There is something marvelous about glass. It can behave like clay, stone, honey, wax and have a continuum of plasticity by just changing its temperature. I sometimes us a common ‘butter knife’ to move the glass around as well as razor blades, picks, tweezers, pliers. You can use any tool that does not catch fire and does not leave a residue. Graphite is probably the most used substance for sculpting glass. It does not melt and does not leave much of a residue.