An antique, automatic watch movement, from the Elgin Watch Company, has a coating of resin on one side only.  The other side with the balance disk is still free to move and spin along the central axis.  If the watch worked, every time the disk makes a complete spin, it would turn a single tooth of a gear, which would then turn the spring, which would wind the watch automatically.  The gold-colored metal of the watch movement goes well with the 20K gold plated chain, of which it is hung from.