How to tell if a fake coin is merely coated with silver?

Hi,

There are countless fakes and replicas of famous silver coins. Many are very well-made fakes and they're merely coated with silver.

I'd normally:
- weigh the coin, compare the weight with the officially-published weight (but sometimes the weights are close too, so it's difficult)
- would probably look for design defects (but nowadays even the expensive Krugerrand Gold coins have defects)
- sound test?

 

• Neodymium magnet (as silver is very slightly magnetic, so earth magnets can be used)
• Sound test
• PM verifier (brand: sigma etc)
• XRF

I would personally discount the first two and have a PM verifier as a base for peace of mind, and a well worthwhile investment IMO.
XRF too expensive for the everyday stacker, unless your one of the big boys.

 

Magnet test..

 

Yep, neodymium magnet test is the easiest and best way to check that.

 

I would think that there reason that the magnet slides slowly across the silver is not because it is slightly magnetic, rather that it is such a good electrical conductor that the moving magnet generates eddy currents in the silver that set up an opposing field that slows the magnet’s movement.

 

Yep, Silver is diamagnetic meaning that when place in a magnetic field it generates its own magnetic field that repels the original field.

 

rare earth magnet is an ok test for a quick test, but silver is not the only metal where a rare earth magnet reacts like that so it can be fooled.
XRF is obviously the best but not many people can afford the machine, or have access to one.
The water gravity test is a pretty good method as you cant fool that easily even if the bars are hollowed out and filled with something else.

 

I do have neodymium magnets and I do perform that test as well. It usually works...

But sometimes it is rather difficult to monitor/observe the magnet slowly slide down:
- it might slide down slowly even if the coin is some non-silvery allow, but due to the engravings/grooves on the coin is is slowed down (therefore the slide)
- one might have to repeat it endlessly and it might seem confusing
- some coins are too beautiful (like Lunar Dragon series) and one just wouldn't even touch it (let alone put another metal on top and let it slide!) - if you do this to an encapsulated "gem" coin... it's like committing suicide

 

gravity test video

 

XRF is only surface, it may not help with a plated/coated fake depending how thick it is. I don't know how thick XRF goes, but we are talking micrometers.

 

Ultrasound devices will tell the speed of sound through the sample. It sends sound pulses and listens for their echo. By knowing how thick the metal is you can work out the speed of sound in the metal. Every metal has different sound properties.

 

I use the smallest neo magnet for the slide test. They are about 7mm wide. And because they are so small I always keep one in my wallet in case I happen to unexpectently come across a good buy.

 

I've think I heard it's about 60microns (about the thickness of a human hair), but it depends on how long you test it for. The longer it's tested the deeper it goes, but the max depth is probably 60 microns.