Pastel wash blues

yes, what Doog said.

I grind pastels then mix with acrylic hobby paint washes for this effect.

mix = (acrylic paint + water + liquid dish soap + pastel powder grind) 

ratio of the mixture is determined by the thickness you want to achieve. Play around with your mixture on a pallet until you get the viscocity you're looking for

i have streaked weathering powders with water (when i accidently spit on it) but there are too many liquids out there. and especially for pastels you need a flat finish. they will not stick to gloss. try artist oils. i just did my first pin wash and filter abd i can't wait to have another vehicle painted to try it again. i ahven't been this excited about an aspect of modeling since using silly putty for masking. thanks to doog for urging me to try it. MICHAELS has them 40% off this week.

I wouldn't use a wash with pastels. It's doubtful that you can grind the finely enough to make it an effective medium in liquid.

I'd use a regular acrylic wash with a dab of dishwashing liquid to help dispersion, and the do a simple dusting of pastels. You can even just try the dusting first, but you may have a problem with the pastels eventually coming off. That's why pigments were made for modeling--they have much, much better adhesion properties and can be effectively fixed with either mineral spirits of pigment fixer. You'd be better off to spare yoursel the headaches and just go in for a bottle of pigments--they're well worth the investment.