Actually, I noticed that it sort of looked like that. If anyone’s curious, that flesh-coloured bit is my hand holding the webcam.
Alcohol, methyl, wthyl or isopropyl, can leave soot too.
Indeed, any fuel containing carbon can, even normally clean-burning methane. It all depends on combustion efficiency (or the lack thereof). Generally, if there’s an orange-ish flame, you’ll get sooting.
Since I’m sure you’ve all been biting your lips waiting to discover what my solution was, I’ll tell you. I found some odourless lamp-oil and it works like a charm. Thanks, everyone!