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topic 46208

Remove seal on anodized aluminum without damaging dye

A discussion started in 2007 but continuing through 2017


Q. We are developing a process for reworking stained anodized aluminum hardware. We need to remove the nickel acetate seal without damaging the color and sometimes silkscreening. Once clean we will reseal.

Bob Heimann
Product Designer - Centralia, Missouri


A. Hi, Bob. Do you realize that a nickel acetate seal is not a topcoat like lacquer, but involves swelling the pores in the anodized aluminum so that dye and dirt can no longer enter or leave? In this context what does removing the seal really mean to you? If it means reopening the pores, I think it's hopeless, but would like to hear more myself.

Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

simultaneous (2007)

You really need to define stained.
1. If it is a surface phenomenon, you can simply clean it with an appropriate cleaner that will not damage the surface finish.
2. If the stain is below the surface, it is extremely probable that it has actually impregnated the anodize finish. If so, to look good, it will need to be stripped and re-anodized.

James Watts
- Navarre, Florida


I think Ted said the same thing, but here is the way I say it. Once you have hydrated the aluminum oxide molecule which is imbedded with dye , then you cannot de-hydrate the molecule without damaging the dye. You are doomed to completely stripping and starting over.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina
Editor's note: Mr. Probert is the author of Aluminum How-To / Aluminio El Como

September 1, 2017

Q. Hi,

I'm trying to install strain gauges to some anodized aluminum parts (MIL-A-8625, Types II and III, Class 1). I've been told that the anodization doesn't need to be removed, but the sodium dichromate sealant does.

Is there a way to easily remove the sealant WITHOUT removing the anodized coating or damaging the parts? The strain gauge vendor recommends "household cleaner," but that's ambiguous.

Thank you!

Jason December
- Sunnyvale, California, USA

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