If you hate the smell of coventional coolant and the fact that it makes thing rust,go synthetic.
I was using Rustlick until recently.Nothing rusts and it smells great,butI have been turning brass in great quantity lately and discoverd that it reacts with the brass.
It turns a nasty greenish colour and leaves streakes all over the machine.Takes hours to clean up the mess.
I am now trying Cincinatie millacron which in the mixing barrel looks alot like coffe with a touch of milk in it..........Scary at first but looks whiteish when in use,smells neutral and
for now is working well with T6 as well as metal.
I have mixed brass shavings and the new coolant in a cup 3 days ago and all seems well so far.
Syth. is more expensive but so are cnc machines!The previous owner used regular coolant in my cnc lathe and it cost me big $$$ to have the hydraulic cylinders reground and built up again,not to mention the seals from England and the time it all took.
As a result I chucked the balance of the 5 gal. regular water soluble crap I had left over.
Should you not be convinced from my experience....Use a refractometer often to check your juices!
Best of luck