[bobcowan]

Powdercoating is a coating like a very tough paint. It forms a layer on top of the material. It adds thickness and weight. And it will prevent corrosion. It can be removed.

Anodizing is like a stain. It penetrates the first tiny bit of the material and "stains" it the color you're after. To me, it looks more like a tint than a coloring or coating. It does not add thickness or appreciable weight. It somewhat seals the surface of the material, and will prevent some corrosion. It can't be removed, except by removing a layer of material. Anodized alum can be polished. It will hold it's shine better than billit alum.