It all comes down to proper air/fuel mix.
Soot is a result of an incomplete burn. Either too much fuel, or not enough O2. Smaller holes may yield a better burn.
The "candle" method I've been using has a very small wick at only 1/2" exposed and using 91%. When I started out with 70%, I started with a wick length that long, but it took around 25 minutes to get the water boiling. I lengthened the wick to 3/4", and that got the boil time down to 12 minutes. No soot.
But with 91%, I keep the wick to 1/2" (after trying 3/4" and getting a huge amount of soot), and the boil time is the same 12 minutes, and yet I still get soot. What adjustment could I make to that? It seems that the problem started when going to 91%. Is there a way to increase O2 to an alcohol candle design?
I'll post a pic of what I'm using later after I get a pic taken.
BTW, in doing a little more research, I've been discovering that Isopropyl alcohol is supposedly NOT safe to use indoors! That's a shame since I've done all my experiments with it indoors, including burning 10oz. in a "heater can" for over an hour and a half. I keep hearing from some sources that it's clean and perfectly safe. But check this out:
"No, you should not burn isopropyl alcohol indoors. Isopropyl alcohol is highly flammable and produces hazardous fumes when burned, so it should be used in well-ventilated areas only. Additionally, while isopropyl alcohol is a relatively safe chemical, the vapors and fumes it produces when burned are hazardous, so you should never breathe them in." Can I burn isopropyl alcohol indoors?
What should I make of this?