doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Composition of Case Hardening Colors?

I know the thin case is carbeurized steel, but what exactly causes the colors? And what, besides handling and wear causes them to fade?

I ask this because I just bought a Lefever H grade 12 ga. The gun is a small frame twist barreled model that weighs only 6lbs. 10 oz. with 28" barrels. It looks like it was very well cared for over most of it's life. It has way above average original condition, and the case colors in hidden areas are vibrant and at least 90%. However, it appears it was neglected or stored in a humid area in recent years. It did come from Georgia. There is a thin patina that has turned the barrels brown/black and has obscured much of the twist pattern. This patination is so fine that the metal almost looks as if it was sprayed with a thin coat of walnut stain. A similar thin patina covers the action and sideplates, but you can actually still see the mottling of a lot of case colors under the translucent patina.

I think I could possibly boil the barrels, card, and etch to reconvert the patina on the barrels to black and white without refinishing. The original black and white is still very evident under the forearm wood. But is there any way to remove the patina that is obscuring the case colors without also removing the colors?

Kieth I can't give you a scientific answer about what chemical process causes the various colors when steel is case hardened. I have however had good results bringing back rust blued barrels that have rusted as you describe simply by lightly carding off the patina with 0000 steel wool soaked in light machine oil. It might be worth a try and surely wont hurt anything.

Barrels are not case-hardened, but blued or rust-blackened. This is very different than the colors one sees on case-hardened receivers.

In real case hardening as one finds on receivers, a transparent film is created on the surface. This film has a varying refractive index and thickness and the colors one sees is the result of interference of light as it passes thru the film and is reflected out again. This is the same physical reason why "coated" camera lenses appear to be blue in reflected light; others orange. The coatings themselves are transparent but have different refractive indices.

In principle it is the same as the colors one sees in a rain-puddle that has a drop of oil spreading over the surface. These are known as Newton's rings.

Case coloring is the result of optical interference. It is NOT a pigment color - the layer is way too thin to be pigment-based color.

The transparent layers are very thin - measured in Angstroms. This is why they are so delicate.

If one used monochromatic light the perceived colors would tell you the thickness of the layer.

Keith,
The colors on the barrels are Ferric Oxide that have been converted to Ferro Oxide and the darker colors maybe some logwood that they were initially boiled in.THAT IS NOT COLOR CASE HARDENING ON THE BARRELS , ONLY ON THE ACTION PARTS.
HOWEVER, DO NOT MESS WITH THE BARRELS other than taking some 0000 steel wool and oil and cleaning them. This will likely bring a lot of the colors back.

I know that the barrels were originally rust blued and that's why I considered just boiling them to reconvert the ferric oxide back to ferro-ferric oxide. I wonder if purists would even consider that a refinish since all I would be doing is converting the original black oxide back to black again by the boiling. I do think that I'd need to etch them in ferric chloride solution after carding to bring out the twist pattern because the patina is darker on the barrels than it is on the frame, sideplates, and other case hardened parts.

But the big problem that remains is how to remove the patina from the case hardened surfaces without removing any colors that are still hiding underneath. If Tony was still with us, I might ask him to case color some polished pieces of mild steel so I could allow them to become stained with light rusting, and then experiment with ways to remove only the staining.

Some of the "patina" on the case hardened bits could just be oil, dirt, and crud. Have you tried wiping with something like CLP, then progressing to mineral spirits, alcohol, lacquer thinner, and acetone? Keep solvents off the wood, but solvents should not harm the case hardening or the associated colors. It is possible that the metal was coated with something to protect the case coloring, perhaps linseed oil or lacquer. Both of those will get darker with age and the linseed oil can have a tendency to hold surface dirt.

Some old threads here and elsewhere have suggested polishes like Flitz to clean CCH surfaces, but I don't think I'd risk it without a test on an old beater.

You might also try a stainless steel scouring pad with oil to gently clean the CCH surfaces. I have used it with some success on lightly rusted blued and CCH surfaces.

What about using copper wool (and oil) instead of steel wool? Seems to me like the softer copper wool would remove crud on the CCH or unwanted patina on the barrels without disturbing the desireable finishes.

All that I've done so far is to wipe the metal parts down with Ballistol. Some light rubbing with Ballistol on brown paper towel really didn't bring up any dirt or crud. As I said, the gun is really clean and appeared to have been little used and well taken care of until relatively recently. It also doesn't appear to have been coated with lacquer or linseed or anything to protect the case colors. I can try a little lacquer thinner on a sideplate, but I don't think there is anything there that will dissolve in solvent.

I have cleaned numerous guns in the past that had similar or worse patina using 0000 steel wool and oil or WD-40. Any colors that were hiding under the patina were either removed or left very faint like dark patches. But on those guns, the colors on the water table or inside the forearm iron were also mostly gone. I'm less inclined to do any hard rubbing on this one because I suspect there is a lot more that is worth trying to save. I'm wondering if the electrolysis method of rust removal would take away the patina and leave any case colors unharmed. These seem to be uncharted waters.

I never heard of the copper wool that Dave in Maine mentions. Sounds like something I'd like to try. I have used bronze wool in the past, but I haven't seen that for years either. Many thanks to all who have replied.

The copper being softer than the steel will transfer to the steel and you will get a yellow tinge to the steel.

Keith,
I think the case colors are very similar to rust...an oxide. Chemical rust removers would likely remove the colors as well.