Letter 5006

Purple Precipitate from EN Stripper

We are an EN shop. We were stripping nickel from a large 4140 substrate. The result was a purple precipitate that seems like it's baked into the substrate now. We have never seen such a phenomenon. We suspect that parts, done previously in the same stripper, with some black oxide film on them may be the culprit. Would anyone have any suggestions as to what it is and how it was caused? As well as how to remove it? Yours truly

Austin Hirtle
- Mississauga, ON CAN

Sorry, this is a new one on me as well, Austin. If you have a scrap test part, you might try dipping it in chromic acid. For reasons that I don't fully understand, it seems to have some ability to remove stains from aluminum.

Ted Mooney, P.E.
finishing.com
Brick, New Jersey

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