In reply to phja:
In all honesty, if you want that 'milky' effect then I would suggest a 'Big stopper' (Google it) which is a 10X ND filter that can be used for both colour and B&W photography. They are great (I have one).
The only drawback is you need the filter holder etc and the 10X filter itself will set you back best part of £100 AND..... it's made of glass !! so no dropping it
The one I have is made by LEE filters, but you may be able to find a cheaper alternative ??
Good luck, you can get some great effects with it
JH.