Technical Questions about struck metal

JohnHarper

Many years ago I used a product that would bring out the date on "dateless" Buffalo Nickels. I assume it included acid. My question, what is it about the metal that makes this happen? When a coin is struck, is the metal compressed more in some areas than in others? Does the metal become harder in some areas than in others?

Is this also true for dies? When design elements are punched into the dies, if there a difference in compression or hardness across the die? Who is the authority on this topic that can discuss this with me?

coindeuce

"When a coin is struck, is the metal compressed more in some areas than in others? Does the metal become harder in some areas than in others?"

Generally speaking, the answer is yes and yes. Without giving a full definition of Young's Modulus this would be somewhat difficult to explain here. The hardness of the relief design of the date on a Indian Head nickel extends below the plane of the surrounding field, much in the same way that the serial number stamped incuse on a firearm hardens the metal below the depth of those number punches, and makes it possible in some instances to recover a serial number has been filed smooth by applying acid to the frame of the firearm.
Recent research has proven that Mint workers even used acid etching for the purpose of modifying & repairing working dies. This was borne out especially in the area of Morgan and Peace dollar die variety study.