This short note presents the background to the coinage trials held at Whitehall on 8 May 1651 and the details of the grained edges that were specified as part of the trials.
The sequence of events can be found in the book; “The Answer of the Corporation of Moniers in the Mint“, published in 1653, which is a compilation of several documents, letters and pamphlets. These trials heralded the introduction of grained and lettered edges to the silver and gold coins to ward against counterfeiting and clipping.
The grained edges of the trial pieces produced by David Ramage and Peter Blondeau are looked at in detail, along with the grained edges that can be found on later ‘milled’ coins. Features of the grained edges confirm that the Blondeau patterns and later pieces were edged using a Castaing type machine, the design and operation of which is described.
BNS Research Blog 
I found this article both interesting and informative. The photos and drawings were excellent. Thank you.