via HACKADAY: Old Ham Wisdom Leads to Better Aluminum Painting

When [bdk6] tried painting aluminum for electronic projects, he found it didn’t tend to stay painted. It would easily scratch off or, eventually, even flake off. The problem is the paint doesn’t want to adhere to the aluminum oxide coating around the metal. Research ensued, and he found an article in an old ham radio magazine about a technique that he could adapt to get good results painting aluminum.

Actually, paint apparently adheres poorly, even to non-oxidized aluminum. So the plan is to clean and remove as much aluminum oxide as possible. Then the process will convert the aluminum surface to something the paint sticks to better. Of course, you also need the right kind of paint.

The key ingredients are phosphoric acid and zinc phosphate. Phosphoric acid is found in soft drinks, but is also sold as a concrete and metal prep for painting. The zinc phosphate is part of a special paint known as a self-etching primer.