The colour in the video was the soap burning off. The soap turns black at 400 deg. C
The myth about burning the zinc out of the brass at even a full annealing temperature of 600 deg C is just that, an oft repeated internet myth. If you consider that silver soldering of brass takes place at an orange heat of around 800 and is held for much longer and that brass and bronze are frequently cast where they are taken to melting point. If burning zinc out of the alloy were true we would always end up with pure copper after any hot work. The few atoms on the surface oxide layer and other contamination of the surface is most likely the element that reacts with the flame.
The varying timings in the video were done deliberately to show the consistency of temperature achieved by the soap system irrespective of where they were held in the flame and how long it took.
It was demonstrated precisely to show how likely you were to achieve different hardness outcomes if you just used counting as your temperature gauge.
Have a look through the thread where I first suggested the system. There is an experiment comparing the soap and the Tempilaq. The advantage of the soap is that you have a progression of colour from beige to black when it achieves 400. Tempilaq has a much narrower band.
I have been exploring the subject of cartridge case annealing...well more accurately it is Stress Relief rather then full Annealing temperatures that most reloaders advocate for cartridge case necks. Full annealing of brass (not cartridge cases) when you are working it in the workshop, is...
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The advantage of the soap over a timed system is that you have a temperature tell tale on each case and it also eliminates efficiency creep.
There is a considerable difference in temperature in the different parts of a propane torch flame. If you count the 6 and have held it in a cooler part of the flame you will risk only taking it to the heat in the middle of the very variable hardness out come.
The video shows that even if holding it in different parts of the flame using soap you can still be sure to achieve the same temperature. That was the point.
The resulting hardness from a given temperature between 250 and 350 varies tremendously depending on the initial stress/hardness condition of the metal. You do need to achieve the 400 C to benefit from the levelling of the resulting hardness.
By using time to gauge a temperature especially by counting, and hand held in a flame you are introducing unnecessary variables.
I just thought it more logical to gauge temperature with a temperature gauge (!) and the soap system gives you that cheaply and effectively.
Alan
