There is an interesting AI point here: the US Copyright Office recently tried to argue that images generated by a model could not be copyrighted, no matter how detailed the prompt nor how curated, because the artist did not envision the exact output and thus it is merely the output of an uncreative mechanical process. Clearly OP does not envision the exact way in which glass will shatter or frost or crack, and has to repeatedly update and revise based on what happens; are his glass portraits mere mechanical outputs and uncopyrightable?