Annealing: Furnace or Torch?
Annealing doesn’t mean “to soften”. It simply means to alter the physical or chemical structure of something using heat. There are many characteristics of brass, “hardness” is just one of them. There is also strength, toughness, and the most important one for horn makers “ductility”.
Hardness is just a materials resistance to abrasion which is actually not all that helpful in bending. Ductility on the other hand is how much a material can be bent or deformed without failing. Softer tube alone is not easier to bend, but a more ductile tube is. As it happens, there is a correlation between a brass tube’s softness, toughness, and ductility; the softer the tube, the higher the ductility.
HOWEVER, the rate of change of each of these properties is not the same. In other words it is possible to heat a tube in such a way as to increase the ductility more than the correlating softness. You can in fact have a tough(ish) hard(ish) tube that is ductile enough to bend.
A maker that anneals with a torch has no control over the individual properties. The only way to do this is with a controlled furnace. Some makers claim their annealing temperature is whatever F based on the color that it glows, but that’s like baking a cupcake to an internal temperature of 185 (proper cupcake temperature) with a 3500 degree oven. Even if you take out the cupcake at the exact moment it reaches 185 (and it wont take long to overheat), the outside of the cupcake is likely burned to a crisp.
While tube can be annealed for bending using a torch (sometimes called “flash annealing”), the properties of the brass afterwards are rather rough. Flash annealing often destroys a tubes toughness and bends can oval and wrinkle, especially around tighter corners. Proper annealing procedures create a nice ductile tube that is stiff enough to hold its shape and integrity as it’s being bent.
While torch annealing is the traditional method of annealing tube, much higher degrees of accuracy are possible through the use of a furnace.