How do I get a pickeled effect on Mdf?

if you want any wood grain to show through the white wash, you'll have
to faux-grain it first. the "pickle" is just thinned paint.

I have used the Minwax Pastels Winter White quite a lot on Oak for that
80's white washed look that was so popular. It is an Oil based product
which is probably better than water based for MDF. It works great on
Oak. You can control how white things look by how much you wipe off. It
really does just seem like watered down white, oil based paint. I find
it real easy to work with.