1810 8 Reales - Fact Or Fiction?

A nice original I would say.

I see no problems here, exept of the average preservation.

:)

Lucky Cuss - Thank you for that link. It looks simple with easy to follow instructions. I'll start working on it tomorrow.

I imagine Swamperbob is travelling to the FUN Show so will hope to hear from him sometime in the next few days.

As said, a typical original (authentic) coin!

I have very few doubts that the coin is actually a Class 2 Contemporary Silver Counterfeit made for the China trade after 1830 based on numerous issues raised earlier on the other thread and as seen on the edge pictures in this case.

I would suggest that added proof lies in the alloy of the coin which could be determined by a laboratory XRF test accurate to a minimum of 10 ppm (0.00001) or 0.001%.

If the coin has a gold content under roughly 0.008 (8000 ppm or 0.8% it is definitely a late class 2 made after 1877 - if it has a gold content over or at 0.008 it is likely an earlier class 2 coin or one made with silver refined before 1870.

Some will say that it could also be genuine. I would add that it would also be exceptionally rare since museum authenticators use the presence of gold to determine historic age of items like silver chargers and statues. For them it is a definitive test - not an unproven theory.

If these non gold bearing silver coins from before 1810 exist it would of course call into question all museum authentications done in the past 25 years.

I may be viewed by some as a bit chipy on this last point. I see it as being scientific. The axiom accepted by forensic scientists in numerous disciplines is that gold MUST be present. Ignoring that fact may be seen as a viable opinion by some but there is no shred of proof.

I am concerned by the results of your SG tests which of course I wish had come out closer to identical.

So I will start by examining the method and figures. You state the weight of the coin in air as 26.86 grams. This result was repeatable. The volume of the coin varied between 2.62 and 2.59 and you postulated that the depth of water above the coin varied.

The problem is that in terms of scientific accuracy - your results were identical because you can only achieve SG results that are accurate to 3 significant figures and the volume change is not adequate to make a difference both result in 10.3 for the SG.

You can not indicate 10.29 or 10.31 - that would be an implied precision that is a "false precision".

This is effectively a perfect SG but actually covers a range of possible alloys from 870 to 920 if the alloy is binary Ag and Cu. Throw in a typical 0.8-1.0% gold (Au) trace and the amount of silver versus copper will drop slightly. But this is getting far more precise than most non-laboratory scales allow.

What type of scale was used to do the test? There is an inherent "error rate" that must be taken into account on a digital electronic scale. I wonder about the scale used because when a coin is fully immersed the depth of water above the coin will not effect the test results.

This in turn leads to the question - did you adjust your results for the volume displaced by the hanger assembly or not. A hanger with a thick vertical element (several strands of wire or a thick string) can actually displace enough water to effect the final results if you change the water level.

Most hangars will effect the SG very slightly for a hair thin wire but thick wires with multiple turns will absolutely effect the SG and the effect RAISES the SG. I use the thinnest 925 fine silver wire I could locate and I subtract the effect it has on the volume (0.01 cc) which I determined based on 6 tests. I marked the beaker so that I use the same water level each time.

Sorry this took a while but we are busy with our office and home move.

The scale you use has a weight range of a maximum of 300g and an unspecified minimum presumptively 0.00g. All small digital scales have an inherent error factor based on the total amount that is being weighed. This factor will vary significantly over the range of weight (capacity) but is closest to correct (producing repeatable results) at the mid-point of the scale capacity. Weighing at or near one or the other limit of the scale increases the error rate to near the upper limit specified. (The range is typically 0.02% to 2% for digital electronic scales I have seen.)

The potential error rates of 1-3% which you recall are a bit higher than typical laboratory digital scales but are seen in the case of inexpensive scales used for weighing gold and silver. For your scale, I would anticipate an error potential of about 2.5% of total weight. The typical error rate curve is a bell shape. The target weight for an 8 R is 27 g that in turn produces a +/- 0.6666 g potential error.

That is very significant error rate when determining density.

The key part of the density formula is the volume of the coin. For a typical genuine 8R the volume of the coin is about 2.6 cubic centimeters (cc).

One cc of volume is represented by one gram of weight so a potential deviation of even 1/2 gram makes the volume portion of the density calculation so inaccurate that density results can not be estimated accurately below one decimal place. That level of results is fine for class 1 coins which are under 700 fine and for most non-silver class 3 counterfeits. But no for class 2 coins.

When calculating density the weight differential in and out of water is only going to be about 2.6 grams so accuracy of that difference is extremely critical. That is why a scale accurate to 0.01 (not one that reads to 0.01 but is not actually accurate) is required. At these error rates it would be preferable to use a micrometer and calipers to calculate average thickness and circumference and calculate the volume.

That is the long and short of a electronic balance scales that cost under a few hundred dollars. An analytical beam balance scale (fully mechanical) can be adjusted to produce a lower error rate and they are typically accurate to the lowest increment on the lightest beam. A 4 or 5 beam balance in an enclosed box (to stop air movement) with a leveling mechanism is really needed to get specific gravity readings for a dollar coin to 2 decimal places. This is the level required for determinations within Class 2.

Your scale would be adequate to isolate Class 1 and some Class 3 coins from genuine but not Class 2.

Regarding the suspension harness - weight is not the issue VOLUME is. Water can be displaced by air that is also nearly weightless. A cotton thread can also have a very significant volume with essentially no significant weight. That is why I use a 900 to 925 fine silver wire which can be weighed and the effect taken into account in the final calculation if needed.

Regarding your other inquiries.

I have never seen a Class 2 Ferdin VII coin with the exception of the transitional portrait style which is fairly similar to the Carolus portrait. I have found suspicious coins of that type but none have passed XRF testing. The Carolus preference had developed by 1814 at least. I believe the counterfeits of Ferdin coins were made for local use in the countries of origin. As for the coinage of other colonial mints these were not acceptable in China at the premium so suspected Class 2 coins of other mints are quite rare and could be early versions made to go along with large Mexican shipments.

RockyRoad You ask



The question almost has no answer because there are so many possible answers. The obvious reply is that there is something wrong because a silver coin will usually ring. A cast silver coin will ring sometimes oddly as would a fractured planchet because of internal voids. An alloy of lead and tin (developed to fill hollowed out coins) can be made that matches silver in density but it is rather soft and lacks the silver color. Therefore you may have a very rare hollowed out portrait 8 reales (none known to exist at present). You could also have an off metal cast or strike in the lead tin alloy - with an electroplate.

So I guess a new thread with pictures would be best.