The Black Cap

The black cap – based on court headgear in Tudor times – was traditionally put on by judges passing sentence of death.

Ok, if you look this thing up on the internet it's usually called a "flat sheet of cloth" or "a plain square of black cloth", which is completely wrong.

This is demonstrated by the model's head being covered by the thing in the third picture. 

I would desribe it more like a floppy mortar board with the top portion being a square on top of a piece with a hole in it where the head fits in.

 There's a lower part which is a triangle. This is like the thing on a mortar board where one's head fits in.

But the real hole isn't that big, which is why it looks flat on most adult heads, but you can get an idea of how it works on the more lifelike (and larger statue). 

So it's actually a square with a triangle under it.

The lower triangle drops down when the cap is on the head. You can see the points sticking out on the bottom of the lower picture.

You can also see them on the top picture, but not as obviously. 

So, a better way to describe the thing is that it's like a floppy mortar board. 

It is in no way a flat piece of cloth. 

And, yes, this the the real thing.

Since there is a definite hole it it, the reason one corner is pointing out is that's the only way it can be worn. Unless the wearer wants the corner on the bottom to blindfold him.

I'm not a tailor, but I would create a pattern for this which would be three silk squares 33cm (13"). The first wouldn't have a hole and would be the top. The next two would have holes in the centre. One would be sewn onto the top. The other one would be folded in half to make a triangle. It would be sewn onto the hole in the middle piece.