1808 Carolus Llll 8R, Authentic?

The type of XRF used at coin shops is good enough to indicate the silver and copper content. I don't believe it would be powerful enough to detect the trace amount of gold that should be present in the silver processed in Mexico at the time your coin would have been minted if it was genuine. Silver ores extracted from the main mines in Mexico contained gold and the technique to separate out the gold was not greatly improved until the late 1800's (the MacArthur-Forrest cyanide leaching process was developed in 1887). swamperbob gave the figure of roughly 0.3 to 0.4% gold detected in genuine 8 reales using laboratory quality XRF. If at all possible, have your LCS attempt to detect gold in your coin.

Well,I stopped by the LCS and He wasn't too busy today,so I had Him shoot the coin.Here are the results of His machine.
AG 96.7738
AU 0.0758
CU 2.9006
ZN.1975
Ni 0.0298
Pb 0.0225

I was asked to comment so here goes.

Visually the coin has many of the ear marks listed in my book which I use to isolate probable (likely) silver counterfeits of the type that were made in and around Boston between 1870 and 1930. These are late Class 2 made after the Comstock discovery in Nevada. The dies show repunched elements, soft surface lumps, poor surface finishing, the planchet shows surface cracking from cold or cool drawing and/or lamination, dentil issues (are probable - hard to be sure from these pictures), The edge dies show squared circles in the edge design, variable segment shape and spacing and the presence of diagonal straia on part (half) of the edge. The laps appear to be opposed (roughly) but the length is obscured by the deepest diagonal straia as is typical.

So likely Counterfeit - one of the millions made for use in China to take advantage of the premium.

I would next do a Specific Gravity test to confirm a density of about 10.3. A density of over 10.25 is typical of Class 2 UK and US origin coins. Chinese Contemporary circulating Counterfeits in silver are said to be about 10.20 but I have yet to scientifically confirm one of those. The Chinese density is as stated in a Royal Mint test of Chinese counterfeits found in circulation in Canton in 1835 that were tested in London at 800 fine or lower. It is my current opinion that the UK used primarily 850 fine silver to strike 8Rs before 1835 and variable contents up to 925 thereafter. Whereas the US used 900 fine silver which was the US mint standard.

Coins under 800 fine can be easily detected by SG tests accurate to ONE decimal which can be done using a scale accurate to 1/100th of a gram. Accuracy of the scale is what is critical NOT WHAT the scale reads. Many cheap scales (particularly digital scales using Chinese chips) will read to 2, 3 or even 4 decimals when there is a 0.2% stated accuracy in the fine print. That means any reading taken should be expressed to 1 decimal when weighing an object that weighs 27 grams. So if you get a reading of 10.2 instead of 10.3 (round off all places after 1) you have a counterfeit in the 800 fine range not 900 fine.

After doin SG, weight and ring tests the next step is XRF. You do need to know how to read the results. There are beginner errors that abound. I was guilty of some before I read more extensively on museum testing of silver art works.

The first criteria is the power of the X-ray signal. The more powerful the deeper a reflected signal will be detected by the reader. Hand held guns like those in jewelry shops, coin shops and junk yards are low power and read mostly surface returns. Half to one quarter of the thickness of a human hair is typical for gold.

A laboratory unit is far stronger in terms of X-ray beam strength. This results in a DEEPER reading. You also need to be aware that the more dense the target metal the more likely there will be a strong reflected signal. That returning signal must escape the metal surface to be read by the unit. Typical lab units penetrate 2-4 times deeper than hand held units.

The surface of a coin unlike a museum piece can not be cleaned BEFORE testing. So steps must be taken to modify the results. The surface of an uncleaned coin has surface debris - corrosion products especially Iron in the form of rust is typical. Read Iron with skepticism.

Also screw press struck planchets were typically annealed (softened) by heating them BEFORE they were struck. Each time a coin is heated some copper in the surface is lost. After the strike the completed coins were usually soaked (washed) in heated acid to remove scale and toning. This had an added effect of enriching the silver surface. The combined effect seen on both genuine and contemporary counterfeits is an apparent increase in silver and a corresponding loss of copper content the closer to the surface you are.


Based on the results of the XRF test and presuming it was done on a typical handheld gun - the coin is a Class 2 Silver Contemporary Circulating Counterfeit almost beyond any possible dispute. The tests done in fully detailed (showing all figures not just orders of magnitude) scientific reports gives rough limit of 0.4% to be certain that an artifact or coin was made in Colonial Mexico (pre-1820).

The silver versus copper ratio using a handheld gun will always read too high in silver and too low in copper. That is exactly what I see here 96.8 Ag and 2.9% Cu. Copper is not very dense and produces the weakest return signal of the primary critical components. Silver is denser and returns a signal from up to two times deeper. Silver surface enrichment is also normal so I believe they started as raw 90-10 nominal alloy planchets.

Since the gold content even of a hand held gun will be accurate to 0.1%, the handheld gun is completely acceptable to screen out Class 2 silver counterfeits made AFTER 1880.

Here the gold result is expressed as 0.0758. This is a figure that is expressed to 4 decimals when there is no scientific accuracy to any greater than 1 decimal. However, one decimal is all we need. Therefore I would say with a high level of confidence that the silver used to make this coin was definitely NOT mined or refined in Mexico in 1808 or any date before that time.

This coin as a Class 2 coin is for the present as valuable as any comparable genuine coin. The reason is that testing (correct scientifically valid testing is not done). Having seen over 300 tests so far, I believe that the number of Class 2 coins is almost equal to the actual number of genuine survivors. About 1 in 2 coins tested will confirm as counterfeit.

I hope that helps. Remember even the contemporary counterfeits are valuable, the only fakes that should be destroyed as shown in the clip are Numismatic Forgeries - the ones made solely to defraud collectors.

Thanks!Some really good information there for sure.
The machine He uses is box about 18" square,hooked up to a computer,not one of the hand held ones.If that makes a difference.

Cross-eyed It sounds like an older desk top lab XRF. It is kind of small to be the really high power unit now being sold which can produce accuracy of 20 PPM.

How long did the test run? A one minute sampling on a well calibrated new unit is decent to 200 PPM but 10 minutes is optimal for a lab reading of 20 PPM. The hour readings can read to 2 PPM (with risk of damage and a $500 charge). At almost $10 a minute the charges ramp up quickly.

When I go to the laboratory my experience has been no more than 8 full tests with computer correction results per hour. In these cases the resulting report can take about 1 week to receive after the raw lab work is complete.

The raw results are always altered by the final computer resolution of the results to eliminate false level detections.

In 2 minutes what you received was a raw test. Did the report include a statement of range of accuracy +/- for each element?

That would be good to know. If say the results are accurate to the 3rd decimal place it would not mean the coin was genuine and it would make the very high silver readings very hard to account for.

Cross-eyed The identification of the unit as a Quickshot RXF,79T+ is adequate to establish the accuracy of the device for the purpose at hand.

It is a desktop version of a Handheld unit that was specifically designed as a GOLD tester. The large chamber was made to accommodate larger objects for testing. The unit has a focusing feature to allow spot testing of various points on the object. It costs about $3,500 brand new and far less on the secondary market.

The level of repeatable accuracy has a stated standard deviation of 0.3 to 0.9%. The results are therefore within almost 1 percent plus or minus.

The unit is not a laboratory type testing device and will not produce a correct alloy profile for silver coins. The results are subject to the same corrections that must be applied to a Handheld unit. So my initial appraisal of the data was correct.

This unit was designed for gold buyers and for that purpose it is very a good instrument. The standard deviations are acceptable for buying gold salvage. It is also adequate to establish that a silver item has the requisite gold content to show that it MIGHT be genuine. Likewise it is adequate to identify as a counterfeit a coin that does not contain the requisite amount of gold.

Therefore an authentication unit for older pre-modern coins it is OK as long as you are interested in gold levels. If you were trying to identify an 1830 silver 8R made in Birmingham, England your project would be a complete failure.

Does the coin dealer buy silver scrap using this same apparatus to establish his purchase price? If he does he needs to increase his margin or he will make less profit than he anticipates.

Also a sharp seller could defraud him if he boiled 500 fine silver in an acid that would leach out the surface copper to a depth of more than 50 microns. Tests I have seen can take a 500 fine coin and make it appear to be 900 fine after a period of about 6 hours. Of course the porosity of the surface has to be rolled or hammered flat. This would not work on most coins but would in theory work very well on scrap silver.