black·en 
(blăkən)
(blăkən)v. black·ened, black·en·ing, black·ens
v.tr.
1. To make black.
2. To sully or defame: a scandal that blackened the mayor's name.
3. To coat (fish or meat, for example) with pepper and other spices and then quickly sear in a very hot skillet, thereby producing meat that is black on the outside but tender on the inside.
v.intr.
To become dark or black: The day blackened into night.
blacken·er n.