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Citric acid and aluminum castings


I read up on previous posts on the method of using citric acid to remove rust from metal parts.

I tried it and it worked wonderfully.

How will it work to clean aluminum parts? Is it safe to dip cast aluminum parts in the citric acid solution?

What is the dark gray film that is left on the metal parts? Should I remove this before painting?

Alvaro Siman
Restoration - Miami, Florida


Hi Alvaro,
I use white distilled vinegar and cream of tartar in a little water to clean Al. Try 1 teaspoon vinegar 1/4 teaspoon cream of tartar, 1/2 pint of water to clean. The citric may work, but it would depend on the citric acid concentration you use for dipping, too strong and you may have problems. The gray film on the Al is it's natural oxide film that is formed when it reacts with air. The film actually protects the metal. I would say to paint immediately after cleaning the oxide film to ensure good adhesion. Good Luck!

Mark Baker
process engineer - Malone, New York


Yes, citric acid should be fine to use on aluminum.

ray kremer
Ray Kremer
Stellar Solutions, Inc.
supporting advertiser
McHenry, Illinois
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The solution is 50 grms to 1 litre of water. I measured the pH and it is 2 to 2.5.

The citric acid is diluted by mixing it with hot water.

Alvaro E. Siman
Restoration - Miami, Florida


Citric acid can be used for cleaning of aluminum (5%)-pH must be corrected to 7-8 (with some ammonia). Pure solution can be used too but it can etch aluminum and remove anodized or chromated/phosphated coatings. Hope it helps and good luck!

Goran Budija
- Cerovski vrh Croatia

December 14, 2008

So could a solution of citric acid be used as a safe alternative solution to deoxidize aluminium before it is then anodised?

Gavin Wilkinson
- Lydney, UK

December 15, 2008

Hi, Gavin. I've never heard of it. The word "deoxidize" is widely used in this context, but incorrectly; the process you are speaking of is really desmutting. I don't think citric acid will dissolve either copper or silicon, which is the principal thing the desmut solution must do. The fact that I haven't heard of it doesn't necessarily mean it can't be done, but I am doubtful. Good luck.


Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

First of two simultaneous responses -- December 16, 2008

Citric acid will dissolve copper, though less quickly than other things you could name.

ray kremer
Ray Kremer
Stellar Solutions, Inc.
supporting advertiser
McHenry, Illinois
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Second of two simultaneous responses -- December 16, 2008

1. What Ted said above and

2. Do not get that messy sticky large-molecule organic acid down in the pores of a casting.
3. Use Nitric Acid 100% plus ammonium bifluoride 2 #/gal.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina

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