I'm painting silver dust on gray fondant. I mixed the dust with vodka, but I can see the brush strokes when I paint. I've tried making the 'paint' thicker, but it still looks a little streaky. How do I avoid this?

I'm using a good-quality dust (not Wilton).

Yes, but are you using the actual highlighter stuff, or just metallic dust? Properly mixed, and using the proper stuff, it should look like actual molten silver. And be kinda thick. This is what I use for gold and silver. http://www.nycake.com/images/products/thumb/HighLightsGold.1.1.JPG

Make light coats, let them dry in between then go over it again. If you keep going over the same spot while the dust is stick wet or tacky it will pick it back up.