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Posted By: James M Case Coloring Question - 09/11/06 04:57 PM
I just finished cleaning one of my Colt SAA clones by Uberti which has a traditional blued and case colored finish. I noticed that the case coloring on this 15 year old gun is still pristine after thousand of holster draws and rounds thru it.
It is rare as we all know to ever find an original Colt or Parker with pristine case coloring unless it for the most part was an unused example.
My question is: Have they developed new and more durable forms of case coloring in the ensueing years?
Jim
Posted By: Rocketman Re: Case Coloring Question - 09/11/06 05:06 PM
Not really, but they have surely improved clear coat technology. I expect you are living proof that clear lacquor does a good job of protecting case color.
Posted By: Chukarman Re: Case Coloring Question - 09/11/06 10:32 PM
perhaps it would be useful to note that 'case coloring' and 'case hardening' are sometimes interchangeable terms. Many 'case colored' guns today seem to be just that - colored. Makers use various chemicals (like cyanide) to obtain a certain color. Early Perazzi guns come to mind.

Case hardening in traditional use was to apply a tough outer skin to metal using heat and carbon, quenched to set the hardness, which resulted in the distinctive coloration.

May be my imagination, but case COLORING does not seem to be as durable as case HARDENING colors. Perhaps soem of the smiths and rocket scientists could enlighten me on this.
Posted By: David Williamson Re: Case Coloring Question - 09/12/06 12:19 AM
Chukarman, Not a smith or a rocket scientist but I agree with you that case-hardening is tougher than case coloring. The colors from case- hardening are the result of the process. In order to case-harden you are using low carbon steel and you have to increase the carbon content of the surface of the steel so that a thin outer "case" can be hardened by heating the steel to the hardening temperature and then quenching it. So the process involves two seperate operations.
Cyanide, Carburizing, Carbo-Nitriding and Nitriding are all processes of case-hardening, but Cyanide is the most common. The steels are brought to about 1500 deg.F and then immersed in a bath of sodium cyanide. The hardening then is only a few thousands of a inch deep, .002-.004. and the depth is controlled by how long it is left at the 1500 deg.f before quenching.
I believe the case-coloring is of the Carburizing process where the parts are packed in a metal container with a carbonaceous compound (bone meal) surrounding the steel objects, the heat is higher 1700 deg.F for a length of time depending on the extent of the carburizing action desired. Now the steel can be hardened and quenched like regular high-carbon steel, now if they leave this step out you would get case-coloring. IMOP. Dave
Posted By: James M Re: Case Coloring Question - 09/12/06 12:31 AM
I went to the Uberti site and they use the term "case hardening" to describe the process used on their firearms. Now: Does anyone know what process either Colt or Parker originally used?
Jim
Posted By: tudorturtle Re: Case Coloring Question - 09/12/06 12:34 AM
JDW,
No offense meant, 'cause I don't know the difference; but I thought the cyanide process provided the same kind of surface hardening as the bone charcol process, but usually throws a different coloring style as C-man mentioned the P-gun type tiger striping (Philistine that I am, I like it).

And I do know that many steel parts are case hardened without coloring. Browning SP recievers were case hardened with no coloring.

There's folks here that really do know and we'll get the skinny soon enough.
Posted By: Ken Hurst Re: Case Coloring Question - 09/12/06 12:42 AM
Most color case hardening is done at 1400 ---1425 deg. The packing material is bone meal and wood charcoal. The more bone added the harder and the more charcoal added lowers the deg. of hardness. This also works with the colors --- brighter colors come from more bone, less bone gives less color. This is if the ratio of bone to charcoal is 60% bone to 40%charcoal.
Posted By: David Williamson Re: Case Coloring Question - 09/12/06 12:47 AM
Yeti, it does, but there are other steps to do in order to get there. I don't belive that gun companies selling guns at the prices that they did at the turn of the century would invest that much time in the process.
In order to get the parts not colored, just polish the csse off, and then blue them.
Posted By: 2-piper Re: Case Coloring Question - 09/12/06 02:28 AM
Critical temperature varies somewhat according to the carbon content of the Steel. According to "Machinery's Hadbook" low carbon steel is normally "Carburized" at temps of from 1650-1700°F while high carbon steel is sometimes "Pack Hardened" ie packed in a carbonaceous mat'l for protection of edges etc, in which case it should be heated only to about 1400-1450°F. As I recall the technique Oscar had worked out was to heat the part in the bone/charcoal mixture to somewhere around 1600-1650°F for carbon absorption then drop the temp down around the 1400°F temp which was still above the critical temp for the case which allowed it to harden upon quenching, but below critical temp for the low carbon core. This helped to reduce the warping tendency had the frame been quenched with the entire core above it's critical temp. Length of time at the higher temp in the mix controls the depth of case, but cyanide is normally not employed for other than a case of only a few thousandths of an inch thick. When greater depths are desired the charcoal mix is normally employed.
Miller
Note that much of this applies to industrial case hardening, wherecolor is of no concern. In fact machinery's Handbook does not mention "Color Case Hardening". The same general procedure applies though for the forming of the case & hardening it. The nature of the carbon determines the color I believe.
PPS Colt & Parker did use color case hardening as both used low carbon steel for their frames. They did "invest that much time in the process", but remember around the turn of the century "Labor" was cheap.
Posted By: Rocketman Re: Case Coloring Question - 09/12/06 11:59 AM
The hardening part of case hardening and the coloring are two separate steps. The carbon absorption occurs at higher temperature and the metal crystaline structure "set" by rapid cooling to below critical temperature (quenching).

The colors form on the metal surface from a thin, loosely bound layer of various "oxides and stuff." The "stuff" comes from the charcoal, bone, and quench water. Color formation is at lower temperatures and can be done independently of hardening.

Case hardening does not automatically produce a colored surface and a colored surface does not automatically indicate hardening.

The hardening is pretty much science. However, since people don't agree on the aesthetics of colors (brilliance, hues, etc.) and coloration patterns (stripes, pools, etc.), coloring is the domain of the artist.
Posted By: David Williamson Re: Case Coloring Question - 09/12/06 01:21 PM
2-piper, the information I wrote about was from the 18th Edition of the Machinist's Handbook. As far as how the "old masters" did it, most handed down until they found what they liked. It's a shame that most of it is gone or kept secret.

There is a good article in "Home Gunsmithing Digest" by Tommy L. Bish, published 1970, that goes into detail on how to case-harden, case-color parts.

As far as you saying they would invest that much time in the process because labor was cheap, I disagree, labor is still expensive, no matter then or now, $.20 /hr. then to $30.00 /hr. now, still relevant.
I know that L.C. Smith's parts were all hand fitted, and their case-hardening-coloring was some of the nicest around. So I cannot believe that that much time was invested in the process. I've never tried to file a case-hardened-colored piece to see if it was truly surfaced hardened. Maybe someone could tell us if they did. David
Posted By: Rocketman Re: Case Coloring Question - 09/12/06 03:18 PM
JDW = be assured that guns were case hardened for parts durability. Color was a byproduct. It is easy to forget that low carbon steel is pretty soft stuff. As far as gun design goes, case hardened low carbon steel is a pretty satisfactory material. While not as desirable as modern alloys, it still does a good job.
Posted By: Bill Hambidge Re: Case Coloring Question - 09/12/06 05:06 PM
Oscar Gaddy's DGJ articles/research seem pretty definitive to me. Extremely well done including photomicrographic work. His directions work well also-mixes with more bone charcoal(up to 50-50) favor the blue/green end of the light spectrum, lest bone(10%), favor the red/orange end. Best, Dr. BILL
Posted By: Ken Hurst Re: Case Coloring Question - 09/12/06 05:51 PM
I have tried cutting through new color cased pieces that were merely samples to find that most were hard enough that a momax steel chisel would break & skid off the steel surface. Needless to say, these same samples would resist being filed. FWIW, Ken
Posted By: 2-piper Re: Case Coloring Question - 09/12/06 07:17 PM
The process essentially as described in Machinery's Handbook, with the exception of adjustment of the carbonaceous mat'l for color, is what is described in W W Greeners book "The Gun" & is also given by an L C Smith engineer in the "Plans & Specifications" book. Many of the processes involved in producing these old classic guns from rust bluing, oil finishing stocks etc were all time consuming. For about the last 50 years I have read at every turn that the price of labor (Brought about by the labor unions, of which I was a member) was what killed the double gun in America. It was of course many more aspects involved, not the least of which was the desire for "FirePower". That time consuming method of case-hardening though was indeed the method by which the old classic gun-frames with color were finished. Chemical finishing of an alloy steel simply for the purpose of producing clor is a late phenomenum.
Miller
Posted By: Chuck H Re: Case Coloring Question - 09/12/06 07:44 PM
The one LC I tried to file was hard as a wedding....well suffice to say, it wouldn't cut with the file.
Posted By: Roy Hebbes Re: Case Coloring Question - 09/13/06 03:26 PM
Case colours are a very pleasing addition to any gun.The prime purpose of case hardening is to provide a hardened wear surface on the action, fore end, lock plates and certain pins and screws.The process is controlled so that the penetration of the hardening is limited to.005 inch approx; at the same time care is taken not to diminish the strength of the core metal.
Unfortunately in the process of recase hardening,increased case depth [carbon penetration]may result and the strength of the action of the gun may be significantly reduced.
Some years ago whilst reviewing restoration of a best English gun with a reputable English gunmaker, the issue of recase hardening was discussed.
The gun maker said they would not undertake the work unless I accepted full responsibility if the gun failed in reproof!
To illustrate their concern, he produced the action of a best London S.L.E. That had failed reproof following recase hardening.The failure occured at the junction of the water table and the vertical breech face, excessive carbon penetration was evident. My gun was hot recase hardened!
Recase hardening is currently in vogue. My question is: What process controls are currently used to avoid the problem described above?[ie:excessive carbon penetration and reduction in ultimate strength of the core metal]
Posted By: David Williamson Re: Case Coloring Question - 09/13/06 07:09 PM
Roy, Very good point. I think you hit the nail on the head. If the receiver, and if it has sideplates were originally case-hardened, had the case colors, and the colors wore off, the case-hardening would still be there. Now originally, the depth of the case-hardening was .002-.005. Re case-hardening the piece would definetly do something to the metal, what I don't know. Maybe there is a metallurgist out there that can add some light to the picture.
Posted By: 2-piper Re: Case Coloring Question - 09/13/06 08:35 PM
According to a letter from an engineer for L C Smith at Hunter Arms (written 1949) the procedure used there was to pack the parts in a crucible containing 3½ parts charcoal to 1 part charred bone. This was placed in a furnace, heated to 1600°F & held at heat for 2¼ hours. The crucible is then direct quenched into a tank of running, cold, soft water. I have in the past had access to a time/penertration chart for carburizing depths but do not have one here at home (retired). I would however expect this to give a minimum penertration of .010" to the case. Adding carbon to a low carbon steel of course does not reduce it's ultimate strength, but increases it. What can happen though is (as in the early 03 Springfields) the steel can be strong, yet brittle & unable to stand a "Shock". I am not up enough on this to say, if in "Re-Casing" penertration is accumulative, ie does it pick up where it left off, or does it have to start over. As this outer case is already carbon rich, I would assume it would immediately upon reaching temp begin to penertrate deeper, but this is simply a guess. I have always had great reservations about having a frame re-cased.
Incidently Cyaniding is normally limited to depth of less than .010".
Miller
Posted By: David Williamson Re: Case Coloring Question - 09/13/06 11:43 PM
2-piper, thanks for the information. In the article from "Home Gunsmithing Digest", that I mentioned earlier, it also stated about packing the parts in a crucible of steel and doing the same thing. It did not go into detail on re-doing case-hardening on the same part.
I have to go along with Roy and say I would be very skeptical about recase-hardening now that I have heard about his experience.
Posted By: James M Re: Case Coloring Question - 09/14/06 05:08 AM
It seems that this thread is wandering around a bit but a valid concern has been raised about re-case coloring(hardening) as a restoration process. It certain that this is routinely done by shotgun restorers such as DelGrego and Turnbull and I don't remember hearing about any negative results such as ruined frames until now.
Can someone elaborate on this?
Jim
Posted By: Oldmodel70 Re: Case Coloring Question - 09/14/06 05:49 AM
I would think the frames would be annealed first. Any polishing, filing, profiling, engraving, would be completed in the annealed state. Then the frames are re-casehardened. Would think most danger of brittleness from over hardening would be eliminated. Grant
Posted By: Rocketman Re: Case Coloring Question - 09/14/06 11:11 AM
The depth of carbon penetration is controled by time at heat. If it is believed that the current part is sufficiently hard, it is only necessary to recolor at coloring temperature (say in the 500 600 F range - and this is what several of the recolorers seem to be doing). However, to re-establish hardness, one needs to heat above critical for the given steel and quench. Time above critical has no effect on hardness other than increased cabron penetration (the iron "soaks" up more carbon to form a higher carbon alloy which may be harder). If it is believed that the carbon penetration on a given piece is sufficient, a heat to critical and immediate quench will keep carbon penetration to original, re-establish the OE level of surface hardness, and offer the option of re-establishing a color layer (case color) on the surface of the part.
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