You are the one melting your hands, by your conscious and unconscious interpretation of your astral body. Remember that your hand is a representation of your physical form, so you don't really have a hand, you assume a body because you perceive yourself as the person you are in the waking world, in a world of energy forming a body. It may from time to time be distorted.

Try experimenting;

The astral world and the astral body is comprised of thought and feeling. Mentally see and will your hand into what you want it to be. From my experience some astral planes, or layers are easier than others. I made my hand melt and re-materialize, it was interesting studying the science of the astral body and the astral world.