Devardi is tricky, some colors are awesome, and some, not so much. But your use of the word 'burn' makes me think the issue is less with the glass, and more with where in the flame you are heating it?
I use Devardi glass a lot, but have never burned it. If you are actually burning the glass, I think your working too close to the torch, and need to back out to the middle of the flame. With big rods like that, you have to hear them slowly, true, but also over a wider area, not just the tip, let the bigger part of the flame, wash up the rod, and warm it ahead of time, so when it gets in the flame, it's ready to go..
To make a bigger bead, warm a larger gather on the rod, touch down on the mandrel, and wrap while the glass is staying in the flame. Keep twisting the mandrel as the glass lays down on it. Don't pull the glass off the rod with the mandrel, but let it melt on to it. Once you have a nice amount of glass on the mandrel, put the rod out into the tip of the flame to stay warm, but move the bead into the middle of the flame and even it out. This is where you learn glass and gravity! Spinning the mandrel and using the heat will produce a nice round uniform bead all on its own, ( with practice )
Once you have the shape, let it cool out of the flame a bit to harden up, while moving the rod closer in to start melting again. If the bead isn't big enough, now you can add more glass to your existing bead and make it bigger.
When you have your size right, bring the bead to a light glow, and use the marver. Don't roll the bead back and forth in the track, rather, keep the mandrel in one place, and spin the bead in the track. That is how you get the shape...
Help any? Or did I just confuse you?
