Q. A customer of ours has asked us to conduct a bleach test on its parts that have been sulfuric acid anodized, dyed and sealed. Supposedly, this bleach test is a way to check if the parts have been sealed properly to prevent premature fading of the color. What I have learned is that there is a sort of "back pocket" approach for using a bleach test, but there is nothing written or documented that supports this "bleach test." Please tell us anything you can. G.M.
A. The reason you can't find an answer to the "bleach test" questions is that there is no bleach test that is recognized as a standard test for evaluating the quality of seal for anodic finishes. I can see no reason why a customer would request this type of "test" unless, of course, he has developed a scientific procedure for evaluating the quality of seal that is exclusive to his operation. Do you know the product application?
The correct test for evaluating the quality of seal of an anodic coating is ASTM B 680-80, "Standard Test Method for Seal Quality of Anodic Coatings on Aluminum by Acid Dissolution." ISO 3210 is the same test. This test method calls for evaluation of seal quality by determining the coating weight loss of a sample coupon when immersed in a solution consisting of 20 g/liter chromic acid, 35 g/liter of 85% orthophosphoric acid and 1,000 ml distilled or deionized water. The solution is heated to 100F, the coupon immersed for 15 min, rinsed, dried and weighed. The weight difference before and after is the weight loss. According to AAMA Publication 611-92 (or later versions) the maximum allowable weight loss for an adequate seal is 40 mg/dm2. If the weight loss is 40 or less, you're okay.
Don't do the test from the information above. Get a copy of the procedure and set it up properly in your lab. If I were an anodizer and was asked to certify to a "bleach test," I would recommend to the customer that the ASTM procedure be used to evaluate the quality of seal. If the customer insists on the other test, I would tell him to find another anodizer, no matter how big the job is.