I get a lot of feedback from numismatists who acquire a copy of my Encyclopedia of Coin and Medal Technology. These experts amplify - or even correct - statements found in an entry in which they have extensive or expert knowledge. One of these arrived this week from early American coinage expert Craig Sholley.

Craig mentioned a term I was unaware of; Hydrogen Embrittlement and also mentioned Pitting Corrosion.

Hydrogen Embrittlement
He stated the hydrogen embrittlement was fairly common on US proof dies from 1836 to early 1900s. This was caused by the use of acid etch to create the frosting or satin surface on proof dies. This anomaly is not observed on coins prior to 1836 because of the small number of proofs struck.

I would like to add the year 1836 was an important date because coinage was influenced after that year by technologies Franklin Peale learned at European Mints and applied these practices for coinage at the Philadelphia Mint. Apparently Peale didn't learn how to prevent this or Mint officials there didn't inform him.

Pitting Corrosion
Pitting corrosion, Craig goes on to say, occurred on dies as early as the 1800s and up thru the late 1880s.

Regarding the Encyclopedia, Chester Sullivan writes:

For more information on Dick's book, see:
NEW BOOK: ENCYCLOPEDIA OF COIN AND MEDAL TECHNOLOGY (www.coinbooks.org/esylum_v19n17a05.html)