I have been weathering trains for over 50 years and I can honestly say FLOQUIL is the BEST PAINT EVER.
It is Acrylic/Enamal formula spays on in a SUPER FINE MISTY light dusty coat.  
ALL water base paints goes on clumpy and orange peal globs, no matter how much you thin it down.  This is due to the surface tension nature of WATER that it is made out of.  FLOQUIL drys in a FLAT surface finish, perfect for WEATHERING. 
I know the price seems high, that is because for the last 10 years i have been searching Hobby shops for Floquil paint,  and its ALL GONE.  You cant find Floquil anywhere.  No more is being made or available.  The company went out of business 10 years ago.  And now Testors model paint company is out of business also.
I can weather 50 cars with 1 bottle, using batch method.  That makes it less than $1 per car.
I recommend stocking up now, before it is COMPLETELY GONE.
note: marine colors paint is the exact same formula as railroad colors.
I use laquer thinner for thinning and cleaning air brush.
i like using a few BB's or lead or steel shot inside bottle during shaking process, then just leave in bottle.
note: numbers and names in alphabetical order

These paints were stored in the Distributors basement and had never made it to the hobby store. They are BRAND NEW and FACTORY SEALED.  The manufacturer has gone out of business between 5 and 25 years ago.  They will never be produced again.  the only ones available are those manufactured years ago.