Notes From A Jeweler's Bench

Soldering is as much a matter of science as it is of art. All temperature refers to really is how excited molecules and particles are. The use of the appropriate flame is critical but not something a bench jeweler has the time or need to calibrate exactly. Instead it's done more by context and feel. A light brushing flame will produce different results than a tight, sharp flame. Even then, the fuel to oxygen ratio is a matter of feel as similar flame shapes can have vastly different temperatures. Additionally, the aperture of a torch tip affects flame temperature. What works for silver soldering won't work for 14k or platinum soldering.
The lesson here is to realize that a jeweler about to put heat to a piece has put all of this into account before even picking up their torch. The more experienced the jeweler, the more the jeweler knows what they can get away with and what they can't.