The SF Mint on average can produce about 200,000 collectible proof coins per day. More than 20.1 million were struck there last year alone.

In the mechanics, a blank slides into position flat side down so it can get squeezed between two vertically placed dies. These dies bear negative images of the heads and tails side of a coin. When the press applies some 90 tons of pressure between them, the blank flows like putty and accepts their designs. The blank doesn't flatten like a penny in a souvenir machine as a surrounding collar restrains its expansion. That collar also creates a coin's reeded edge or imparts the edge-incused lettering on Native American $1 Coins and Presidential $1 Coins.

In a large L-shaped area that San Francisco Mint employees call the Coining Press Room, there are nearly 20 presses lined up against walls. But before blanks get to them, they first receive some special attention. Though they have already been through the Treatment Room, the blanks are manually washed, dried and buffed. That's quite an undertaking with the millions of proofs minted each year.

To read the complete article, see:U.S. Mint at San Francisco, Coining Press Room(www.coinnews.net/2013/04/17/u-s-mint-at-san-francisco-coining-press-room/)

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