Mike,
I've read everything I can find about case coloring, which isn't all that much, even in this internet age of information sharing. Understandably, the handful of pros like Turnbull, Brad, and others who make their living at it are going to be reluctant to share the details of their hard earned trade secrets. I also saw an interesting (but short) segment on Galazan's case coloring process on The Outdoor Channel recently, which showed them baking and quenching one of their O/U sidelock frames. But of course they gave only generalized information on the process. (As an aside, they did mention using some chicken bone charcoal in their matrix, which might account for their unique mustard colors).
I haven't had problems with frames, tangs or forends warping. I use some rudimentary bracing with stainless steel nuts and bolts to hold the tangs and sidelock plates at the correct dimensions. I also follow the processes outlined by the late great Dr. Gaddy in his two DGJ articles, which require annealing at 1450 for an hour and allowing to cool slowly over night, and then case coloring at no more than 1350. Following his direction, I then allow the work to cool to 1150 and hold it there for about an hour in the kiln before quenching, but I have quenched as high as 1225 with no problems. I strongly suspect its that last step that people who've had warpage problems don't follow. If they are baking at 1500 (or more according to some internet stories) and dumping directly into an icy quench at that temperature, it would come as no surprise that warping problems will occur. I can't recall where I read it, but one author claimed that there is substantial evidence that the case coloring guys at the old factories would take the crucibles out of the kilns and set them aside to cool for up to an hour before quenching. That's hard to believe, as the work would probably cool down to 500 or less after that much time, and that would seem too cool to form colors when quenched. I have been contemplating cooling down a crucible to a much lower temperature (say 700) before quenching to see what happens, but haven't done so yet.
Also, some people assume that when the part tolerances are noticeably tighter on reassembly, warpage must have occurred. As Dr. Gaddy explained, that is not necessarily what is going on. The case coloring process adds a glass hard layer of carbon into and onto the steel which is measurable in thickness with scientific equipment. This thickening process sometimes requires refitting of parts during assembly. A good example is the rotary barrel locking cam in LC Smiths. I typically have to polish out the frame recess to get it to fit and turn freely after case coloring. I have also had some success filling in tiny pin prick sized pits on frame exteriors by case coloring, believe it or not. And a light coating of top coat lacquer also helps make them undetectable to the touch and eye.
So getting back to the topic, according to the real pros like Dr. Gaddy, warpage is generally the product of quenching at too high a temperature, which is not required to obtain correct case colors. So now I'm curious--when you were having troubles with warpage, 1) did you anneal the work prior to case coloring, and 2) at what temps were you quenching?
Last edited by Justin Julian; 12-29-2011 at 02:14 PM..
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12-25-2011, 09:05 PM
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