From the Arctic Silver Instructions as posted on the web site: (Emphasis added)
1. Arctic Silver II can be removed from CPU cores and heatsinks with isopropyl alcohol or acetone (nail polish remover) and a bit of brisk rubbing.
If Arctic Silver II compound gets on the CPU ceramic, it can be removed with any dish detergent (Dawn, Lux, Palmolive, Etc.), WD-40, citrus based grease removers (Goo Gone, Etc.), Xylene based products (Goof Off, some carburetor cleaners), or an automotive degreaser.
(Do not use soap for an automatic dishwasher.)
Never use any oil or petroleum based cleaners (WD-40, citrus based grease removers and many automotive degreasers) on the base of a heatsink. The oil, which is engineered to not evaporate, will fill in the microscopic valleys in the metal and significantly reduce the effectiveness of any subsequently applied thermal compound.
2. If you use any of the suggested products to remove Arctic Silver II from the CPU ceramic, always do a final cleaning with isopropyl alcohol to remove the residue from the cleaner.
Nevin House
Arctic Silver LLC