To close a matte tap hole a clay plug is fastened onto the end of a dolly bar and lightly hammered into the open hole using a rapid and very precise tapping technique after which the material itself quickly hardens inside the hole to form a very secure plug that must be burned out to open the hole again. If the dolly bar is struck too hard or improperly once the plug is seated the plug will quickly fail. That is why a second prepared dolly bar is always close at hand.