Bolivia 8 Reales 1790 - Authentic Or Fake?

Hi and thanks for your reply.

Your comments are enlightening, I do not know much about these coins myself - only what you can get out of Krause.

The weight of the coin is 25,7-25,8 grams, so it is underweight - possibly because of the removal of the edge. But it does appear to have the right diameter. The seller does not know more than me, he picked up the coin from a miscellanoeus antiques auction where no information of the objects were given. He resold it on the strength of the two pictures I have posted here, and did not guarantee anything besides delivering the pictured coin. He has even so offered me to return the coin if I feel uncomfortable with it, but I rather like it and would probably want to keep it if it is real. But I am not interested in fakes (irrespective of production date). I know some comtemporary fakes have higher value than the real coins they imitate, but still they do not appeal to me.

I paid approximately 90$ for it.

The wrong portrait and the use of "IV" rather than "IIII" are in fact perfectly normal on the Potosi mint coins of 1789/1790 (see Krause, KM# 64), but the other things mentioned are cause for serious concern - notably, the lack of the squares-and-circles edge pattern.

I have a fake Spanish dollar, too. It looks pretty good (except for a couple of places where the silver has come away, showing a copper core) but the edge is like yours, just a crude attempt at reeding. It fooled me when I bought it (never having seen a real one before), but it didn't fool an expert in Spanish colonial I showed it to.

Litotes The design is correct for 1790. The portrait of Charles the III was used with the legend Carolus IV for about a year in 1789 and 1790 following the death of Charles III. In 1790 the legend was changed to Carolus IIII. These "transitional varieties" have always been interesting and have been sought out by collectors to complete type sets. For that reason they have been forgery targets for a long time.

This particular coin would have been edged with the Circle - rectangle design not the lotus blossom. The lotus edge was used on the Dos Mundos type not on portrait 8Rs.

The weight of your coin is in all liklihood TOO low to be real unless it was struck on an exceptionally large planchet. If you do the math, you need to remove about 5% of the weight (The coin is 95.4% of original). I have a few Bolivian coins with a diameter of 41 mm. So assuming a 41mm start you need to remove 1.92 millimeters from the diameter of the coin. That is a lot of metal considering the appearance of what is left.

You need to perform a specific gravity on the coin to see if the metal is dense enough to be silver. The color and the staining patterns look like an off metal to me.

I believe it is far more likely that the coin is a cast copy and that an edge seam was removed by filing. Copies made in the 1950s were sometimes made without adding an edge design. The edge was omitted so that they could not be charged with forgery. There are some suspicious lumps in the field and the details do look weak.

Let us know if you can get the SG.

Litotes - Specific Gravity is easier than most people think. I can't find the links but the displacement (volume) of the coin is equal to the change in weight of the coin weighed in air and the coin weighed immersed in water.

If a coin weighs 27.00 grams in air and 24.38 grams suspended in water. The volume of the coin is 27-24.38 or 2.62 cc. Water displaces 1 gram per cubic centimeter (pure water at standard temps). The weight in air divided by the volume gives the specific gravity 27/2.62. The only trick is to find a method of hanging the coin and making a small adjustment for the displacement and weight of the hangar.

I left out the math on the calculation of the diameter reduction it is not just a straight percentage. The thing you are missing is that I did a ratio of surface area of the coin. Any 2 square mm of the coin will weigh the same regardless of the position on the coin.

The weight of a coin is roughly proportionate to the area of the coin (assuming uniform thickness). That assumption is valid for this mathematical precision in this calculation.

The weight ratio is 25.8/27.03 = 0.9545 so therefore that is also the area ratio. The coin has been reduced in surface area by nearly 5%. I wanted to calculate the amount of lost surface area and convert that to a band of unknown thickness around the outside perimeter of the coin.

So I expressed the two areas in terms of the original radius and the amount of material lost by filing called Y.

The area of the coin now is Pi x R x R (pi R squared)
The original area is Pi x (R + Y)x (R + Y) where Y is the lost radius.

I called the present area A1 and the original A2. So since the ratio of the areas is equal to the ratio of the weights.

A1/A2 = 0.9545

I substituted the two formulas getting.

Pi R1 squared / Pi (R1 squared + 2R1Y + Y squared) = 0.9545

Then I resolved the equation using an original 41 mm diameter

Y squared + 82Y - 80 = 0


Then I solved for Y using the quadratic formula.

I don't have the fonts for math terms but the formula is a high shool math thing.

The fact that the change in radius came out to a final ratio of 4.78% is just coincidence based on the starting diameter in this case. If you did the calculation for a far larger change in diameter the ratios would be considerably different.

The reason I omitted all the math was the difficulty most people have with math. Plus I was also in a hurry.

An open platform balance works fine to measure specific gravity. Put a beaker of water on it and zero the scale out. Then suspend the coin in the water from a rigid support (I hung the coins from a ring stand using a piece of thread). The scale will show the weight of the water the coin displaces, plus whatever you used to hang it in the water. The thread I used added about .01g.

What I meant by "lotus pattern" was the serrated design on the top of the rim - sorry if I used the wrong term. It still bothers me that there is virtually none of this seen on the obverse.

There are three different "standard" edges used on the 8R coins of Mexico.

The first called the "Lotus edge" is a series of lotus flowers (they often look like leaves) - this edge was used from 1732 until 1772 on the Dos Mundos (Two World's) Pillar 8 reale.

The second is usually referred to as a "Colonial Edge" is used on the Portrait 8 Reales from 1772 to 1823. It consists of alternating circles and rectangles.

The third form is the edge seen on the Mexican Republican issues from 1823 to 1897. It is usually called an "Engrailled edge" and looks like a series of parenthesis or brackets - sometimes with or without a dot. {{{{{{{{{{{{

In all cases, there are varieties by date and mint. The edges alone make a very interesting collection. At times, there is a style change and only one of the edge dies gets changed - it makes an odd looking coin with two different edge patterns. There are also double and triple edged examples (after about 1880 in the Mexican series). Of course the counterfeit edges are the MOST interesting because of the range of variation.

Each of the other Spanish Colonial mints seemed to adopt a different style after they became independent, so edge studies are a field that is wide open for the researcher.

That's great - I like a happy ending.

I just received an 1803 counterfeit 8R that I won on ebay. I bought it thinking it was a modern Chinese copy (because of the way the add was worded), but it is a very old copy made of silver. The edge design is the only problem - it has two laps but the shapes are not exactly correct and HALF of the edge has HORIZONTAL grip marks. It is a variation on the more normal half Diagonal marked edge.

The coin was an ANA reject (Money Museum). They identified it as a forgery. Silver struck and over 26.5 grams.

I will post pictures later.