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-----:White Powder/Salts on Anodized Aluminum
Quickstart:
In the anodizing of aluminum the components are immersed into a tank of acidic solution and connected to the anodic (+) positive pole of a power supply. The current separates some of the water in the solution into positively charged hydrogen and negatively charged oxygen. The oxygen is attracted to the positively charged components and converts the skin of the aluminum to aluminum oxides.
Readers new to anodizing of aluminum may wish to view our "Intro to Aluminum Anodizing".
White spots are a perennial problem, especially with black anodizing where they stand out so prominently. See Robert Probert's "Where Do "White Spots" on Anodized Aluminum Come from?" in our on-line library, or --
Read on, join in ...
Q. Hi,
I am experiencing a similar issue with white "powder" or "salts" on cast aluminum aerospace parts. The parts are chromate Type II, Class 3, then Anodize Type II, class 2.
These are coming from a vendor, and I have not yet reached out to them about their process. I attach a photo:
Let me know if this is similar to what others have seen regarding this issue. ⇦ Answer?
Patrick Hawn
Manufacturing Engineer - Portland
June 28, 2022
A. If the spots are "white" then it is probably white aluminum sulfate popping out of the porosity of the casting and could be partially relieved by using a fresh 5% nitric acid post dip after anodizing and before dyeing. If the spots are "gray" then it is silicon on the surface which could be partially relieved by using a fluoride containing deox (but most job shops will only use a wrought metal de-ox).
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
May 9, 2026
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Q. After dyeing of anodized aluminum followed by nickel acetate sealing, snowflake-like white powder accumulates at the sharp edges and corners of aluminum parts. Testing shows the main components are nickel and oxygen. Is this similar to what you have encountered? What are the common causes of this issue, and how can it be solved in mass production? ⇦ Answer?
Xiaofang，Liujob - ShenZhen, China
May 7, 2026
Ed. note: Are your components also castings like Patrick's, Liu, or something else?
Q. 6063 extruded aluminum - Snow-like white ash deposition and corrosion only appear on the workpiece after hanging on the rack for sealing; no abnormal issues occur without rack hanging.
Can this problem generally be improved by adjusting the pH value or formula of the sealing bath solution?
Xiaofang, Liu [returning]- shenzhen
⇩ Similar, related, Q&As -- oldest first ⇩
Q. We manufacture aluminum (62SN-T8 and T9 which is comparable to 6020) transmission valves. The valves are anodized (AMS 2469-D) and then finish ground. The problem we have is white powder that collects on the parts. Infrequently the powder is seen on the parts post-anodize, pre-finish grind. Most of the time the powder becomes evident once the parts dry after finish grind. There is great variation in the problem, some lots will be 100% bad, while others might only be 5%. We make approximately 40 different parts that all have this problem. We are not able to clean the parts to remove the powder, we can only do it manually (think toothbrushes!)
In the past when we ran only 6262-T8 we did not have this problem. It was only after we switched to the lead-free material that we started experiencing this. The rest of the process and our suppliers (anodizing and grinding are outsourced) is exactly the same.
If anyone has any insight on this problem I would be extremely grateful as we are at our wits end trying to figure it out.
Operations - Detroit, Michigan
2007
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 🙂
A. Aluminum How-To lists about 30 different causes for "white spots" and smut. By far the most frequent is calcium salts left behind from the seal, which you see only after the water evaporates. The second most frequent cause is galvanic corrosion usually between titanium racks and stainless tanks/heaters. Come back to us with more information on the racking, tank materials and whether or not the dye and seal are made up with deionized water and whether tap water is dragged into the dye and seal. This problem CAN be beat.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
Is white dust from anodized aluminum harmful
Q. Hi we manufacture signs and name plates. One of our customers machine-engraves anodised aluminium plates which we provide.
We out-source the anodising, though print and seal ourselves.
The customer complains that there is a white dust and is concerned if it is a health issue.
We have asked anodisers for a data sheet, which is not forth coming. So my question: is the white dust harmful?
I have searched web and cannot see.
MONTGOMERY ENGRAVERS LTD - HUDDERSFIELD
September 6, 2018
A. Hello Lee. If you're saying that the parts are free of dust until your customer starts engraving them, and the engraving process generates dust, it sounds like what one would expect. The anodized surface is not metallic aluminum, but a brittle ceramic of aluminum oxide and hydroxides. Depending on the engraving or machining methods, it may come off as a powder or grit rather than adhering.
You may want to insure that your anodizers are not using chrome sealers which could contain hexavalent chrome (but they probably aren't for signs & nameplates).
It's not safe to inhale significant quantities of any dusts regardless of their chemical makeup -- lungs are very delicate micro-machines -- but aluminum oxides comprise more than 10% of the earth's crust, so the dust is probably not a hazardous material I would guess, although it could be of a hazardous particle size (additional opinions and citations are certainly encouraged).
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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A. Hi Ted, - a sunlit though wind rock in the Irish Sea A. In UK, legal limits are defined in "workplace exposure limits EH40", which is available on line.  Geoff Smith Hampshire, England |
A. I guess Lee's wording was somewhat confusing because 3 readers read it 3 different ways 🙂
My understanding was that Lee shipped the plates to a customer, and when the customer engraved them it generated a dust which the customer was concerned about.
I've had emphysema for decades, which I attribute 90% to smoking. But I knowI never had the sense to be careful to avoid inhaling dusts from woodworking, rust removal sanding, dusty attic visits, power lawn mowing, blowing the dust off this & that, smoke from candles being blown out, etc. Now that my lungs are bad, I can immediately feel and know how toxic it is to keep blowing out and re-lighting candles on birthday cakes for the perfect photo ... but I don't recall once in my life any regulatory agency warning us to be mindful about this crap we are coating our lungs with 🙂
Concentrating on 'hazardous material dusts' can have the downside of everyone pointing the finger at "bad guys" while removing focus from what seems to me is the most important issue -- trying to avoid inhaling any smokes or dusts 🙂
In my local TV area, I hear ads from NYC attorneys every night talking about widespread cancer in residents living in the 9-11 area. I don't think it's as important to ascertain exactly what dust material & size is causing cancer as it is to recognize that excessive inhalation of most such dust is a problem.
Perhaps it's possible to do this machine engraving with at least a continuous water wash to capture the dusts?
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.
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