Bluing Methods, Definitions and Processes by Bill Adair The following is a comprehensive discussion of all the bluing (and related) methods employed in my restoration business, and probably includes every bluing method known to man. The types of bluing are listed alphabetically with a notation of the type; i.e., 'Salt', 'Heat', etc. This is intended only to describe the various kinds of bluing and to clarify the mass confusion regarding certain terms such as 'Carbonia' and 'DuLite'. Another purpose is to describe what modern small-shops do to duplicate the methods that might have been used by Colt and others well over a hundred years ago; i.e., where the results are identical, but the methodology is not. In general, this is not a how-to. Do-IT-Yourself preparation and bluing generally results in disaster. A good portion of the work I get is fixing other peoples attempts at polishing, bluing, or whatever. Leave it to the pro's! Proper preparation (polishing) takes many years of experience, and the setup costs for equipment and supplies for just one type of bluing can run to $1,000 or more easily. The perpetual argument of when or why a gun is restored, in my opinion, is a stupid and completely un-necessary one. There's basically only one rule, and it's simple: If a gun has already been seriously 'messed with', then it's no longer original, and it's ok to fix (restore) it. If it has been mangled by overbuffing, bad preparation, incorrect bluing, or had any of a myriad of other no-no's done to it, then there should not be any argument against restoring it. If it's a good, original gun with honest wear and tear or normal age-related ills, but is generally in the 'collectible' range, then leave it alone. A gun that is pitted or otherwise abused is generally not a 'collectible', even if it's original. Just because someone might buy it doesn't make it collectible. I'd guess that over 90% of my restoration work is done on abused, messed-up guns that are not collectibles in any sense of the word. CARBONIA Heat/Chemical Now here's one of the most mis-used, least-understood words in the entire bluing lexicon. 'Carbonia' Blue was a S&W proprietary method used in the period from before WWI thru the 1960's. It was also known as 'Smith & Wesson blue'. It was ONLY done by Smith. Never by Colt or any other manufacturer. Carbonia bluing resulted in that deep-black/glossy high-polish finish that Smith was noted for during the years they used it. It's similar to 'DuLite' and Charcoal bluing as far as the process goes, but certainly not the same. The Carbonia oil (a product of American Gas Furnace Co.) was used by many gun manufacturers in their own versions of 'DuLite' bluing, but the use of Carbonia oil does not make it 'Carbonia Blue' as only S&W did it. DuLite bluing, such as Colt did on their 1918/1919 military model 1911's is an industrial/utility finish. It was generally done over a fairly coarse-polished and/or sandblasted surface, and is a dullish, dark-grey or near-black color when used in that way. It was also far less durable than the S&W Carbonia Blue. And there's a funny story to go with the S&W Carbonia Blue. I'm telling it like I heard it, and I have no idea if it's true. The basis of S&W Carbonia Blue was an oil mixture (pine-tar based) made by the American Gas Furnace Company, and they supplied the oil in bulk to S&W, who mixed it with bone charcoal and other 'stuff' to make their own Carbonia product. Years ago, by the way, I contacted the American Gas company for info on the process, and they were kind enough to give me a list of the chemicals/ingredients used by Smith for the process, but it was just a list of chemicals, not a formula. So, here's the story: Apparently, only one old-timer at Smith knew the exact formula and he had it in a notebook which he kept. He eventually retired from Smith, and later died. His widow, so the story goes, contacted Smith and offered to sell them the formula in the notebook for $50k. I guess she knew that her husband had the only written copy of the secret formula. Well, Smith had gone into hot-bluing by then, and wasn't really interested in shelling out $50k to her for the Carbonia formula. So, she burned the notebook. And that was the end of Carbonia. The moral of the story is that all of these companies who now say they do 'Carbonia' bluing, or worse yet 'Colt Carbonia blue', are just you-know-what. Maybe they can do something that looks similar to S&W Carbonia Blue, but it ain't. And Carbonia blue is not Charcoal blue. It's very black the way Smith did it, not blue, and please, Colt never did it. Carbonia, when applied to a surface that is not expertly high-polished, results in just a so-so utility kind of blue. Time and temperature controls were critical in obtaining the exact color Smith desired. I've still got the list of ingredients, but there are numerous items on the list, and you'd need to combine them in the correct measures to get the actual S&W formula. I've combined most of the ingredients (or similar ones) in various percentages and at one time did quite a bit of R&D with it, but I never got too interested in pursuing it much further. It was hard enough to find any whale, let alone a sperm whale, so I never had any sperm-whale oil. That was just one ingredient I couldn't locate. American Gas Furnace Company doesn't make the stuff they supplied to Smith any more, so it's a futile pursuit as well as further proof that true Carbonia bluing no longer exists. However, the Carbonia look can be simulated or duplicated by other means. ________________________________________________________________________ CHARCOAL Heat/Chemical Charcoal bluing is done at about 730-750 degrees F., with organic charcoal (not wood charcoal). Organic means any leather, bone, bone meal that has been charcoalized and crushed into very small chips. I use commercially-prepared bone charcoal only. This is the most time-consuming (read 'expensive') form of bluing. Very labor-intensive, and you have to know the correct chants to say while doing it. For one-gun, small-shop applications, a large motor-driven drum is rigged up which drops hot charcoal particles and dust on the parts as the drum rotates, and as the parts rotate inside the drum. Every half-hour or so, the parts are removed and wiped down with an oil-soaked, lime-covered rag, which removes any built-up oxidation. It often takes 8 or so cycles of heat/wipe-down to get the full, consistent color. It has often taken me an elapsed time of 12 hours to do one gun, with maybe 3 hours of that actually involved in the wipedown process. If you can do that without burning your hands off, then you're a professional. Charcoal produces a blue that is less 'transparent' than Nitre-bluing, but about the same medium-blue color. The process of steel-making was considerably improved during WWI, with higher carbon content and certain alloys added. These steels resist straight heat-bluing (Nitre or furnace), and the charcoal method was developed to deal with the newer steels. Later, around WWII, steelmaking was again improved with more alloys, and frames and slides were also heat-treated to a higher Rockwell. These WWII and later steels resist both Charcoal and Nitre heat-bluings. Thus, charcoal bluing is a 1920's-1930's method only. One thing that just thrills us is to discover a gun with modern look-alike small parts on it. Sometimes the only clue comes after the rest of the gun is blued, and those aftermarket ones are still red. Worse, the aftermarket parts are cast look-alikes. Cast parts can look exactly like originals, but they sure don't take the bluing. ________________________________________________________________________ DULITE Heat/Oil/Chemical This is one of my favorites because everyone on the planet has his own idea of what Dulite bluing was (Circa WWI years) and is now (Hot-Salt method), and they're all wrong about the early years. Given the mass confusion r.e. 'DuLite', we'll spend some extra time on this one. First, bear in mind that the 'Hot Salt' method was invented by Mauser, circa 1937, and first used on Mauser Lugers beginning around mid-1937. Obviously, a Colt 1911 made in 1918/1919, and finished with what is now referred to as the 'Black Army' finish, was not done with Hot Salt bluing, since it was not invented until 20 years later. The origin of the word 'DuLite' eludes me, but in some vintage literature, the term 'DuLite machine' comes up, along with 'Dulite machine operator'. These (sic) 'machines' were gas-fired ovens into which parts were placed after being steam-cleaned, and the parts were covered with a variety of 'chemicals' and substances. These would include charcoalized bone chips, pine-tar oil and/or whale oil. The parts were rotated via a lever-driven gizmo once in a while as the oven heat (prox 550-700+ degrees F.) baked the parts in the bone/oil concoction. Sometimes the heated parts were rubbed down with rags soaked in the plant's oil waste, and sometimes just blown with an air hose. Note from this basic description that this process describes a subset of Heat-Treating, or more specifically, the 'drawing-back' (tempering) of hardened or heat-treated steel to a less-brittle state. It also describes a basic 'Charcoal-bluing' method. It also describes a basic 'Oil-quench' bluing method. So, what was 'DuLite': a part of a heat-treating/tempering process, a charcoal-bluing method, or an oil-quench bluing method? How about all three! Taking a step back, if you polish (i.e., sand or buff) a steel rod to some grit level, and then heat the end with a torch to about 700 degrees, then plunge it into a cup of motor oil, it's going to turn the heated end black, with the less-heated part of the rod further up showing a blue or purple color. Repeat this several times and the blackened end will get even blacker. This is an oil-quench bluing (actually 'blackening') method, producing an industrial-looking black finish which is quite crude looking. Many manufacturers use the same oil-quench method today to blacken tools and all sorts of parts, like screws, to put a rust-inhibiting finish on them. The blackening will be glossy or dull depending on the level of the polish. In the old days,almost every military-firearms maker used this 'DuLite' blackening method for many parts, and this method is still used for the same purpose. The 'DuLite' process, then, was a combined method for tempering and industrial-blackening of steel. Today, the DuLite Company just sells their own brand of salts used for Hot-Salt bluing. The modern Dulite Company and their products have absolutely nothing in common with the vintage process called 'Dulite' bluing, any more than the 'New' Springfield Armory had anything to do with WWI Springfield 1911's. It could be that the predesessor to the modern Dulite Company supplied the furnaces of that name, or the modern name may simply have been 'borrowed', like 'Springfield Armory'. I've tried to contact the modern Dulite Company several times for historical info, but they've never responded to my emails. My own 'Dulite' process for finishing 'Black Army' Colt's is similar to the vintage method, but is scaled down to one-gun-at-a-time type of work. The last thing I need is a humongous gas furnace and smokestack sticking up over my shop. _________________________________________________________________________ HOT-SALT BLUING Chemical: Caustic Alkaline with low heat Most Hot-Salt bluing is done with salts purchased from a supplier. My favorite is a product called 'Black Magic'. It gives a super dark-blue (not black as the name implies), and is a trouble-free product. Hot-Salt bluing is done in a tank at a relatively low temp of prox 280 degrees F., is virtually idiot-proof, and takes little time. After the solution is at the working temp, then 10-15 minutes of bluing time is all you need. Hot Salts are very caustic. They'll even rot wood, so this is an outside-only method. A few people have indoors rooms that are highly ventilated, but I recommend the great outdoors for this. Hot-Salt bluing is appropriate only for 'modern' guns (WWII to present). _________________________________________________________________________ NITRE BLUING Heat; various temperatures Also see Straw and Fire-blue below Nitre is the short-name for Potassium Nitrate, usually mixed with Sodium Nitrate. These chemicals are salts that are normally purchased pre-mixed from a supplier, like Brownell's. Nitre-bluing is a very old method well-suited to old-time, low-carbon steels. It is basically a one-gun-at-a-time substitute for gas-furnace bluing, such as used on pre-WWI Colts, and is a superior method, in my opinion, for low-volume applications. The salts melt starting at around 375 degrees as the cast-iron container is heated to prox 730-750 degrees. Yes, 730-750. Ignore the Brownell's instructions regarding temperature. I once wrote them a 7-page letter advising them how Nitre-bluing is done, but it was ignored. They still insist on 570-600, which will get you nowhere. At the 730-750 temp., the parts are immersed (small parts in stainless mesh baskets, large parts on black-iron wire) in the melted salts. About 12-15 minutes is plenty of time. The parts are extracted, hung on the wires to cool, then rinsed with warm water and oiled. Both gas furnaces and nitre rely on heat alone to get the color desired. I believe the nitre is superior to the furnace method because it's liquid, and there's absolutely no oxygen in it to cause oxidation as might happen in a large gas or charcoal furnace. And the temperature can be precisely controlled. Other than methodology, there is absolutely no difference between nitre and furnace bluing. The results are identical because both rely only on proper heat to obtain the bluing. A super-polished model 1911 made in early 1912 will have the frame and slide the magnificent royal-blue color, and the small parts fire-blued. Both are done nowdays using the Nitre method, just at different temperatures (see Fire-bluing below). Again, the modern term 'Nitre' bluing means a result that is exactly the same as the early Colt (and others) gas or charcoal furnace bluing. _________________________________________________________________________ OIL-QUENCH Heat/Oil This is a method that is almost never used for bluing whole guns, but it's a great way to 'touch-up' parts instead of using cold-blue. There is no such thing as a 'good' cold-blue. Period. End of that story. Cold-blue is bad stuff. To see if a part has been cold-blued, just put some alcohol on a paper towell and wipe it across the surface. Any cold-blue that was on the gun will partially come off and will leave the paper towell blackened. The oil method can be applied two ways: Heat the part and drop it in a cup of motor oil, or heat the part and swab motor oil on it with a cotton ball held with pliers. It's going to smoke like crazy, so this is best done outside. Best to heat the part to about 700 degrees. It will usually take several applications to get the desired color. Temperature can be guesstimmated by taking a piece of polished junk steel of about the same thickness as the part to be blued, and counting how many seconds it takes for the torch to temper-color the piece to a darkish blue. It will take about twice as long to get dark blue as it does to heat it to a straw color. This is a method that takes some practice to perfect, especially where you're trying to touch up a small area in the middle of an existing blued part, such as a spot in the middle of a blued slide. Don't try it on a real part till you can get good results on a test piece. _________________________________________________________________________ RUST BLUING Chemical/Process The process of rust-bluing involves applying the rust-blue chemical, then allowing the part to surface-rust. After a good coat of brownish rust is built up, the part is boiled for about 10 minutes. The boiling turns the brown rust to a black oxide. When cool, the black oxide is 'carded' off with steel wool or a carding wheel, leaving the surface blackened. Usually 3-4 cycles is needed. My recommendation for rust-blue formula is Pilkington's American Rust-Blue, from Brownell's. _________________________________________________________________________ STRAW Heat Both Straw and Fire-blue are not technically 'bluing'. They're temper colors that polished steel takes on as a result of heating to a specific temperature. Straw is done at about 450 degres, and fire-blue at about 550 degrees. Both are done the same as Nitre-bluing, as far as using Potassium Nitrate and Sodium Nitrate heated to the correct temperature is concerned, but the parts (submerged in a steel basket in the heated solution) are removed when they're 'done', like baking cookies. Too much or too little time in the heat will result in a too-light' or 'too-dark' color, even if the temp remains constant, so the parts have to be watched like a hawk. Modern-steel parts take longer than old-time, low-carbon steel to produce the correct color. If you want to see the range of temper colors, polish a steel rod and hold a torch to just one end. Heat the end slowly and the more-heated end will turn light-blue or fire-bluish, while the less-heated portion above will turn straw, with various shades of purple in-between. Fire-blue is also called 'Peacock' blue, which is a close description of the color. __________________________________________________________________________ FIRE-BLUE Heat See 'Straw' above. _________________________________________________________________________ _________________________________________________________________________ COMBINATIONAL METHODS Over the years, I've developed bluing methods that combine 2 of the above methods by doing one type right over another type. These methods were basically developed to achieve a certain look to the bluing, such as '1900 Luger Blue'. I haven't named the methods, and only refer to them by the purpose for which they're intended, such as the specific look of 1900-1906 Lugers. By combining methods, I've added about 4-5 ways to get certain vintage bluing looks that are not otherwise obtainable due to the unavailability of vintage chemicals, such as 'Spirit of Nitre', aka Nitrous Ether (highly expolsive), or lack of a supplier for something I need (such as a specific rust-blue formula). A couple of these methods will also blue cast iron or cast steel parts in the same look as Nitre blue. _ _________________________________________________________________________ Important Considerations Regarding Early Steels and Finishes: Almost everybody, I’d bet, thinks that the early Colt, Winchester, Remington, etc., products were flawless, and that they left the factories with perfect finishes. That is just not the case. It’s very true that the craftsmanship back in the old days was truly amazing and the work was superb, especially given the crude machinery and tools they had to work with. However, the steels used were poor, and the finishing methods were far less than ideal. This combination led to finishing flaws that were very common, and here’s why: Steelmaking improved considerably during WWI, and probably even more during WWII. Prior to WWI, the quality of steel was poor. Domestic steel was not very homogeneous, meaning that the ‘ingredients’ were not very evenly distributed in the molten state. Batches of steel also had varying amounts of impurities such as sand, silicon and who-knows-what. German steel of the time was far superior and, for a time, Colt imported German steel. Steel used by the factories came from various steelmakers, and the quality varied considerably. This early steel was low-carbon, low-alloy mild steel. Finishes of the time, specifically furnace bluing and charcoal bluing, are also less than ideal. They can produce some beautiful results, but both are ‘temper’ blues, rather than blues that bond to the steel, such as a modern hot-salt blue. Temper blues simply change the color of the steel according to the temperature used. They do not change the chemical makeup of the surface of the steel. Temper blues are very finicky and the results of temper bluing are very dependent on the nature and quality of the steel. If a piece of early steel has ‘clumps’ of impurities, the hardness of that ‘clump’ is going to be different than the area between one clump and another. These clumps can be of various sizes from a few molecules to fairly large areas. Depending on the chemical makeup of a given clump, it is likely to temper-blue differently than an area directly next to it. During heat-treating, these clumps can harden differently, as well. They can be softer or harder than other, more homogeneous portions of the same piece of steel. If a clump is much harder, red or plum spots may develop. If softer, darker blue spots can show. Generally, these clumps are very small, and so the differences in the bluing from one small area to another are imperceptible. However, larger clumps are subject to showing badly. Factories tended to blue parts in batches. For example, a batch of slide-stops might be blued many months from a batch of thumb-safties (to give a 1911 example). These 2 batches would probably be done in different ovens, using slightly different temperatures, and different amounts of time, and by different people. In the end, these 2 parts wind up on the same gun. Are they exactly the same color? Probably not. Close, but not exact. Early steel is also subject to striations (discussed elsewhere). Guns were shipped to military and civilian markets with striations showing. They were not scrapped or re-done. Bluing flaws such as spots, mottling, etc., also did not prevent the gun from being shipped, assuming the flaws were within an acceptable range for military or commercial consumption. New guns were probably over 99% ‘good’ blue, with no perceptible flaws, but almost every gun would have some flaw(s), somewhere on it. When you think of how a gun made it from New Haven to New Mexico, having been packed into wooden crates and shipped by stagecoach or rail, over the worst terrain, and maybe attacked by Injuns, the shipping and handling damage to a ‘new’ gun was probably much more severe than mere bluing flaws. You just didn’t worry about that stuff back in the frontier days. You were just glad it got there at all. Now, when an old gun is restored properly, using the early bluing methods, the same problems arise: bad steel + temper bluing = unpredictable results. Customers should expect no level of perfection greater than what the factories were able to produce. And, the earlier the gun, the more likely it is that steel and/or bluing flaws will appear on the newly restored gun.