On Wed, 01 Feb 2006 19:13:17 GMT, Why wrote:

http://www.sunnysidecorp.com/metal_working_oils.htm

Sulfur.

This additive performs an anti-wear function in cutting oils by forming
a chemical bond between the cutting tool and work piece, thereby keeping
the tool from coming in direct contact with the metal being cut. There
are two types of sulfur additives, active and inactive. The inactive
compound is used for cutting mild (low-carbon) steels and will not stain
these softer materials. The active sulfur forms a stronger bond than
the inactive but will stain soft metals.

BS, It will only stain soft metals like brass which I have been
running by the 1,000's for 30 yrs "IF" you don't wash the days run
in Naptha! Don't wait 2 days.

I think that's a chemical reaction between the Copper & the "free" Sulfur.
And a soap should work as well (or better & cheaper) for washing IF
you can legally/properly dispose of the wastewater (which might be more
likely with a biodegradable water-based cutting fluid).
--
Cliff