Bo Nordh used an alcohol lamp or candle. Not recommended for the inexperienced, though.
Hot water is messy, slow, and does indeed turn some vulcanite a lovely, deep shade of olive-puke greenbrown. Not recommended for anyone.
Oven-baked pans of sand or salt are a complete PITA for one stem. Avoid except for mass production.
A paint stripper type hot air gun (on a low setting if adjustable) is the best choice by a considerable margin. Just wear gloves, DO NOT LEAVE FOCUSED ON ONE SPOT, and test the stem for "bendiness" frequently until you get a feel for it.