Color Case Hardening

by Jim Green, Gunsmith on January 13, 2011

Many years ago guns used to have their non critical parts made of hard iron or even mild steel with a low carbon content. A method the gun companies used to make the softer metals hard enough to withstand the pressures generated by firing was to harden the parts with a method known as case hardening. The outer few thousandths of the part becomes slick like glass and extremely hardened, while the core of the part retains the flexibility needed to keep the part from breaking like the aforementioned glass.

The process can be as complicated or as siimple as you want to make it….. many ” formulas ” exist in the old books I read. But I like to keep things simple…….

After I polish the parts ( in this case a reciever from an old # 4 Remington Rolling Block rifle ) they are then packed in a crucible with charcoal. They are then placed in the furnace at 1400 degrees for an hour – hour and a half. By using different types of charcoal you can achieve different colors. The color is a side effect of the process. Sometimes by mixing wood or bone charcoal and by varying the temps or time just a little bit, you can get colors from a slightly silver to mottled blues in subtle colors. Other times you can get straw or red colors.

What you’re trying to do is add carbon to the metal that is already low in carbon. The high temps are needed to draw the carbon into the metal.

Once the crucible has been heated for the period of time, you then use steel tongs to dump the contents into a water quench bath. Yep…. this makes a lot of steam and a lot of hissing noise and can be a bit dramatic.

This gun has been done up in regular wood charcoal only. The pictures don’t do the subtle colors justice. They’re a beautiful mottled blue to light gray…. and really show up nicely in natural light. The part is still not finished yet however. At this point the part is as brittle as glass, and will actually shatter if dropped on the floor. So I take the parts home and put them in my oven and bake them at 350 degrees for another hour. I shut the oven off and allow it to cool to room temperature on it’s own. This will draw the temper of the steel out and keep the part from being brittle.

Unfortunately color case hardening isn’t really permanent as far as the clors go. After a while the colors can fade from exposure to Sunlight, time, and handling the gun. To preserve the color finish, I’ll spray Dura Coat clear on the gun to protect the finish.

This project will see the barrel get a new blued finish. I will use an old method known as rust bluing, where an acid etches the metal and rusts it to form the dark blue finish. This type of finish is longer wearing than factory finishes of today, and actually prevents the metal from further rusting. It produces an almost translucent finish that is deep in the metal. It’s expensive and time consuming but looks much better on an old restoration instead of the newer caustic hot tank method of bluing you see on modern guns.

This gun was chambered for .32 rimfire ammo, which is no longer available. As the project goes on, I’ll be re drilling the block and converting the gun to .32 Short Colt ammo. The screws and pins will get a peacock color known as nitre bluing. But — more about that later…..

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{ 3 comments… read them below or add one }

mikerosss May 21, 2011 at 10:49 AM

Do you people have a facebook fan page? I looked for one on twitter but could not discover one, I would really like to become a fan!

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Jim Green, Gunsmith May 21, 2011 at 10:53 AM

You can reach our Facebook page here and our Twitter here. Thanks for visiting the website!

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Damon Dickerson January 20, 2012 at 5:22 AM

Hi, I was wondering what you would charge to color case harden some parts for me. They would be disassembled and polished ready to go. I would have a muzzleloading boxlock, hammer,hawkins style trigger guard, butt plate, and barrel band. if your curious you can see this action on a website “pecatonica river longrifle supply”….its called an allen box lock. thanks, Damon

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