Quote:
Originally Posted by Brian Dudley
Odd... as I recall, nearly every parker I have had re-cased has had it.
Yes, it is dependent on the case hardening process. But more a function of how the trigger plate is machined. The channel in the plate for the unhooking slide results in a dramatically different thickenss of material up the middle of the plate. This is really the main reason for a difference in the appearance and patterning of the colors in that area.
And I will add that not all original examples are that pronounced. Every gun is different.
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Brian is correct in that the inside of the floorplate is machined such that there are three areas of mass; the outside two the same and the center, much thinner. See my work of art below.
The outside square represents the packing box. Surrounding the part is the packing media, which is an organic mixture of the makers own recipe. The drawing shows a theoretical cross section.
There are three factors involved: Random, Variable, and Fixed.
The Fixed factor is the part being heat treated.
The variable factors are Time and Temperature
The Random factor, almost entirely human, is the location of the part, in relation to the inside walls of the packing box, location of any other parts also in the box, and the density of the packing material.
The entire part is held sufficiently long enough for the core of all sections to reach the same temperature.
The quench process is where the magic occurs because the three areas of mass are cooling (from the center outwards) and while the quench media is still working at cooling A & C, B has gotten as low as the quench media will allow. Everything started at the same temperature, was ultimately soaked at the same temp, and eventually back down to the same temp. However, the rates at which they rose, and cooled was controlled by their mass.