Pickman's Blade

Pickman's Blade is a unique combat knife found in Fallout 4. It is obtained from a Master locked safe in Pickman Gallery, the key to which is a reward from the quest Pickman's Gift.

Characteristics
The blade actually has two distinct abilities. The first is its Wounding effect, which causes targets to bleed for an additional 25 points of damage. The second is a pre-equipped stealth blade mod which deals an additional sneak attack damage multiplier of 0.6, as well as causing targets to bleed for an additional 25 points of damage. This stacks with the weapon's legendary modifier for 50 points of damage from bleeding per hit, and bleeding effects currently stack per hit, making this an extremely effective melee weapon even against higher level enemies later in the game. The 'Stealth Blade' modification can be removed, and then reapplied to another Legendary variant of the Combat Knife, combining both effects.

If not used by the player, the knife's high damage and speed makes it an excellent weapon for Cait.

Location
The weapon is located inside a Master-locked wall safe, behind Pickman's painting "Picnic for Stanley". In order to get the key, you must work your way through the gallery and the connected sewers, and rescue Pickman from a group of raiders. Afterwards, when talking to him, he will express his gratitude, give you his key and tell you where to find your reward. Alternatively one may let the raiders kill Pickman then loot the key off him later, however, this will not prompt the player to go to the painting.

In order to find the painting he is talking about, return to the front door, then immediately enter the room on the left side of the hall. It will be a picture of a man's face; when the reticle is placed on it, you will receive a prompt to take it off the wall. This will reveal the wall safe, and within lies your prize, along with some caps and a thank you note.

Behind the scenes
The knife is a possible reference to H.P. Lovecraft's short story, "Pickman's Model" as the main character of the story is Richard Pickman, a painter.

It also resembles the Ka-Bar combat knife issued in the US Military.