The challenge with a pot melt is that even you do put a sheet of clear underneath, the flowing glass pushes it outward. In a screen melt the glass is dripping straight down from all manner of sources…so your clear stays more in place. I haven’t used shelf paper under the pot melts because it would just get picked up and carried along and now I have ick that I can’t sandblast away. Oh the trials and errors, I have experimented extensively with pot melts because I love the look but sometimes I just shake my head and wonder why I was so optimistic that something would work! LOL! The disappointments can be very informative.