Sorry. Wrong Forum.
I was mortified recently to empty a safety deposit box and find hundreds of Gem Swiss moderns tarnished and spotted. This included 95% of the coins in the mint sets. I tried a few methods with little or no luck until turning to the old tried and true two day soak in 91% isopropyl alcohol. This fixed 75% of them.
If it's like most hazing and tarnish on modern coins the longer it stays on the less the chance the coin can be saved. These coins are apparently all quite scarce already since mintages are in the 5000 to 15000 range and they've never had much of a premium to face value leading to extensive destruction.
Acetone is usually the most effective on moderns but it won't always completely remove tarnish. I've lost some very scarce and Gem moderns over the years to various types of tarnish. People need to dismantle almost all modern US and world mint sets or there might be very few coins left for future generations. Most mint sets were made in tiny quantities and are seldom seen. There are lots of proof sets out there but mint sets often weren't made at all and where they were it was in tiny quantities. Attrition was already severe even before the poor packaging has started ruining so many.