How does a planchet become a Proof coin?

A Coin World archived video recently shared on our Facebook page shows you one step in the process. 

During a 2013 trip to the West Point Mint, Senior Editor Paul Gilkes captured video of raw silver blanks for the 2013 American Eagle West Point Two-Coin Silver Set being spun with steel media and chemical solution in a Spaleck Finish machine to brighten the finish of the blanks, preparing them to be struck with a Proof surface.

Have a look.