Color Case Hardening Tutorial (Part 1, tools and equipment)If you want to learn how to do case color hardening, charcoal bluing etc. or want to learn more about how to improve your process, I can’t recommend a better resource than the below listed book. I wish I would have had this book when I first got involved with case color hardening.
Another good resource, and it is free, is the Marlin Firearms Collectors Association
https://www.marlin-collectors.com/forum/viewtopic.php?t=Also, Oscar L. Gaddy "The Color Case-hardening of Firearms", published a 2 part treatise in “The Double Gun Journal” Winter 1986 and Spring 1997 issues.
Below is a photo of the oven I am currently using. It is an old Neycraft 220 volt oven that I purchased from Brownell’s over 30 years ago. It originally came with analog controls. I spent many an hour babysitting this oven, adjusting the thermostat and opening and closing the door to maintain a constant temperature. When the heating element burned out and I had to replace it, I decided while I had the oven disassembled that I would convert it over to a PID controller. I used components from Auber Instruments for the upgrade. Total cost for the controller, heat sink, SSR, and miscellaneous materials was less than $150.00. This was one of the best $150.00 I have ever spent. You just program the controller, and as Ron Popeil would say, “set it and forget it.”
Next are my crucibles. Mine are fairly simple welded boxes made of mild steel. These are bottom dump crucibles that are initially filled from the top. The welded nuts on the sides of the crucibles are for attaching the handles for removing the crucibles from the oven and dumping the contents into the quench. Further on into this tutorial you will see how they work.
Charcoal is used to pack the components in. The charcoal used in traditional case color hardening is a mixture of bone charcoal and wood charcoal. A mixture of 20 to 25% bone to 75 to 80% wood is used. The charcoal at temperature forms a gas shield around the parts so one, they do not scale when heated and two, keeps oxygen from contacting the parts as they travel from the crucible to the quench. With out this shield, you would still obtain hardness, but would not get the colors we desire.
Here is an up-close picture of the charcoal from Brownells. The bone is on the left side of the photo and the wood is on the right.
Color Case Hardening (Part 2, Packing the Crucible)In a separate container, I mix my bone and wood charcoal together. I then fill the bottom 3rd of my crucible with this mixture.
I then start to add my parts I am going to case color harden. You must be mindful of the dump into the quench when you are placing parts into your crucible. You want the parts to hit the water edge or heavy end first. You must ensure that your parts do not hit the quench on the flat side or you will more than likely end up with warped parts, especially a part like a lock plate. I also like to place the parts in my crucible so the finished side is facing inward. Parts that are facing each other work like a shield to help keep the charcoal mix close to the parts. Here you can see the lock plate, cock, frizzen and a few of the screws in the crucible, all oriented so the parts enter the water edge or heavy end first. I make sure my parts are clean and dry but I do not degrease my parts or wear rubber gloves. The temperature you reach when case color hardening is hot enough to remove any fingerprints or oils that might be left from the skin. A lot of guys do degrease their parts and do not let their bare skin come in contact with the parts.
Another important step in the pack hardening process is to tap the sides of your crucible to get your charcoal to compact and settle. The denser you can get your charcoal, the better results you will obtain. I tap the sides of my crucible each time after I add a layer of charcoal and parts.
Before I place the tang in the charcoal, I make it a practice to cover the threads with a threaded collar. I want the collar to act as a heat sink and protect the threads from becoming overly hardened, eroded and/or brittle. It is just something I do.
Here you see the second layer of charcoal and parts added to the crucible. Again, take note on how the parts are positioned in the crucible. If you look you can see the tumbler bridle in the crucible. I harden the bridle because I feel hardened parts create less friction than non-hardened parts. Less friction means faster ignition.
Here is the crucible completely filled with my parts, charcoal and compacted as much as possible and leady for the lid to be installed and pinned in place.
Here is the crucible sitting in the oven ready to heat up. My normal process is to heat my oven up to a temperature of 1500 degrees f. It takes my oven about an hour to get up to temperature. Once it is up to temperature, I soak the parts for one hour before dumping the crucible into the quench tank. For years other people have been telling me that 1500 degrees f is too hot, but it works for me. For this session, I am going to do things a little different. I am going to program my controller to come up to 1400 degrees f , soak the parts for an hour and a half and then program my controller to drop the temperature to 1350 degrees f for 30 minutes. I have done this lower heat a few times and my parts always seem to come out with too much grey for my liking. The person who owns the lock I am color case hardening likes the greyer color pattern so we will see what happens. One advantage to quenching at this lower temperature is less warpage.
Color Case Hardening (Part 3, The Quench)Below is a picture of my quench tank. As you can see, it is nothing more than a 20 gallon galvanized trash can. The rectangular tube extending across the top of the trash can is used to set the crucible on when quenching the parts. There is a pin in the middle to hook the crucible lid to prior to quenching to keep the lid from entering the water and warping. I fill the tank with cold water from my well. You can see a small fish tank aerator that I use to help increase the dissolved oxygen level in my tank. I start the pump when I start my oven so I aerate for about 2 hours. Don’t know if this makes a difference or not. I have quenched with and without aerated water and cannot see any difference. The important thing to note is that you want the bottom of your crucible between 1 and 2 inches above the water level so your parts are shielded by the charcoal.
My friend Chris, the lock owner, is removing the parts basket from the quench tank. Having a basket is a lot easier than fishing out all the small screws and pieces with a magnet. One other helpful tip is to count the number of parts you are placing in the crucible. Then when you are retrieving the parts out of the quench tank you will know when you have them all.
Chris and I get our first look at how things turned out.
Color Case Hardening (Part 4, The Finishing Touches)Now it is time to temper. I temper at 425 degrees f for 1 hour, turn off the oven and then let the parts cool naturally in the oven.
After tempering, the toe area of the frizzen needs a little bit of special attention. I heat this area up chasing a blue color up to the pan cover. If you notice, I have the frizzen sitting on the heavy steel jaw of my vise. The steel works as a heat sink and keeps the face of the frizzen from losing its hardness. If you do not anneal this area, chances are good that it will snap off right in front of the pan cover. I also lightly run the face of the frizzen over the wheel of my 2’ x72” to remove the glass hard surface on the frizzen face. If this is not done, a lot of times the flint will just glide over the glass hard surface.
Before final assembly I like to chase the thread on all my screws and threaded holes. This cleans out any by-product from all the stress you have just put your pars through. I spray everything down with WD-40. You can use whatever light oil or rest preventative you would like.
