There are a couple of ways to solve this problem. However, in order to do any of them you would have to check with the end user to be sure it is acceptable.
1) Nitric Acid Clean at in a solution 30-50% acid to water.
2) Glass Bead blast clean .002-.006N intensity
Or you might want to look into this link http://www.finishing.com/476/07.shtml
there is a reference to a citric based cleaner that I have tested. It worked fairly well but not as good as the Nitric acid. We have not been able to use the citric based cleaner as it is not yet approved by our aerospace customers.
Walter A. Beach
PO Box 280306
8 Eastern Park Road
East Hartford, CT 06128
860-289-4328 ex. 3
860-289-2134 fax www.peentech.com