Color variations/spotting problems

I hard anodize aluminium utensils. We have a few problems:

1) There are minor color variations from pool to pool. These are probably due to inconsistent alloy but even material in the same lot have some color variations.

2) There is spotting on some of the pieces. This is more pronounced in pieces that are buffed and not as much on those that are in matte finish

3) What are the job preparation procedures before hard-anodizing. Essentially to clean the job from any grease dirt etc. We try washing in very mild acid solutions but again we get the spotting problem.

Please advise.

Thanking you,

Regarding your #2 and #3 query, it seems that you are trying to degrease your parts with acid solution.

This method may not be working for your application, which may be causing the spots. I think you should use an appropriate alkaline cleaner instead.