8 Reales 1793 Fm Sniff Test

Sometimes debased silver alloys will create severe cases of copper leaching at the surface as we see these green? specs throughout - with debased silver alloy specimens copper replaces silver in the alloy composition. As Bob has seen in the preparation of the CC8R book we have seen Ag levels from ~20-85%. Most high copper billon (Cu/Ag) alloys are unstable creating the more oxidized material coming to the surface - in this case - copper. This appears to be the case from these photos as these specs appear GREEN (CuO). Why are New Orleans Morgans so colorful on just one side?
I am currently looking into the Wartime Jefferson nickels as an example of this occurance with Mike Diamond of Coin World. Why was Mn put into this alloy of Cu/Ag? Maybe too much to hinder this process and soften the overall alloy - nothing laminates more severely than a 20thC WWII Jefferson nickel for 20thC type U.S. type coin. What is actaully causing the lamination in the Jeff Nickels? The metallurgy here is similar if these indeed are copper inclusions at the surface of this Class 2 CC8R (China - Debased Ag alloy). As Bob alluded to the earleir Class 2's had higher Cu levels earlier (i.e., post 1830) and as testing got better in this counterfeit market Ag levels rose to near regal like 75-85% Ag for this class of contemporary with time based on our testing.

John Lorenzo
United States

At 25.9 grams - in the condition pictured - I get a bit uncomfortable calling any coin genuine unless I can see a reason for metal loss.

At 29-30 mm in diameter - the coin CAN NOT be real. Original 8Rs are around 37 or 38mm with some as large as 40mm but NONE under 35mm even the cut down and re-edged. So here I presume an error has been made and you meant between 39 and 40mm. This is large for Mexico City but not impossible.

I see a very small area of corrosion which is not large enough to account for 1.9 grams of missing metal. So with weight and the large diameter I am somewhat suspicious.

I would suggest you try SG testing but make sure you use a reliable scale that is absolutely accurate to 0.01 grams or better.

The mouth on the King is odd (straight line) and that could point to a very well made counterfeit or an altered coin.

Authentication in this series is only just beginning to be turned into an accurate science.

Official prescribed weight was 27.07g, and it didn't vary much in these years at Mexico.

The whole piece is sort of microscopically rough (has a flat/matte look, if I'm deciphering the scans correctly)... then there's that more obvious roughness/porosity that culminates in notable surface loss to corrosion around the date and the nose/mouth (Bob, I wonder if that's not what's making his grin look odd...). Overall, I think there's enough environmental impact there to argue for a legit 1.1 gram loss.

Bob, if nothing else... if it was a bad-enough cast to leave such (under some circumstances) "obvious" casting signature (all that raised roughness), I would think the weight would be lower (or the "coin" would be too thick).