Went to use my CNC Bridgeport today and found that the soluble cutting fluid had gone grey! No nasty rancid smell, and it hadn't de-emulsified - it's only been in for a matter of maybe 5 weeks, with occassional use cutting aluminium alloys.
The soluble oil is 'Excelfluid LC' from J&L, and I use it in all my machines (manual Bridgeport, 540 Surface Grinder, Cylindrical Grinder etc) - it occassionally goes rancid, and usually de-emulsifies if left unused for a bit but I've never had it go grey. This was a dark 'machine grey' Very odd.
Is it possibly some strange reaction with aluminium alloys?