Folks keep calling this thin layer of case hardening color "stuff" an oxide, but I have never seen an actual chemical analysis of what it really is. I seriously doubt if it is an oxide. If you think about it, the colors you get seem to depend upon the composition of the pack which is mainly carbon. But it isn't pure carbon, or practitioners of the art would use as pure a carbon as possible, such as lampblack. Instead, they use secret or not-so-secret concoctions of bone charcoal, wood charcoal, charred leather, etc., so obviously, other elements are present in the pack, which is heated in a very oxygen deficient crucible. In fact, it appears that a longer exposure to the air during the dump from the crucible to the quench results in less vivid colors. And it is reported that the addition of a little potassium cyanide to the pack provides a greater range of colors. The Marlin Forum has a lot of great information on the process. But like any other internet source, I'd say that some of the information is myth and hearsay provided by folks who are too proud to admit there is a lot we still don't know.
http://www.marlin-collectors.com/forum/v...ae6aae3b599c144Whatever this stuff is, we all know that it fades, because we've all seen faded case colors, and many try to do all they can to prevent such fading. But some guys don't like the looks of bright fresh case colors, and they will use an abrasive compound like Flitz to mute them somewhat. So we know for sure that fine abrasives can fade them. We also know that skin contact over time causes thinning or fading. This is most likely a combination of acidic or salty perspiration, and abrasive dirt and dust on the skin. I've also heard the anecdotal evidence that sunlight or UV light can fade the colors, yet the debate continues. Too bad someone like Turnbull didn't take several equal colored pieces about 30 years ago and keep one in the dark while exposing the others to various wavelengths and intensities of light to finally settle this question. I still marvel at how strong and vibrant the case colors are on my flintlock deer rifle despite the age and amount of use. I have never applied any sort of coating or wax other than a wipe of gun oil, but I also mainly use this gun in very cold and typically overcast weather. It has certainly been exposed to black powder residue, snow, and rain many times, but never to perspiration.
And to answer the question of whether oxides can oxidize, the answer is yes. We know this because that is what happens when bluing, which is an oxide of iron, turns brown or patina color. In that instance, the black colored ferro-ferric oxide which give our bluing its' color slowly turns to hydrated ferric oxide, Fe2O3.nH2O, also known as common red rust.
