chromate conversion
Chromate Conversion: Clear and Yellow Chromate also known as alodine, irridite.

A chemical process that coats aluminum with a corrosion resistant film that can range in color from aluminum white to iridescent gold, depending on customer need. The darker the chromate; the more corrosion resistance it provides (information on salt spray testing times is available upon request.)  Advantages include superior paint adhesion and excellent corrosion resistance with electrical conductivity retained on all surfaces.