I use metholated spirits, otherwise known as denatured alcohol or that stuff
the locals drink....

Works well from a cheap squirt bottle sprayed at the cutting tip. It
certainly keeps the tip cool and stops it from trying to weld itself to the
job in the lathe. Gives a nice clean cut and there is no oily residue at the
end of the job.

The aluminium samples are then tested chemically on a spectrometer and the
alcohol coolant has no effect on the results after allowing the sample to
drip dry.

Hope this helps,
Peter