An important part of working with glass tubing is being able to anneal the glass after shaping it. This requires a sooty yellow flame, which a blow torch ordinarily doesn't produce. This problem is easily solved by making an adjustable choke for the torch, which restricts airflow into the base of the torch head. The choke itself is a piece of polyethylene rod with a hole drilled through axially, where the internal diameter of the hole matches the external diameter of the torch head. In my case this diameter was exactly half an inch. Teflon probably would have been a better choice of material since the torch head does get hot, but so far the choke has worked well and hasn't melted yet.