... During detonation the spark plugs will show very small black or white
spots on the tip of the plug. You will need about a 10x magnifier to see them.
They will be very small balls of melted aluminum (silver specks) or bits of
carbon or cast iron (black or dark purple specks) that gets blasted off the
piston tops, or cylinder heads during detonation. The term "salt and Pepper"
is used to describe this sign of detonation. ....