Fuming shows up against dark colors or blacks much better than lighter colors or clear. When you go ahead a fume a dark piece of glass, the effects of the fuming automatically show up. This is for artists who want their piece to show the fuming effects right off the bat, instead of having to get the piece dirty to show the fuming effects. This would be done for any pipe that may not get dirty like a dab rig or pendant.
Fumed on cobalt blue glass
Fumed on clear glass