How was this made? (Aluminum Heat Sink - Mystery Manufacturing Method)

[Leav]

Ripped this heat sink from an pc, and I am stumped as to the manufacutring method used to make it.

First here's the full gallery.


now to individual descriptions:

General View
Shiny Side
Dull Side - Showing aluminum grains
Single fin - shiny side
Single fin - dull side
Side View 1
Side View 2


The mystery to me is all about the individual fins: Why and how do they all have one dull, and one shiny side?

How was this made? is the shiny/dull intentional or a byproduct of the manufacturing process?

The side views are included as they give a clue (I think): they show that at the bottom all fins have slight radius to one side.
Also, the top of each fin has a noticeable edge.

A lot of people have a lot of experience here on chiefdelphi, so I was hoping someone could bring me in on the secret!

Thanks!
-Leav

Edit:
The heat sink has lots of fins broken off because I was.... investigating them...