From Wikipedia, For silver crowns, the grade of silver adhered to the long-standing standard (established in the 12th century by Henry II) – the Sterling Silver standard of 92.5% silver and 7.5% copper. This was a harder-wearing alloy, yet it was still a rather high grade of silver. It went some way towards discouraging the practice of "clipping", though this practice was further discouraged and largely eliminated with the introduction of the milled edge seen on coins today.