I've used both sand and glass beads and the glass beads is the only way to go, it gives you a nice clean prepped finish to the metal that takes the browning acid great, the sand on the other hand made for a very rough finish when all was said and done. I'm in the process of putting together a GPR flint kit and when I get ready to brown the metal I will take it over to a local diesel shop that a friend of mine works at and use their bead blaster cabinet. Bead blasting, if you can do it, will clean the metal better than any cleaning method I have seen, once it's blasted I wrap the parts in clean paper towels while still in the cabinet, then never touch them with my bare hands again. Some folks use rubber gloves but I prefer clean cotton knit gloves. The browning solution I've used in the past and will use on this one, if it still works, is an acid solution made up for Green River Rifle Works in Roosevelt, Utah, but a chemist that had a business in Roosevelt serving the oil industry, it is some of the best browning I have ever seen when the metal is perfectly clean.