Question about heat treat coloring. . .

[BP Green]

Hi guys,

I'd like to make it clear that I am not a knife maker or designer - hell I'm not even very mechanically inclined - but I do have a bit of an artistic streak. I really like the subdued colors heat treated metal takes on. I've seen a lot of knife scales with that treatment and have been entertaining the thought of trying it myself.

Has anyone here ever tried it? Is it difficult to do? Any info would be appreciated. . .

[shakie]

every color designates a specific temperature. starting at about 500* you have wheat going up to purple/blue 800*/900* past that the color goes away. To start again I dip it in muriatic acid (a few seconds) scrub with soapy water, buff on white wheel, scrub again and heat. You have to take into concideration heat rises through the steel so if your heating the bottom, the top is going to get too hot . I would look up heat coloring steel, there's tons of info on the web. Practice practice

[BP Green]

Thanks Shakie. That's great info and beautiful work! You have skills my friend! I'm thinking about starting out on scrap metal just to practice then from there I'll progress ro cheap beater knives. After that maybe I 'll be ready to take on a little more. Thank you for your help. It's much appreciated. . . .

[Zero Gravitas]

The most beautiful colors do end up on scales - the cutting edge needs heat treat thats meant for cutting edges. Check out color case hardening - traditionally done to shotgun, rifle and pistol frames.

[BP Green]

The most beautiful colors do end up on scales - the cutting edge needs heat treat thats meant for cutting edges. Check out color case hardening - traditionally done to shotgun, rifle and pistol frames.

Yep, very familiar with it. I collect vintage guns as well. Gorgeous work on that receiver. Are you familiar with the work of Doug Turnbull?

[shakie]

When you heat treat a blade, you bring up the temp to say 1500f which is past the coloring stages. then you cool it and temper it to 350f-450f-550f depending on what rockwell #s you're looking for. if you clean and polish between HT and tempering you can bring back the color designated to the 350f-450f-550f

[Zero Gravitas]

BP,
Yes to Turnbull, I have Ithaca double (ICD) that was finished by Turnbull both the CCH and the blueing. That photo is from Turnbull.

[S.Shepherd]

Case Hardening

The following is a composite of two excellent posts on case hardening by subscribers Bruce Conner and Ward French.

It can be found at: http://members.aol.com/illinewek/faqs/case.htm

For readers wishing to pursue colour case hardening further, I strongly recommend a series of two articles by Mr. Oscar Gaddy on the subject, found in the winter 1996 and spring 1997 issues of the Double Gun Journal.

Bruce begins:

Case hardening involves putting carbon (or a combination of carbon and nitrogen) into the surface of the steel to make it a high-carbon steel which can be hardened by heat treatment, just as if it were tool steel or any other high carbon steel. Only the outer skin gets hard this way, the center is still tough and malleable. This makes for a strong part with a tough surface.

Ward continues:

Low carbon steel, i.e. steel with about 20 points or less of carbon, cannot be made to harden by heating and quenching, as higher carbon steels can. Low carbon steels are tough, soft and flexible. They wear quickly and batter easily.

Many parts, including gun actions in days gone by, were made with low carbon steel. It was cheap, strong and easy to machine. Unfortunately it would not stand up to the battering of use in the field. Case hardening added carbon to the surface skin of the steel part and left it in a state which could be hardened by quenching.

To case harden a part (the process is also known as pack hardening) the finished low carbon steel part is placed in a sealed container, packed with a high carbon compound. In the old days this was simply animal hide or bone. The container filled with parts and carbon bearing material was brought to a red heat and held at that temperature for a time determined by the size of the part. The time might be from a half hour up to several hours. As the bone or hide became carbon in the container, and a carbon rich gas formed, some of the carbon would infuse into the surface of the steel. Over time this would penetrate several thousandths of an inch, producing a high carbon surface on the low carbon steel part.

At the proper time the container is removed from the furnace and the contents dumped into a quenching bath, usually water with perhaps a surface coat of oil to lessen the shock of the quench. The high carbon surface skin becomes glass hard, but the low carbon body of the piece remains soft and very ductile and able to resist shock. Properly done it made a simple and very durable system for treating metal action parts.

Colors are produced when the steel surface is cooled unevenly, capturing the natural blues, oranges and yellows of cooling steel. Several methods are employed to do this. Stevens moved the parts into the quench in a jerky fashion, producing a barred effect of color. Perazzi did the same. In the London trade the quench bath, usually a barrel with soft water and a skim of oil, was agitated by stirring, or with bubbles of air, producing a mottled effect on the steel.

Bruce adds:

Color case hardening is done much the same way except that generally only leather and bone are used as the carbon source. I don't know why this works better than charcoal, but it does. You get more brilliant colors with them. The other thing you do is modify the quenching bath. You need a source of bubbles. LOTS of bubbles to really rile up the quench bath. Adding a bit of potassium nitrate to the water increases the brilliance of the colors as well, but isn't a requirement. You have to watch the temperature more closely with color case hardening or the colors won't come out well. Don't go over 1350 F.

Kasenit and similar compounds are a lot easier to use and you can just use a torch. You heat the part up red, dunk it into the Kasenit compound and get a good coating of it sticking to the steel in the places you want hardened. Then reheat it up to a good red and quench it in water. This can be repeated to increase the depth of the case hardening. It works very well and is quite fast, but leaves a kind of dull grey color to the surface. For parts that are internal it works great and if you make the hardening deep enough, you can polish the metal and still have a hard surface.

Anyone who has a case colored part should be aware that colors will fade on exposure to direct sunlight over an extended time period. Parts must be protected. Clear fingernail polish or a similar lacquer will protect the surface and a gun case or cabinet will do the rest. Case hardening was widely used on all lock parts except springs, and the process could be carried out even on the frontier with a minimum of equipment and knowledge.

the section I made bold I believe would apply to knives that have been heat colored also.