Mexican 8 Reales Coins Authenticity Question

Too bad I got on so late. The 1740 is an obvious fake based on the fact that you can see where the edge details intrude onto the denticles. Look at the two segments of the lotus edge pattern between the left Mo mint mark and the rosette to the right of the mint mark. Both cause distortion of the rim (trace of dentils). On originals the edge design was added FIRST before the coin was struck in the open screw press. The reason the coins blanks were edged first is simple. When the blanks are cut out they are round. They use a cookie cutter sort of device to cut out circles of silver. These perfectly round blanks work well in the parallel two die edge mill. But once the blank is coined in the screw press it deforms - gets out of round. Like squashing a lump of putty between two flat surfaces. Once the coin is out of round it jams the edger mill and also produces an irregular edge pattern.

Knowing how dies are made and how coins are made is essential in the process of identifying forgeries.

The Spanish Colonial issues were made in a manual open sided screw press between two essentially flat dies. This would be an "open collar" strike. The silver flows freely outward at the perimeter. The collar die was not introduced in Mexico until the 1870s.

The counterfeits that are edged after creation are usually castings. The edge details are applied after the edge has been filed down to remove the traces of the mold seam and the vent and sprue. Sometimes, traces of the file marks are still visible under the edge design. Remember in most originals that the edges should not have been filed. Adjustment for weight was done by filing acrosss the surface of the blank NOT by filing the edge. Filing the edge would cause the blank to slip or pop out of the edging machine.

There are nice sketches of the machines in "Hooknecks" by Hubbard and O'Harrow. If I knew how to post a picture I could scan the pictures.

I use the term dentils or denticles interchangably since I have seen books that use both terms. I mean the small tooth like design that runs around the faces of the coin near the rim.