Dear Editor,  I am having problems with my MWF staining the parts I make in my VMC.  I only make part from QC-7 aluminum.  I have been having trouble with this for over a year now.  I have had may different brands a coolant in my machines, each time I would remove the old coolant and clean the machine and put new coolant in.  Each time now with the same result.  I use DI water with oil based or synthetic, I have sent countless samples to many labs and they all say everything is normal.  I get a kind of  hazy film all over my part.  In the past the film would not start to appear for about a month, then I would change the MWF.  It would go away for awhile and then come back.  I changed the coolant yesterday and today I have stains.  Surface finish is the most important part of the parts I make and the stains make the parts worthless.  Some jobs I run have cycle time over 200 hours.  This is a real big problem.  I have contacted every company I have gotten coolant from and they put in additives try and help.  Nothing ever has.  I am at a loss.  Have you ever heard of this problem when machining QC-7 aluminum?  Any information you can offer would be great.  Thank-you in advance, JM