"Lloyd E. Sponenburgh" lloydspinsidemindspring.com fired this volley in
. 3.70:

Exposure to H2S (hydrogen sulfide) will rapidly tarnish silver.

Other active sulfur compounds can also work.

Many craft shops will carry "liver of sulfur", which is the potassium
polysulfide mentioned in another response here.

It works _really_ fast on clean metal, so you might end up having lovey
wearing OFF the tarnish, instead of increasing it slowly.

LLoyd