If you’re interested in vaporizing pure spice (no added herbs) using a non-reactive metal mesh disc holds spice much better than multiple screens. Heat the disc slightly before putting spice on it, and the spice will melt right in.

Use a jet/torch lighter and aim it straight down toward the ceramic diffuser. When I started using the GVG, I inadvertently held the lighter at an angle, and most of the flame was directed toward the glass sidewalls rather than the diffuser.