Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here


Clear Anodizing Producing Poor Finish

Clear Anodizing Producing Poor Finish

Clear Anodizing Producing Poor Finish


I recently recieved some samples of 6061-T6 Aluminum from a anodizer that were given this military specification: MIL-A-8625F Type II Class I. They showed up like this:


If you can't see, the finish is very bad. Basically it has these water spots that my customer will NOT accept. What I was wondering is:

1. Is finish typical for the spec I called out above?

2. If so, is there an additional etching spec I should be calling out to prevent this?

Thanks in advance  

RE: Clear Anodizing Producing Poor Finish

Class I of the spec you refer to i9n section 3.5 states: "Any natural
coloration resulting from anodic treatment with the various alloy compositions
shall not be considered coloration. The characteristic color Imparted by the
sealing process shall also be considered as non-dyed."

I would argue that the part meets the spec. For true color control class 2 should have specified.

RE: Clear Anodizing Producing Poor Finish

We anodize Type II, class 1.  After examining the pictures, I would say that it looks pretty bad.  I don't think it is a material problem. 6061-T6 is very common to anodizer, and anodizes well. It could be a surface contaminent that is interfering with the finish.  Maybe their pretreament or cleaning processes did not remove the contamient. Sometimes the pretreatment system itself can also cause similiar issues if not properly managed.

After machining, we normally do some type of surface conditioning to remove machine marks or to give a bighter finish.  You might want to consider the same to improve the overall appearance. But I think we would both agree that it must be reworked. If the anodizer it not successful in fixing this problem, I would take my business somewhere else.   

RE: Clear Anodizing Producing Poor Finish

Thanks for the suggestions guys. I had the anodizer redo it and it came back much better than before. No water spots, just some marks due some physical marks on the existing extrusion when we sent it to them.


You spoke about some surface conditioning. Can you elaborate? I was going to sand off the scratches before I send them out but if you know something better....

RE: Clear Anodizing Producing Poor Finish

Sanding is not bad, but you should know that sometimes the anodizer's pretreatment system will bring out or highlight the stratches. Its important to work your way into the finer grits of sandpaper. Don't jump from rough grit straight into a super fine grit.  

We use vibratory tumbling with plastic media, which does an excellent job of removing machine marks (lathe or milling).  

For a rough/satin finish, beadblasting is excellent.

For a mirror finish, buffing with a cotton wheel and polishing compound is excellent.  Anodizing will actually give a slightly frosted finish (with a short hot etch cycle time).

There are a lot options out there to look at.       

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close