| Search our quarter-million Q&As |
Home of the finishing HOTLINE since 1989
-----:Stripping Alodine/Iridite/chem-film from aluminum
Quickstart:
Aluminum is often 'chromate conversion coated' either as a corrosion resistant final finish, or as a pretreatment for painting or powder coating. The process also goes by the proprietary names 'Alodine' and 'Iridite' and the slang name 'chemfilm'. MIL-DTL-5541
[⇦ this spec on DLA] is the most common specification.
This thread addresses how to remove the coating if necessary.
`
• Very fresh coatings can be softened with 50% nitric acid, then wiped from aluminum [credit Max Stein & Brian Terry].
• Older (cured) chromate can be removed with a caustic etch 100-150 g/l NaOH at 40 °C - 60 °C, followed by desmut in 50% nitric acid [credit Max Stein & Bill Grayson].
• Safer for onesy-twosy, but slow, might be baking soda [in bulk on
eBay
or
Amazon [affil link]
and/or washing soda
⇦ on
eBay
or
Amazon [affil link]
in hot water, or possibly a spent zincating solution, or rubbing a thin paste of baking soda with fine scotchbrite [credit James Watts & Dave Wichern].
• MIL-STD-871 [link is to spec at dla.mil / Defense Logistics Agency] offers detailed instruction [credit Stefan van den Berg]
• Remember that the waste will contain hexavalent chrome [credit Jim Gorsich]
Q. What is the best way to strip chemfilm? I am working on writing and SOP on the proper way to strip chemfilm. I need to be able to back it up as well.
Currently they use the desmut tank (nitric, sulfuric, metex etch salts) and then the etch tank for a few seconds which is 160 °F made with Aluminux 1000 at 4-6oz/gal sodium hydroxide.
Chemist - El Segundo
January 27, 2026
This is a meeting place for camaraderie & sharing, not a free consultancy. So some readers don't engage with anonymous posters.
(this entry appended to this thread by editor in lieu of spawning a duplicative thread)
Q. Hello, please help a non-finishing specialist (electronics engineer).
I make use of a hydroformed thin plate, Aluminum 6061-T0, which is to be treated per MIL-DTL-5541, Class 3, Type 1. A few prototypes were done and all was good.
Now we sent all untreated plates to a (different) surface treatment supplier, and all came back with poor electrical conductivity.
Question is how to best recover from this situation. In particular is there any Standard that I can call for, specifying Alodine removal, to ensure the end result is indistinguishable vs. having applied "correct" coating from the start. (If possible without need to test every individual part, before acceptance).
Alternative of course is to re-do the raw plates from scratch.
Thanks very much!
- Geneva, Switzerland
May 2, 2026
A. Hi Sam, hi Stefen,
Thanks to Stefan van den Berg, this thread is now aware that MIL-STD-871 [link is to spec at dla.mil / Defense Logistics Agency] offers detailed instruction. As far as I see, after reviewing that spec, all you should have to do is instruct your supplier to strip in accordance with it.
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
⇩ Similar, related, Q&As -- oldest first ⇩
Aluminum How-To
"Chromating - Anodizing - Hardcoating"
by Robert Probert
You'll love this book. Finishing.com has sold a thousand copies without a return request 🙂
Q. I'm looking for a process that will remove an Iridite (or chem film) coating from an aluminum piece (2024 and 6061) without etching the aluminum.
I would especially be interested in any easy process ... using commonly found university lab equipment. Any information would be helpful.
Thanks,
Kathy PerkinsHarvard Univ. - Cambridge, Massachusetts
1997
A. Kathy,
My response may be disappointing, but I believe there is no such "easy" method: only very fresh (a few hours after deposition) may be softened in nitric acid (typically 50%). You'll have to wipe it off after such operation. Any old, and therefore sufficiently cured coating is only removable by caustic etch: approx. 100 -150 g/L of NaOH at 40 - 60 °C with subsequent desmut in 50% nitric acid.
I would like to add that properly performed, this operation is harmless even to precision machined parts: in 5-15 seconds (time usually sufficient to remove all chem. film) not more than .0001" of base material will be removed.
Max Steincaptive metal finisher - Montreal, Quebec
A. If it is only one or a few pieces, try common bicarb of soda [in bulk on eBay or Amazon [affil link] in hot water. One lb/gal gives a pH of about 9. Will work slowly. You might try a very thin paste with a fine scotchbrite. This will avoid having to do the acid dip and have a lot less waste to get rid of. If you are going to do a lot of it, your lab exclusion might not satisfy EPA.
James Watts- Navarre, Florida
Multiple threads merged: please forgive chronology errors and repetition 🙂
Chemical Conversion Coating REMOVAL from Aluminum
by Biestek & Weber
( Rarely avail. for purchase, but see library holdings on Worldcat.org)
on Amazon
or eBay
or AbeBooks
(affil link)
Q. Hi, I work in the defense industry. We manufactured a piece of aluminum that was originally going to be painted. We thus proceeded with chemical conversion coating of the piece. Once this has been done, we decided to go for hard anodizing of the part (for abrasion and wear properties).
Is there a standard procedure (military or not) for the removal of chemical conversion coating per MIL-C-5541, class 1a, as I understand we cannot anodize a part that already has a chemical conversion coating?
Thank you.
- Montreal, Quebec, Canada
2006
A. Chromate conversion coatings are easily stripped with a caustic etchant with minimal material loss.
Any reputable plater should be able to help you.
metal finishing - San Jose, California, USA
A. MIL-STD-871 [link is to spec at dla.mil / Defense Logistics Agency] provides instructions for "Electro-Chemical Stripping of Inorganic Finishes". In this document you will find process parameters and chemical solutions. Also specific instructions for removing MIL-C-5541 coating.
Stefan van den Berg- Helmond, North Brabant, The Netherlands
September 15, 2014
How to strip chromate from aluminum casting
We have large volume aluminum casting job we do yellow chromate on.
Occasionally we have some which are no good & will need to be redone.
Because they are castings we do not want to etch them to strip them.
We could send them out for a vibratory finish to remove the rejected chromate, but would prefer to do the stripping in house chemically.
Any ideas?
- Long Island City, New York
2007
A. You might try using a spent zincating solution.
James Watts- Navarre, Florida
A. You might try a mixture of sodium carbonate
⇦ on
eBay or
Amazon]
and sodium bicarbonate solutions, mixed such that the final pH is something like 9 - 9.5. It has to be high enough to dissolve the chromate film, but not high enough to dissolve any Al.
Castings can present a real problem in reworks. Once that surface "skin" is broken/etched away, exposed pits and consequent bleed out can make your life a misery.
Dave Wichern
Consultant - The Bronx, New York
Chemical stripping of Alodine 1200 from 7075 OR 2024 Aluminum?
Q. CAN ALODINE 1200 BE CHEMICALLY STRIPPED FROM 7075 OR 2024 ALUMINUM?
MARTIN VOGELENGINEER - HORSEHEADS, New York
May 26, 2009
A. Fresh Alodine 1200 coatings can be stripped by immersion in 50% nitric acid for up to 5 minutes. This will not attack the base material.
Older coatings are harder to remove. I have successfully used a couple of the proprietary deoxidiser solutions, but it is very dependent on age of the coating. You can also use a quick dip in caustic. Be very careful with caustic dipping of aluminum as the solution will attack the base material aggressively.
Aerospace - Yeovil, Somerset, UK
A. Yes, chemical conversion coatings can be removed - most commercial etches will do it fine. If it is an old coating, boiling the parts for 15-30 minutes will make it come off a little easier. The coating itself most likely contains hex-chrome, so make sure that you are either sending it to someone that knows how to handle this, or make sure you are capturing all waste products and treating them appropriately.
Also, you may get much more specific guidance by contacting Henkel - the manufacturer of the Alodine chemicals.
Good luck!
Compton, California, USA
How to Strip Alchromate from Aluminium
Treatment &
Finishing of
Aluminium and
Its Alloys"
by Wernick, Pinner
& Sheasby
on Amazon or eBay
or AbeBooks
(affil link)
Q. I have a processor for the aerospace industry that is struggling to strip Alchromate.
Can this be stripped and how?
Buyer - Kent, UK
August 21, 2017
A. Hi Anthony. Alchromate seems to be a PMD trade name for chem-film/chromate conversion coating on aluminum. You might inquire of them if there is any reason the suggestions on this page might be inapplicable, but I think they're correct. Good luck.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
Sorry! Finishing.com is temporarily Read-Only.
Ted Mooney is retiring but I have several offers to take it over.
We're working hard to make sure we find it the best new home.