I've been doing my homework on separating silver coins from clad and found only four methods that can scientifically work (based on sorting halves):
1) Electrical resistance - this is impractical for many reasons, including requiring > 20 amps to test effectively.
2) Weight differential - look it up, but the difference for 90% (12.50g) 40% (11.5g) and clad (11.34g) - the hitch is a scale with +/- 5% accuracy and automating weighing
3) Coefficient of Restitution (again, look it up) - silver bounces differently off a very hard surface. I have been told the Fed banks use this method to strip silver from the coinage stream. Simple: bounce coins toward a barrier - some bounce higher and over, some don't.
4) Using Lenz's Law: a
counter-
electro
motive
force will be induced in copper when the coins move through a magnetic field. The cause of this CEMF is due to 'eddy currents'. That is, CEMF is a force caused by eddy currents as explained by Lenz's Law. The practical upshot of all this is that if you shoot a conductive object through a magnetic field it will slow down.
#4 Is amazingly easy to try, and works brilliantly on separating copper and zinc pennies. I'm testing it tonight on clad vs. 90% halves and am sure with proper tweaking it will work > 98%. It should also work on dimes and nickels, other tests I'll be trying. The below video is amazing and I have been able to reproduce it spending less than $15 on equipment.
penny sorting - Noah.org
Further, below is a report of my stuffing a bunch of coins into a coin counter at the local Publix - not Coinstar, but a type that has a turntable-like dish in the top where some rejects remain. Will post again when I check more about the machine. Results speak for themselves.
Fiiiinally, I'm heading for my Credit Union on Monday for test #2, a repeat of the below method. An employee swears this Swedish "Scan Coin" device rejects silver, but I seriously doubt she has any idea what she's talking about.
Coin Test #1
Coins inserted:
1964 Kennedy Half
1962 Washington Quarter
1964 Roosevelt Dime
15 pennies
3 nickels (2 US, one Canadian)
4 clad dimes
20 clad quarters
10 clad halves
1 Sacagawea Dollar
1 Large brass Chuck E. Cheese’s token
6 smaller silvered Chuck E. Cheese’s tokens
Total of counted coins inserted = $11.60 in non-silver coins; $0.85 in 90% silver coins (Canadian Nickel not included) = $12.45
Rejects:
4 small tokens
Large token
One nickel (turned out to be Canadian)
1979 Kennedy Half (edges were a tad scuffed up)
Total of rejected coins (US Coins of value) = $0.50
Total Payout on receipt = $12.00
Conclusions: These machines DO eat silver US coins. One token was likely counted as a nickel, and who knows what happened to the other unreturned token.