a lot, lot worse if I hadn't been wearing glasses at the time.

i aways thought that there was a very thin layer of patinum on them

Its a very complex material. Its NOT a simple iron oxide compound anymore.