I have Copics, but I like to use Sharpies or Bics to color rhinestones; the Copics leave a gummy, sticky feel. But I like the idea of coating them. I use Diamond Glaze or Glossy Accents, and found the neatest idea on You Tube: I cleaned an old nail polish bottle very well, and poured Diamond Glaze into it. The best part? The brush is ready, and when you're finished, goes right back into the bottle. I ruined a couple of my good paint brushes when I forgot to clean the Diamond Glaze from them.
And not that this happened to me (lol)... but clean your nail polish bottle very well. I had some clear top coat, must not have gotten all of it out before I poured the Diamond Glaze into the bottle. When I tried to brush the DG onto paper beads, the glaze had thickened and wouldn't spread; some of the DG had congealed inside the bottle. Had to pour out the DG and start over. This time, I used nail polish remover to completely clean the bottle and the brush, rinsed with warm water; let it dry and started again. Works like a charm!