Ahh thank you those are excellent tips, makes sense the black junk is burned flux. Speaking of tips i also used the big one (it’s a #7 for a gentec jewelers torch if that tells you anything) but i think it generally had way more heat than i needed so I’ll probably switch to my smaller one which i assume will still have more than enough.

also i was just brazing this sitting on a firebrick because i didn’t want to make a fixture. So the heating was not at all even or smooth.

I assume i should be paying close attention also to the color of the steel? Seems like something in the dark red/cherry red range? Definitely went orange sometimes.