Color Case Hardening

Left: Robin Brown removes a packed pot from the kiln and heads for the cold-water quench. Right: an action body freshly imbued with color and a hardened surface.
Left: Robin Brown removes a packed pot from the kiln and heads for the cold-water quench. Right: an action body freshly imbued with color and a hardened surface. Photographs by Matthew Brown
By Douglas Tate

Finishing is a defining element of fine British gunmaking: a dash of scroll on the locks, the deep luster of an oil-rubbed stock and the rich blacking of the barrels. But perhaps even more significant is the color case hardening, which is the icing on the cake and serves to both protect and provide a splash of color where none otherwise would exist.

According to Daryl Greatrex, until recently the managing director of Holland & Holland: “In our view the traditional method of color case hardening used by Richard St Ledger [in Birmingham] produces the best results, giving a brilliance and depth to the colors that cannot be achieved using other methods.” These days few British gunmakers color harden their own guns, but David McKay Brown, in Scotland, and Robin Brown of A.A. Brown & Sons, in England, do. According to McKay Brown: “In the early days of gun manufacturing—the 18th Century—wrought iron was used for the frames and lockplates of the muzzleloaders. It was soft and easy to machine, to work using hand tools and also for polishing and engraving. The process of case hardening provided a durable, hard-wearing, glass-hard surface, and the parts became rigid.”

Writing in The Modern Shotgun, Volume I: The Gun, Maj. Sir Gerald Burrard suggested that in the old days the engraving was there to provide decoration to the metal when the case hardening wore and that the real beauty was the color hardening. I put this to Robin Brown. “Never heard of the engraving being there to show up once the color has gone,” Brown said. “New one on me! Some guns had minimal engraving, and the color was the decoration, true. Border-engraved guns for instance.”

Jonathan Irby, James Purdey & Sons’ gunroom manager, offered this: “The color finish was—and is—the by-product of the hardening process. This is favored as providing a hard surface with a certain level of flex underneath, rather than a glass-hard finish.” Hardening incorporates carbon into the molecular structure of the surface steel and occurs when hot steel is splashed into cold water. The process gives the outer steel an armored skin that prevents wear and corrosion while preserving the interior, ductile, shock-absorbing strength. Other finishes such as silver, nickel and coin are available, but these, too, are first typically hardened in the traditional way.

Like alchemists, gunmakers can be secretive about their dark arts, but Robin Brown and David McKay Brown were both helpful in explaining how the colors are achieved. “Cleanliness is paramount,” Robin Brown said. “The work must be totally grease free when it is packed in the bone charcoal, which must also be as grease free as possible. If there is a small amount of grease or oil in the medium, closely mottled hardening is likely to be the result, with strong possibilities of flaking. Flaking is when the top finish of the hardening color flakes off, leaving a pale gray showing underneath. It is hard to hide and usually leads to a re-harden.”

Bone charcoal is a mixture of finely and coarsely smashed and ground animal bones. In the past other adjuncts were not unusual, according to McKay Brown. “It was common to use not only wood or bone charcoal but other materials such as clippings from horses’ hooves and scraps of leather,” he said. These days in some workshops bits of hardware—washers, bolts and even specially shaped blocks of steel—are wired to the backs of less-dense components such as triggerplates, locks and straps, to distribute color more evenly.

Once the components to be colored are clinically clean, the procedure known as “the packing of the pots” begins. Care is taken to make sure that large components like the action body are centered in the bone charcoal and that no two pieces touch. Next the pot goes into a preheated kiln. “One of the best-known men for color case hardening in the Birmingham quarter was Bill Woodward,” McKay Brown said. “Bill would judge the length of time it took for his box to come up to temperature by the time it took him to drink a couple of pints in the pub! Good results can only be achieved by a great amount of trial and error.

“Starting from the time I was an apprentice, I have always experimented with color case hardening; and although over the years I have hardened a number of boxlocks, some of the results have been disappointing. Once a triggerplate broke in two due to brittleness. So when it came to hardening my first round-action gun, which had taken four years to build, I was very nervous. I made the charcoal from gardeners’ bone-meal fertilizer by toasting it in a heavy frying pan. The smell could be detected 500 yards away! Malcolm Appleby had engraved the gun and asked if I could produce a good blue. One of my men was recording the procedure. I quenched the action body, and on taking it from the water I exclaimed, ‘Well, if Malcolm wants blue, he has got f***ing blue!’ What a relief!”

Temperature and timing are crucial: the higher the temperature, the shorter the bake, and vice versa. It’s essential that all metal parts are left unpacked—contained in their envelope of bone meal as it is deftly tipped into the quench. Exposure to the atmosphere can cause unwanted dull-gray colors. Or, as Robin Brown puts it: “If an area is gray, it is usually because the steel item came in contact with air [oxygen] during the tip. We would say it had ‘flashed.’ Looks awful, and a bad flash would have to be re-hardened to overcome it. We do all we can to avoid a flash.”

According to Burrard in The Modern Shotgun, Volume I: “After the case-hardening the gun is reassembled and can be considered finished. The side plates and the action are sometimes given a coat of thin varnish to protect them and preserve the colour. But this varnish soon wears off, seldom lasting more than a season. For this reason I have made it a practice with one gun of mine which has an exceptionally beautiful colouring to have the side plates revarnished at the end of each season. The result has certainly been gratifying and the colour is as good as ever, although other guns made at the same time have lost theirs.”

The colors themselves are perishable from sunlight and wear. The remaining colors on vintage guns offer a “rule of thumb” indication of cosmetic condition. Rubbing, wear and wiping can result in fading. This fading is varied and occurs first along edges. Some prefer brilliant cobalt, others the fade of old blue jeans, gold or khaki. The ideal, at least for me, is a comfortable used appearance—worn Levis with an old work shirt.

David McKay Brown offers this: “We case color every gun. The work is done in house and with more control. In my opinion the beauty of a gun is in its graceful and elegant lines, with the engraving tastefully cut, not distracting from the overall design. The colors of case hardening are a dressing that wears off with use, bringing the engraving to life.” Bright and bold or old and used, color case hardening is a defining element of best British gunmaking. 

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  • Extremely informative article by Tate. I agree that nothing adds greater “distinction” to a fine field gun than color case hardening. My experience is limited to the work done here in the states by Doug Turnbull in Bloomfield, Pa., but that one experience convinced me that if I was ever to have another gun case colored, he would do the work. Covid-19 shut them down in April, but Turnbull Restorations is now back up and running. I have the 1911, Ithaca Flues 20 gauge double restored by Turnbull near two decades back displayed on my web site, although It probably is not permissible for me to link my blog on this page. I think Doug may also have my photos of his work on Grandfather’s Flues linked on his “shoot-history/Turnbull Restorations” page.
    Keep the great articles coming, Shooting Sportsman !

  • Thought turnbull was a new yorker?????? I live near Bloomfiel and don’t recall a turnbull in area.

  • Thanks, Bill and John. Age keeps catching up with me in the form of inaccurate key strokes. I toured Turnbull Restorations in Bloomfield, NY two decades ago when I visited Ithaca Classic Doubles in Victor.

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