When i do this, i mix the gold(or whatever color) dust, with vodka and paint the edges with a small flat brush.
Or a script brush...very fine lines with one of those. http://www.artistpaintbrush.com/images_royal/2/langnickel_royal_knight_script_artist_paint_brush-l7585-0.jpg
I like metallic gold airbrush color on the very edge of a small foam eye shadow applicator.
thanks so much for the advice! xx