Coin Study
Silver Spanish 8 Reale Coin 1766

This study investigates a Spanish colonial Pillar Dollar or 8 reales. These coins have long been faked and in-period counterfeits were also made. The coin's weight and diameter are correct at 26.89 grams and 38.5 millimeters. The coin is clearly a struck coin with typical flow mark details around the date and letters, particularly near VTRA. The coin's wear and tear looks natural. 

But the coin holds at least one mystery,  excess metal on the pillar side between the letters E and V of QUE -- VNUM. Further, the excess metal appears to have occurred during the striking process when the coin was made, not added later and not part of a casting process. The details of the excess metal are described below. In addition to whether the coin is authentic or not, the question is what possible process could have formed the excess metal with its peculiar shape?

Coin (click zoom to enlarge)

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The rims have the typical repeated flower pedal design of the period. The complete pattern is made of two slightly misaligned half patterns each covering half of the rim area. The alignment mismatch can be seen in the bottom image where red and blue markers mark the individual design units, which are not aligned with respect to each other. The direction of the petal units is the same on both halves of the rim.

Excess metal

The excess metal runs from the letter Q through the letter V and had several very curious features.

The apparent hole between E and V is a void in the excess metal and does not continue into the planchet.
The upper edge of the excess metal is finely serrated forming a perfect inverse of the denticles along the rim.
The upper edge appears to have been shaped by a stricking process.
The thickness increases slowly from the sides to the center where it is even with the tops of the letters and the rim.
There are clear outlines around the letters which again show evidence of striking.


Magnified again

Other Examples

A search of the internet for other 8 reales from the Mexico City mint dated 1766 yielded interesting results. Out of about 10 or 15 higher resolution images found, two other coins show signs of the same anomaly. In the first example, the feature appears to be in the early stages of developemnt and in the second example the feature is more developed like in the coin under study. In all three examples, the features share common detail suggesting they are from the same die.