doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Sunlight and case colors

The sage of modern day case hardening, Oscar Gaddy, wrote a series of two articles long ago that were published in the DGJ. I have them both and have read them many times. One of the things I remember most vividly is the electron microscope pictures of the surface of a color case-hardened surface.

That picture shows physical irregularities that are in the shape of tiny prisms which refract light in ways that cause the human eyes to see various colors.

I can completely understand how physical wear can affect those tiny prisms and cause them to not refract light the way they did when new, thusly affecting the colors we see. But, I have yet to be able to understand how sunlight could reshape those tiny prisms. We are told regularly that direct sunlight can do this, and that we should keep color case-hardened guns out of direct sunlight as much as possible. I even practice this myself, just to be safe.

My question is this ........ what PROOF exists that sunlight can do this? And, if proof actually exists, has it ever been explained how that happens?

There is no proof. It does not happen.

I had a 16 gauge Charlin re-case colored by Doug Turnbull. At that time Doug told me that case colors were oxides of organic compounds and subject to fading in sunlight.

I had no reason to doubt him, and didn’t ask for any proof.

I sold the gun to a friend, a serious sliding breech collector, who has kept the gun in a safe since the day he got it, maybe 25 years ago. I was startled how nice the colors still looked when I helped him move the safe to a different part of his house.

I have no proof, just what the guy who does if for a living told me, and what I have seen.

Best,
Ted

Sunlight can provide the energy to form iron oxides. If oxides form on a case colored surface, that were not there before, it is reasonable to expect, that surface will reflect light differently.

How can that happen, Craig? I can understand oxygen, moisture, and heat accelerating the oxide forming process. But, how can merely sunlight do it? I need to understand the process if I am to accept it. Not saying I can't. Just saying I do not have the information needed to do so at this time.

I am the original skeptic .......... sorry.

Stan, a while back I was curious about this subject and went down the internet rabbit hole looking for the same answers you are.

I found dozens of claims that sunlight degrades case hardening colors over time. And I also found many people saying that sunlight has no effect whatsoever. However, I found no credible tests to determine if the claims of fading due to sunlight have any basis in fact. Naturally, I checked Doug Turnbull's website to see if he had any insights, and he didn't address it there. So it was interesting to see Ted say Turnbull does have an opinion. I did find some guys who claim they do bone charcoal case hardening that did say sunlight may fade the colors over time, but none of them showed any proof. I'm not sure how valid testing could be done since samples exposed to weather would oxidize, and window glass filters out a lot of UV light.

Since then, I concluded that this claim is probably just another myth that became accepted as fact after being repeated so many times... something like the myths that all Damascus barrels are dangerous to shoot, shiny bores on vintage shotguns means probable honing, or that small bore Ithaca Flues frames are especially prone to cracking.

On the other hand, if the colors we see are at least partially the product of the formation of some iron oxides frozen during the quench into the top couple thousandths of the surface, I could maybe accept that prolonged exposure to very direct sunlight might have at least a minor effect on those colors over time. I say that only because we know that metallic oxides have long been used as pigments for oil paints, stains, and dyes for cloth. All of those things do seem to be subject to fading from sunlight. However, they are not part of the crystalline molecular structure of the surfaces they are applied to as case hardening colors are. For that reason, I have never worried about using my guns with strong case colors on sunny days, and have never worried that I should be covering them with lacquer or anything but the same gun oils I use to protect the blue on my barrels. I avoid wax on case colors because many waxes contain mild abrasives. And I've also assumed that the old guns I have with faded or nearly non-existent case colors got that way because previous owners just didn't care for them properly. I'd be much more concerned about not cleaning and oiling my guns after exposure to rain, snow, perspiration, or even handling case colored surfaces with leather gloves impregnated with abrasive dust or tanning chemicals.

Stan, my point of view is that assumptons have to be made, such as, in open air where sunlight is available, it is reasonable to believe that oxygen and water in the form of humidity, are also available. The quote above, strips it down even further to exclude firearms case coloring?

Anecdotally, some folks try to retain "patina", which may be at least in part due to oxide formation, because it looks, reflects light, differently than a new finish? Sometimes, one might look under a stock or other part for a closer look at how original colors might have looked? Is every external case colored gun surface subject to "pyramid" wear, maybe?

I also choose the term reflect, over refract, regardless, some skepticism is healthy, but absolutes such as in the quote, have the backing of proof?

I remember Dr. Gaddy discussing a test he did. He made two rectangular pieces of steel, then color case hardened them. He put one piece in a window sill and the other in a drawer or similar. After an extended period of time, he put them side by side. There was no difference in color.

I remember the same. This was pretty much the definitive answer.

Craig, yes, but to my way of thinking oxygen and humidity (moisture/water) can also present in the absence of sunlight, can they not? And, oxidation can and does happen in the dark, if oxygen and water are present. So, what does the sunlight add?

To wit, even though a forend iron has been devoid of nearly all light, under the barrels, and sustains high levels of case color, it was never deprived of oxygen and moisture, except ............. by a light coating of rust preventative oil. Had the oil not been present as a moisture barrier the oxides would have formed anyway, without light.

So, back to square one for me; what exactly is it that sunlight itself can do to the surface of case colored steel that can transform the prismatic surfaces?