Since I've never done racking on a large piece I don't know translatable my experience is with raking in lampwork.
With lampwork beads-making, I do a LOT of raking in my designs. On the bead, the most effective way to control raking is when the surface of the bead is warmer than the core but not soupy hot. I find that my most controlled raked designs is when I pick up a teensy smidge of glass from one end of the piece and I carry that up to the other end without allowing the glass to "dam" behind the raking tool. Does that make sense?
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With lampwork beads-making, I do a LOT of raking in my designs. On the bead, the most effective way to control raking is when the surface of the bead is warmer than the core but not soupy hot. I find that my most controlled raked designs is when I pick up a teensy smidge of glass from one end of the piece and I carry that up to the other end without allowing the glass to "dam" behind the raking tool. Does that make sense?
Here is an example of a racked bead using the minimalist technique:
http://pics.livejournal.com/khalja/pic/00057bqg/g39