Funny,... I tried that too and had the same problems,...Then I went k.i.s.s. and tried to mix a simple 2 part mix,... I have the same liquitex products sitting on my shelf,...full . I think the whites and yellows have the largest particles,....I know right!?! As for the future thru an airbrush ,...I still have not figured that one out yet,... by retarder you mean, what,...water, alcohol,...?