Oil of Sharpness

From Dungeon Master's Guide, page 184. Found on Magic Item Table D.

Description
''Potion, very rare. 0.5 lbs.''

This clear, gelatinous oil sparkles with tiny, ultrathin silver shards. The oil can coat one slashing or piercing weapon or up to 5 pieces of slashing or piercing ammunition. Applying the oil takes 1 minute. For 1 hour, the coated item is magical and has a +3 bonus to attack and damage rolls.