Silvered Weapons

Some monsters, such as werewolves, are susceptible to attacks made by silvered weapons. A single weapon, 30 arrows, 10 crossbow bolts, or 20 sling bullets can be silvered at a cost of 500 gp. This cost represents not only the price of the silver, but the time and expertise needed to add silver to a weapon without making it less effective.

Published in Player's Handbook, page(s) 220, Rules Compendium, page(s) 269.