Hello, this is my first post. Firstly, I'm super happy to find this resource. I've only been enjoying this hobby for the last two years. Still much more reading, learning and collecting to go.
I recently bought this 1794 8R with what looks to be an altered mintmark. The PR assayer's initials and the year should be associated with the PTS mintmark, but instead there's an MO mintmark with longer than expected serifs surrounded by a bunch of scratches. Mass = 26.51 g, diameter = ~42mm. Not magnetic and has a nice ring. The first thing I noticed when I held this coin was that it felt thinner and a lot wider than my other Carolus III/IIII 8R's (most of them being in the region of 38mm).
Some questions: Is this a counterfeit? If not, why alter the mintmark? It's so thin and pancake-y, why?
I would highly recommend getting a copy of The Un-Real Reales if you haven't already. As a very broad summary, the author (swamperbob, who regularly posts on this forum) discusses that a significant premium existed for Mexico City mint 8 reales used in trade in China. This premium meant that people were incentivized to counterfeit or sometimes modify genuine coins to imitate Mexico City mint 8 reales. Looking at your coin it seems to be a modified genuine Potosí 8 reales. The premium varied over time, but could have been in the vicinity of a 16% (pg. 145) profit to alter the mintmark.
Yeah, that's a genuine Potosi piece that was altered. Late 1780s-early 1790s Potosi pieces are typically larger in diameter than Mexico City mint products.
threefifty's notes what swamperbob has said about these in the past, which seems to be a reasonable explanation.
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