Summary for skin products affecting anodizing Discussion
skin products affecting dyed anodizing is the likely issue here, but the thread points to two different explanations. Kevin Enter describes a Type II anodized shaving razor whose dyed color seems to disappear mainly in high skin-contact areas, even though thickness and dye stain tests look acceptable. M. Stammerjohann suggests the shaving cream may be alkaline enough to attack the seal over time, exposing the dye; he recommends testing parts with prolonged exposure to different shaving creams and checking pH, noting that anything over about 9 can be a problem. ALAATTIN TUNA says the issue may instead be poor sealing quality, since a dye stain test alone does not prove sealing is sound; he recommends a weight-loss test and says anodized layers are generally only resistant in roughly pH 4-8. The discussion therefore leans toward alkaline skin products or sweat interacting with imperfect sealing.
Q. We are a machine shop with our own Type II anodizing line, producing a consumer product (safety shaving razor). We have recently had several instances where customers have had the dyed colour “disappear” from their product. In some cases the way the dye has disappeared looks like it is primarily in the areas where there is the most skin contact (hand and face). The appearance is similar to what it might look like if someone colored the product by using a permanent marker, and then with use the marker wore/smeared away. The affected products are from different batches and timeframes. We have not been able to learn anything helpful from the customers.
We have received some of the products back, and the coating thickness, dye stain test, etc. all test as acceptable, so it seems to us like the anodizing was done properly.
I’m wondering if there are known skin related substances, either natural bodily oils/fluids or common skin products (or ingredients in such products), that are known to do this to dyed anodizing? Any other thoughts on a cause for this?
Thanks!
Kevin Enter
– Cambridge, Ontario
October 31, 2024
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Aluminum How-To You’ll love this book. Finishing.com has sold a thousand copies without a return request 🙂 My guess is, that the shaving cream is somewhat alkaline, and more so than the anodizing, or rather sealing, can cope with. And therefore the dye can be removed over time, due to the pore no longer being sealed, and thus the dye and pore is exposed to the shaving cream. It should be fairly easy to test, either by exposing one of the parts to prolonged exposure to shaving cream (Different variants probably, along a wide price range), or measure the pH of shaving creams to see where they are on the scale, as anything over 9 is an issue. Don’t know whether you did the dye spot test on an area where the dye is now missing (i.e. an old part), or you tested on a fresh spot or on a new part. Anodized parts are not great outside of a fairly neutral spectrum, so anything below 4-5ish and above 9 on the pH scale, is going to cause you trouble. M. Stammerjohann A. To begin with, if I were you I would attach pics of problem which you mentioned despite your good explanation of problem. In my opinion, there are two possible reasons regarding source of problem; 1). Poor sealing quality; insufficient sealing duration or sealing bath chemistry. Despite dye stain test result being good, but that won’t mean everything is ok. Weight loss test is most important test for quality of sealing so weight loss test must be done. Also I advise cold sealing instead of hot one). 2). Anodizing layer (sealed) is resistant to only between ph 4-8.So may be sweat issue effected or trigger of sealing quality time over time. Good luck… ALAATTIN TUNA |
