I've heard that the old-time coolant/lubricant of choice for copper was...milk. I assume modern chemistry has come up with all sorts of custom compounds for the purpose since those days, but it might be worth a try. I assume you'd want whole milk, not skim.
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Don't believe everything you know. -- Bumper sticker
Everybody is ignorant, only on different subjects. -- Will Rogers
There are lots of people who mistake their imagination for their memory. - Josh Billings
Law of Logical Argument - Anything is possible if you don't know what you are talking about.