This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
If the luster of coins fresh from the mint is to be preserved, they must be immediately placed so as to be protected against contact with the hands. A good holder that will display both sides of a coin can be made of two pieces of glass, BB, between which is placed a cardboard cut as shown at A. The cardboard should be about the same thickness as the coins. The glass may be framed by using strips of wood rabbeted to receive the edges of both pieces; or their edges may be bound with passe-partout tape. Even when a frame is used, it is best to bind the edges as this will prevent tarnish from the air. Old negative glass is suitable for making the holder. - Contributed by R. B. Cole, New Haven, Conn.
Ill: Two Pieces of Glass Inclosing between Them Coins of the Same Size and Thickness