The way I understand it, Anodize is not a finish which is applied to aluminum but rather, a process where the aluminum oxide is enhanced with chemical baths and electrolysis.
This from the Aluminum Adodizers Councilhttp://www.anodizing.org/what_is_anodizing.html
...anodizing is accomplished in five carefully controlled, calibrated, quality-tested stages:
1. Cleaning. Alkaline and/or acid cleaners remove grease, and surface dirt.
Etching. An appealing matte surface finish is created with hot solutions of sodium hydroxide to remove minor surface imperfections. A thin layer of aluminum is removed to create a matte or dull finish.
Brightening. A near mirror finish is created with a concentrated mixture of phosphoric and nitric acids which chemically smooths the aluminum's surface.
3. Anodizing. The anodic film is built and combined with the metal by passing an electrical current through an acid electrolyte bath in which the aluminum is immersed. The coating thickness and surface characteristics are tightly controlled to meet end product specifications.