Mexico 8 Reales 1838 Zs Overweight - 27.6g

to the Community!

Swamperbob:
I can't believe you actually reply! I am a big fan and own your book.
I also tested the coin on magnetic slide. It is certainly silver. However, this coin slides faster than other 8 reales I have and suggest the alloy contains more impurity(?) I am taking the coin to a local refinery who has a portable XRF analyzer. I will keep you updated.

Swamperbob:

I went to a refinery store to have my coin checked today. It is not a handheld XRF but mounted on a station with a metal cover.
It turned out this coin doesn't contain any gold. For the reference, I also checked 2 Mexico 8 reales I brought with me. The first one is dated 1818 and the second one is from 1771. They both contains ~1% and ~2% of gold.
Does it mean this coin is a counterfeit made after 1850?
I did check SG. It is 10.3g/cm^3.


1838 Mexico 8 reales

1818 Mexico 8 reales

1771 Mexico 8 reales

I tried to post an answer here which keeps getting stopped.




I will try again.

The coin can not be genuine.

All Zacatecas coins contain gold in 1838. This is supported by the results of recent test borings by the current owner that indicate an average of 1 part gold to 100 parts silver in remaining ores.

Your results do not indicate NO GOLD but an upper limit of NO MORE THAN 100 ppm. nd means NO Determination is possible. There MUST be a gold reading

Also the test shows lead higher than expected for Zs. 1950 ppm is simply too high.

The coin may have been made in the UK since their silver comes from argentiferous lead ores.

The wear on your coin looks authentic and there is a notch near the C in REPUBLICA possibly indicating it was tested. The dark spot right of the eagle's wing could be an acid test. This reduces the possibility of a recently made Numismatic forgery.

So when would a 90% silver counterfeit made for circulation make sense? In 1893 world silver prices fell to 30 cents an ounce. At this point in time it would make financial sense to copy any world silver coin that retained a fiat value above silver content. (A good example are Spanish 5 Pesetas that were counterfeited for circulation.) In 1803 I believe the Philippines still used Mexican 8Rs and used them at the old face value.

So an English counterfeiter may have targeted an 1838Zs coin as an ideal target for forgery.

This is the first find that may confirm a made for circulation silver Cap and Ray 8R. Great find.

Any questions on the XRF results just ask.

hjian I am not a fan of the slide because it does not produce actual scientific data. It is a somewhat subject instrument that displays relative response to magnetitic fields.

I prefer things like weight, density and XRF tests for determining authenticity.

If you ever want to part with this one please let me know. Meanwhile I will begin searching for a die match to it.

My address is
Swamperbob Associates
Po Box 435
Hope Mills, NC 28348

I would love to investigate it.

Swamperbob:
Ok. I will ship it next week. Don't worry about the price. It is fun to get the bottom of this. We can discuss it offline.

Hello Henry

You ask if I have looked at your coin?

The answer is yes, YES, YES and YES. I could add several more yeses. I look at it and put it aside. Then I look at it again and put it aside again. Looking each time for something new that I might have missed.

This coin is an enigma. I have run every test I normally run two or three times and confirmed all my work and I come up with the answer that the coin must be COUNTERFEIT (not made at Zacatecas in 1838) but I can find almost NOTHING that confirms that fact visually. It is a result that depends on the XRF tests.

Before I comment on the one very small visual issue that I only recognized this week after nearly 20 hours of looking, I can see I need to clear up one question about methodology where our test results did not match exactly.

How did you do the SG check that yielded 10.3 g/cc? Did you use apparent weight loss by water displacement? It appears you used a 1/100th gram scale from the result whish is displayed to 1 decimal place. That could account for the slight deviation in results that I arrived at when checking your work. When I round to two significant decimals (the best you can get with a 1/1000th scale) I get 10.39 g/cc which is off the mark and above standard 10.31 g/cc. Repeated tests on different days (I presume at different atmospheric pressures) yielded a range from a low of 10.38 to a high of 10.40 g/cc. I consider those three results to be a good check.

To be sure I have the following questions so that I can explain the deviation to myself.

1. Did you use distilled water at room temperature?
2. Did you boil the water first to remove gasses before bringing it to room temp? Did you chill the water and coin to 40 Degrees F?
3. Did you check for any tiny air bubbles on the coin? Before and after checking the weight? Did you add an emulsifier to the water to break surface tension?
4. Did you correct for temperature of the room? I keep my lab area at 70 degrees F so water has a weight of 0.998g/cc. Water is 1.000 g/cc at about 40 degrees F or 4 degrees C which is too cool for me.
5. Did you correct for elevation? My desk top is just under 100 Feet AMSL and all other factors being equal water has a density that can be considered to be equal to sea level at my office.
6. Is your scale accurate to 1/1000th of a gram? 0.000 g
7. Did you zero before and after?

I have not been able to check your XRF results because the lab I use is on lockdown for Covid (it is a Government Contracted Lab) and I have not found a suitable alternative for XRF testing locally that will allow me to have access.

Based on the XRF test you report the coin can not be genuine. You took the precaution of testing two other 8Rs made before 1850 in Mexico at the same time on the same apparatus, so I have to believe the unit was properly calibrated for gold.

I have never seen a zero test for any silver coming from Zacatecas. When the museum lab (Winterthur Museum Labs) I used when I worked up north before I retired set the standard for gold in Mexican silver over 40 years ago they began with Zacatecas and Guanajuato as silver sources. After years of destructive testing of silver objects from all over Mexico they confirmed that all silver refined in Mexico before 1850 must contain gold. That fact was published in many authentication papers prior to 1990 and I began my use of XRF as a result of their ground breaking work. So to accept a no gold result as genuine, I would have to go head to head with one of the foremost experts in authentication that I am aware of.

Therefore the coin simply MUST be counterfeit.

I know of absolutely no documentation of the Zacatecas mint accepting deposits of silver from private citizens (old silver plates etc) to be re-coined into 8Rs. All of that type activity seems to have happened at Mexico City and the admixture of salvaged silver to their primary mine sources was never significant enough to produce an entire batch run with no gold.

I now have a visual clue - which may be considered by many to be somewhat trivial, but I have one as I noted above.

Now that I have seen the problem I realize that it can be seen on the pictures above.

Anyone care to guess?