Quote:
Would the silver 68's have a S mint mark (San Fran)?
No, all the 1968 quarters, silver and nickel, were struck in Canada.
All 1968 silver dimes were minted at Ottawa, about half of the nickel dimes were struck in Philadelphia.
There are no mintmarks on any Canadian coins from 1908-1998.
"Dipping" is not considered cleaning...
-from PCGS website