Where do I find a black robe?

Hint 1 of 12:

The first thing you need is a piece of fabric.

Hint 2 of 12:

You'll have to borrow one from Death's house.

Hint 3 of 12:

Rip off one of the curtains in the hallway -- the one on the left side,
closest to the staircase, to be precise.

Hint 4 of 12:

It's not quite black enough for your purposes yet.

Hint 5 of 12:

You'll need to dye it blacker.

Hint 6 of 12:

Find something else in Death's house that's black enough to dye it.

Hint 7 of 12:

There's a pot of ink in the study.