Assayer

In the mints of the early modern period, the assayer occupied a position of considerable importance and, in some jurisdictions, considerable legal responsibility. The assayer’s function was to test the metal used in coin production – verifying that blanks met the required standard of fineness before striking and that finished coins conformed to the specifications laid down by the issuing authority.
The assayer’s mark, typically one or two initials punched into the coin die, appears on a wide range of European and colonial coinage from the fifteenth through the nineteenth centuries. On Spanish colonial silver – the famous pieces of eight and their fractions struck at mints in Mexico, Potosí, Lima, and elsewhere – the assayer’s initials are among the primary means of attribution and dating, since the large authorization date on the coin often tells only part of the story. Knowing which assayer held office at a given mint during a given period allows the specialist to date and attribute cob coinage and early milled pieces with considerable precision.
The legal weight of the assayer’s responsibility varied by time and place. In some mints, assayers were personally liable for short weight or substandard coins that passed through their hands, and cases are recorded of assayers facing severe penalties – financial ruin, imprisonment, or worse – when systematic fraud was discovered. This accountability was the point: the assayer’s mark was not merely a bureaucratic notation but a guarantee, and the individual behind it was expected to stand behind his work.
For collectors of Spanish colonial coinage in particular, the assayer’s mark is one of the most important details on the coin and a primary driver of relative rarity and value among otherwise similar pieces.