You can turn one rune into thousands given enough time.
Make sure that you have ONLY one rune in your inventory. Go right in front of the Combo Master. Press F9 to quick save. Talk to the Combo Master, and go to the exchange menu. Put your rune up in the one of the 4 green open spaces. Press F8 WITHOUT closing the menu to quick load. The one you started out with will be back in your inventory, and now you can pull the new one down beside your old one.(1=2,2=4,4=8,then its plus 4 each time after that)
If you have one from the wrong class that you dont want no sweat. turn one into 4 or 8 then trade'em in. When you trade them in, the others that you duplicated will go invisable but the squares will still highlighted blue. Don't worry you can still use them, but do not save until you,ve used them. If they go red you just lost them.