1798 , 8 Reales Mexico Real Or Fake ?

i see no obvious red flags.
it's a bit light but not too much.
i own quite a few of these, and have viewed/passed on many more.

westy00

Since the coin has the mint mark of Mexico City and bears the Portrait of Carolus IIII, you should be made aware that millions of counterfeits of this type were made for the China trade between 1820 and 1930 after the supply of original coins was largely consumed (before 1820).

This type of coin was valued by the Chinese merchants at a value of 20-25% over the actual silver content because the coin was preferred by inland silk and tea producers. These farmers trusted this one coin over all other Spanish Colonial coins because of the "Fat man" with the broad hair ribbons and the Mo mintmark. Makes little sense but it is true. These counterfeits which I classify as Contemporaneously Circulating Counterfeit (CCC) varieties were made in a variety of silver alloys from 800 fine to 925 fine in England and the US. England also produced base metal copies and Sheffield plate examples as well. All types are usually CCC types regardless of alloy.

Based on the edge appearance and the overall look of the coin I would ask to have it tested with a hand-held XRF or lab XRF looking for the proper Gold trace. All Mexico City 8 Reales of this era used silver contaminated with gold. To be genuine a reading for gold must be seen on a hand-held unit of 1/10th of one percent or higher to be real. I have seen readings as high as 3.8% gold. Lab apparatus will give a more accurate look at silver and copper content, but that level of accuracy is not really needed. The lack of gold using a hand-held XRF condemns the coin as one of the CCC types but cannot tell you where or when it was made. Most of these silver CCC types are unfortunately treated by collectors and dealers as if they were genuine. They may be genuine silver but they need the gold to have been manufactured anywhere before 1890.

Density tests to detect the variations in silver content away from 903 fine would require a boxed 4-5 decimal place analytical scale to measure. Most 1/100th gram scales will not be accurate enough to be able to distinguish between 850 and 903 or 925 silver.

The surface irregularities may indicate a cast coin edged after it was made. The edge does not appear to show the same field damage visible on the obverse. The edge shot captures one of the two edge overlaps in the design (the two circles that touch). Look at the edge exactly opposite that point (180 degree rotation) to see if there is an overlap of the same length. To be genuine at any time that overlap is essential based on the physics of the apparatus used to edge the coin.

Also in this case, you have the advantage of a readymade window into the interior of the coin. The large delamination on the reverse can be tested to see what the core metal is. You could find a point within the delamination where a small scratch could answer what the core metal color is. Copper was usually used as the core metal for off metal Sheffield plate examples.