There is a problem of staining on AMS 4031 aluminum (0.050" thick) weldment after anodizing. The weld process is resistance welding. A possible cause of staining is copper contamination reacting with the anodize process.

Question:
1. Is there a chemical available that can be applied to the surface of the aluminum that will show if there is copper trace or deposits present?

2. Is there another possible cause of staining?