You ask
Quote:
is there any definite way to tell if this coin is 'legit' or not?
The best way is to examine the coin critically - do not accept anything as being real or fake without proof.
Start with the physical aspects. Is the coin magnetic? I would not think so but check. Silver is NEVER magnetic. A magnetic coin is a fake. No need to go further.
Then move to the weight. Does the weight make sense? A coin to be real must weigh very close to a standard weight. DO NOT AUTOMATICALLY ACCEPT a low weight as caused by corrosion. It can occur but the effects will show. Is the coin corroded UNIFORMLY? Corrosion removes HIGH RELIEF details first. Since this coin shows high relief - there is essentially no way to account for a reduced weight by corrosion - that didn't happen. So look for a weight in line with the genuine original. A coin that is more that 4% low in weight will be a COUNTERFEIT.
Finally rule out clipping of the edge as a reason for loss. If it is not present the coin is fake and there is no need to go further.
Then check specific gravity. This is a simple test. It is done in high school. Take the weight of the coin in air and in water. The difference in grams is the exact volume of the coin in cubic centimeters. The weight of the coin divided by the volume is the specific gravity. A real 90% silver coin has a specific gravity of 10.31. A difference of 0.1 is enough to diagnose a forgery. Copper or bronze coins are close to 9.0. So if you do not get 10.3 you can stop the coin is not silver. If you get 10.3 it does not prove the coin is genuine just silver. SG tests allow you to know if you have silver without being destructive.
Then check the edge with a good microscope for traces of a mold seam. The actual seam, vent and sprue will be someplace on the coin but forgers can be deceptive. The sprue and vent can be place most anywhere but the seam in the mold is usually around the edge. The forgers grind them down. So look for evidence of grinding along the edges (parallel grooves of uniform depth in a layer.) Really good forgers will cross grind the edges to confuse the trace but it is visible. Uniform edge grinding on a coin that was already rare by the time power equipment was invented is a positive proof of forgery.
Then use the microscope (binocular) to examine the surfaces of the coin. You are looking for evidence of casting - air or gas bubbles at the surface or pores from the die that leave raised spots. You are also looking for evidence of striking - 90 degree intersections between field and lettering or metal flow lines from striking. These coins were not cast. So you must have reasonable proof that the coin was in fact struck.
Most cast copies are made from cast molds so you look for evidence of casting in the form of scratches that were on the coin when it was cast. Damage to a coin shows lines parallel to the direction of the impact that caused the scratch. A cast of a cast usually looses most of that detail. A scratch or dent that does not look like a scratch when magnified is proof of forgery.
Once you have done these checks you will KNOW this is a recently made cast copy. There will be no actual wear visible - surfaces will be artificially aged. There should be ample evidence of casting.
I actually suspect that a photoengraving or early computer assisted engraving technique must have been used to make this mold. The lettering and details are far too high to be a hand struck cob. The features are NOT SHARP.
When a coin passes all these tests and questions still remain you can get an XRF or SEM test to determine the actual metallic contents. These are expensive tests but they can prove a coin is a forgery made with metals that are too new to have been in use in the 1600's.
There is ZERO chance the coin is genuine but you do need to prove that to your own satisfaction.
Posted 02/26/2013 01:20 am
