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Tarnish and finger prints on machined copper

In the past I have received these copper parts before and I processed them with turgitol, ipa/ acetone power washed after each step then a bright dip in 20% nitric acid for 30 seconds. The parts came out pristine I could not have asked for anything better. Now I am receiving more and more of these parts they are coming with hand prints and tarnish is there anything I can do with out setting up a tank line. My thought was that oils or cooling fluid is being sucked into the part from the machining process and I would have to bring the part up to or over the temp. created during that process then start like I had previously. any help or hints would be greatly appreciated.
thank you,

Glenn Thibeault
- Southbridge, Massachusetts, USA
2006

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Hello Glenn,
The tarnish and fingerprints on the copper should be removable with a mild microetch, or a heated acid cleaner. It would be much easier and cost effective on your part if you could contact the machinist and ask them if there is anything they can do to reduce the fingerprints. It sounds like there was a time when you were getting cleaner parts to work with, correct? As you probably know the 20% nitric acid dip is less effective operating with copper concentrations above pre-determined limits. The fingerprints and oxidation are below the surface you are currently "etching back". A good acid soak cleaner has the ability to draw soils out, nitric acid has limitations. Good Luck!

Mark Baker
Process Engineer - Syracuse, New York
2006