Flame Annealing

The annealing of glass by a torch flame. It is done by gentle heating of glass, right below its softening point, and letting it "soak" at that temperature for a couple minutes and allowing it to cool slowly.

Edited to add; Read Brian's excellent explanation, it's post #4 in this thread; [1]

If I need to make several pieces for the final item, what I do is flame anneal the various components and put them between two pieces of ceramic fibre blanket until I'm ready to assemble them.

By flame annealing I mean turn the oxygen way down to give a big bushy yellow flame and 'paint' the worked item with the flame until it is covered with soot.

While the workpiece is too hot, soot won't settle on it.

As it cools, soot settles on it and I keep it moving in the flame for a while until I think the core temperature is the same as the skin.

When I'm ready to add components to the final piece, again I turn down the oxy and warm it up in a big bushy yellow flame. This deposits soot on the workpiece but as it gets warmer, turn up the oxygen gradually. When the soot vanishes, the pieces are at the correct temperature and ready for work.