You have it partially right, but it is a light film of oxidized oil. The oil then picks up bits of microscopic metal. However that type of glaze can actually be cleaned out or at least prevented with high detergent oil. The glaze that cannot be removed is caused by high surface temps and bits of microscopic metal actually fuse to the surface.

Not high detergent oil is a no no in aircraft engines.

http://www.prime-mover.com/Engines/L...Operation.html