You'll have *better* luck with propane if you buy a *new* empty tank (try a hardware store) & get it filled at a filling station--don't use a "swap" place--that's a great way to get a tank that's been left out in someone's back yard, etc.
Then when you need more, take it to be filled & make sure you ask them to "purge" the tank before re-filling it--that way you won't get a build up of the nasty crap that settles out of the propane (the "smelly oil" & stuff they put in it for safety, etc) at the bottom of the tank...which will give you better results.
My tank still looks close to "new" (the "new tank wrapper" finally fell off this year
) after several years--as opposed to tanks I've seen in the "swap cages" that have rust, ick, etc--you're never 100% sure if those are *really* purged between fills, etc. (they're only as good as the kid who does the fill....)
Then, turn your torch down & work further out....seriously--you're likely trying to "rush" the glass--you want it to be "faster" & "hotter" & that's something the hothead just *can't* be--when you try to make it be something it can't, you get soot! (and you'll do it without even realizing it--it just happens!)
And I'll agree with the "get a cricket" crowd--much, much, much nicer than a minor, you can adjust it with such tiny tiny adjustments it's amazing! I
my cricket!!