A Primer on Anodizing Metal

You may have heard of the term “anodizing” but got confused about what it is exactly. Here’s a quick guide that explains all you need to know about this electro-chemical process.

What Is Anodizing?

Anodizing is a process that adds a thin layer of oxide to the surface of metals, though aluminum is most commonly anodized.

How Does Anodizing Work?

To anodize metal, you have to fully dip it into an electrolyte bath – most often chromic acid or sulfuric acid – along with a cathode. Doing this creates an electrically conductive layer on the metal. A charge is sent through the acid, which causes the cathode to release oxygen ions that form on the surface of the anode (the metal, which becomes a positively charged electrode). The end result is a film of metal oxide growing on whatever is being anodized.

Can You Anodize Metal at Home?

Some people have successfully anodized metal at home, but it is better to leave the process to a professional who uses a safe anodizing tank.

How Thick Is the Oxide Layer?

A standard anodizing process creates a layer that is approximately 0.00001–0.001 inches thick. You can hardcoat a metal piece, which can form a layer that is 0.001–0.005 inches thick.

Why Would You Want To Anodize Something?

There are two main reasons to anodize aluminum alloys: to protect them from corrosion and to decorate them. The anodization process naturally leaves a strong, shiny clear film. However, the coating is porous, which allows it to absorb colorful dyes. Because the aluminum oxide is not applied to the metal’s surface – it’s not painting or plating – the oxide layer will not peel, scratch or chip away. It essentially grows a protective layer.

Anodized metal is used in everything from home appliances to skyscrapers. The next time you pick up a metal flashlight or use a carabiner clip, you’ll know exactly how the metal’s colorful, durable surface was formed.