1781 Mexico 8 Reales - Not Sure If It Is Real?

I don't like the coin. Gut reaction is C/F but you got some nice chops. What's it weigh? There is an expert on 8 Reales on Coin Community. Perhaps he will see your post.

It's a residue of some sort. I picked some out with a toothpick. It's silver colored inside of the chop mark.

It's also, just under 40mm and in "medal" alignment.

Here is a better shot of what I think you are talking about, plus a shot of the rim 180 degrees away.

Ok, my scale says between 26.6g and 26.7g the multiple times I weighed it. I assuming that is good, right? Also, it's not magnetic, and rings like silver. I'm not sure about specific gravity, I don't think my scale is accurate enough to take those measurements. Assuming it is genuine, what is the approximate value of this coin?

Nice coin, it has some history behind it. I vote genuine. I am not sure I would agree that there is a filled hole, that may just be extreme damage from back to back chops, the reverse first destroying the assayer initial and the following really deep obverse one just wiping out any semblance of design on the reverse when it pushed through. It would be easier to determine with coin in hand so looks like the original poster will need to do some investigating.
Great coins to collect, I hope this one is just the start of a serious addiction to 8's

matttheriley A scale accurate to only the nearest 1/10th gram would not be accurate enough for specific gravity.

However, if you have a micrometer set you might do best with a volume approximation. Measure the thickness of the coin at a minimum of two high points and two field locations. Average the 4 readings and that is the thickness. I have a metric micrometer but inches is fine - you just need to remember to convert. The density is weight divided by volume.

So use weight in grams and divide that by volume in cubic centimeters (cu cm).

On my desk I have an 1839 Durango 8R that arrived today. I decided to do a crude approximation of SG and then a slightly better one to see how it came out.

First example; I used a wooden school ruler and cheapie scale ($9.99) that was accurate to 1/10th gram.

The coin looks like it is 38 mm. My eye could NOT DETECT the fact the coin was out of round as I learned later.

Thickness was between 2 1/2 and 2 3/4 mm at the rim (average 2.625). To my eye the rim looked even with the high points of the coin. Having done measured approximations before I knew the field should be about 1/2 mm thinner. So I estimated the thin point by reducing the rim average of 2.625 by 0.5. The average of thick (2.625) and thin (2.125) was 2.375mm.

The area of the coin calculated to 11.34 square cm.

Volume 11.34 x 0.2625 = 2.69 cubic cm

SG = 27 /2.69 = 10.037 which rounds to 10

Second test: Using a micrometer set metric (flea market $35), the diameter measures 38.50mm average of two readings taken at 90 degrees. In this case the coin is very close to round but not quite round. You can take readings at every compass point if the coin is badly out of round. (Hint: Stick to the compass points do not just go for smallest and largest diameter. Also make sure the math ends up in a sensible average diameter. I often hit the wrong key when entering numbers so double check.)

The same coin is variable in thickness between 2.224 and 2.818 mm. The 4 readings I took average 2.2516 mm. That would round to 2.25mm (you should not use more decimal places that the least precise instrument - in your case round to 1 place but in my example I can round to 2 places I use a 1/100 gram scale - small fairly cheap digital scale ($ 99.).

Area of the coin is (pi;)Pi x radius squared. Note: I just re-read the post and the Greek letter Pi translated to # 960;) when I posted it - sorry for that.

Area = 3.14159.. x (19.25mm x 19.25 mm) = 1164.16 square mm

Volume of a disc = surface area x thickness

Volume = 1164.16 x 2.2516 = 2621.2226 cubic (cu) mm

Convert cu mm to cu cm = 2621.226 / 1000 = 2.621 cu cm

Weight 27.01 grams

SG = weight / volume or 27.01 / 2.621 = 10.3052

This SG is accurate to one decimal place or 10.3 (based on significant figures).
That compares well to the wooden ruler test 10.037.

Specific gravity of 0.903 fine silver is 10.31.

Conclusion the coin is silver and possibly genuine.

You will be rounding to the nearest full digit but you should NEVER get a 9 reading. Good silver 903 fine will always yield 10 using this method.

Hi Swamperbob,

That is excellent information. Thanks!