How to Blue A Gun Like a Gunsmith
What Does It Mean to Blue a Gun?
Bluing a gun is to finish it with a bluish colored tint that improves anti-rust properties, scratch resistance, and makes for beautiful eye candy. When it comes to firearms, a deep, sleek, and captivating blue finish is unlike any other finish. It’s also easy on the eyes, sporting excellent glare reduction. Bluing means to treat the steel by removing the free iron from the metal’s surface. Normally an acid solution is used for this process, which is called passivation.1 Most gunsmiths use the modern technique of hot bluing to accomplish the blued finish. One of the cool parts about blued firearms would be the wide range of shades achieved from applying varying layers of finish. However, before a gunsmith attempts to blue a firearm, there are some important things to consider.
Note: Many people spell “Bluing” with an E:“Blueing”. Although the correct spelling is Bluing, both methods are interchangeably accepted in the firearm community. Yes, we are talking about the same thing.
Things to Consider Before Bluing A Firearm
True bluing techniques take much more than simply dipping a gun into a solution. Although, there are most certainly a number of shady services that will cheaply blue a firearm with a number of quick techniques. Real gunsmiths accumulate a lot of experience and equipment which help them provide a professional refinishing for a blued firearm. Many materials and guns respond differently to various bluing techniques, therefore, suggesting ample experience and research is necessary to be able to properly blue every gun. Additionally, aluminum and polymer gun parts cannot be blued at all.
If there is any rust present, it must be removed and the gun restored as best as possible before it can be blued. This means fully disassembling the firearm, scrubbing free the red oxide rust, and thoroughly cleaning the gun. If the gun was already blued and it is being refinished, the old blued finish must be removed before the new finish can be applied. Assuming there is a gun which can be properly blued, a walkthrough for bluing a gun is rather easy to follow!
What is Carding (in Firearms)
Whether one is a professional gunsmith or a hobbyist, carding is an important part of bluing a firearm. Because it is such a critical step in the process, it is important to understand how it is performed before going into any bluing process. In the simplest of terms, carding means to clean new rust away from gun parts as it is created in the bluing process. Typically gunsmiths will use degreased, fine steel wool. Albeit, some gunsmiths will argue that steel wool is a bit abrasive, and have opted for hand brushes or wire wheels. It does pay off to care about creating scratches on the firearm in this process. Even if using a wire wheel or other head with an automated system, making contact with the parts gently goes a long way. Carding is essential to be able to layer additional coats onto the gun in the bluing process, and for applying any oil at the end.
The Process of Bluing A Gun: Preparing the Firearm
Properly bluing a firearm is an art and a professional skill. A blued gun commands respect and so does a skilled gunsmith with the technique to create the blue! Skip no steps to achieve a blued finish that stands out like none other.*
*Even the Deoxidizing and Rinsing steps will be important to providing a chemically clean gun to get the most out of the bluing process.
Determine the Eligibility of the Firearm For Bluing
Although it was already previously mentioned, aluminum and polymer parts cannot be blued. If the firearm is rusted, the rust needs to be removed before it can be blued. If the gun was previously blued, the old blued finish needs to be removed before the new one can be applied.
Disassembly and Deoxidizing
All traces of old finish need to be removed using a process called deoxidizing. A 50/50 solution of water and hydrochloric acid fills a crockery tank or glassware with a depth that will support the thickest of the gun parts to be blued. The part is immersed into the acid. It is important to keep the fumes within the container, and thus a tight fitting cover must be used at all times. This cover should be made of lead or rubber-lined wood. The fumes are so important to keep contained because of their effect on other metal parts within the shop. These fumes can literally coat surrounding guns, tools and equipment, with a layer of rust. It is further ideal that the bluing process be kept contained within a room or enclosure of its own.
The process may need to be repeated, as the parts should not be left in these baths for more than a few moments at a time, and rinsing must ensue after each immersion. The immersion time for each part is going to varies, as each part cleans at different rates.
Safety Disclaimer: Working with acid can be dangerous, and thus the gunsmith needs to wear rubber apron and elbow-length rubber gloves, as well as a face mask and goggles. The acid can burn the skin and lungs. Never inhale the fumes of hydrochloric acid, as it is of poor odor and will induce coughing, sneezing, or vomiting. Setting up a fan or blower motor can help improve the ventilation of the room or enclosure used for bluing.
Assuming there has been an old finish being removed, the next step is to rinse the parts in a tank made of black sheet iron, filled with water and a few ounces of alkaline cleaner. Lye can also be used. This bath actually neutralizes the effects of the acid, and dissolves anything remaining on the surface of the gun parts. Each part that is rinsed requires an new solution for the next. In some circumstances, a gunsmith is rinsing many parts to the point actual running water is preferred. The rinse tank should be kept away from the rest of the shop and other metal parts.
Tip: Using a tank that also has a drain of some sort makes changing out the solution much easier.
Denickeling (optional phase, where applicable)
Removing nickel finishing in order to blue a gun requires a special process called Denickeling (or stripping the nickel). If the parts are made of iron or steel, the nickel plating can be stripped and the gun can still be blued. The stripping method is the easiest way to strip nickel from a plated gun. The gun is disassembled, and provided the gunsmith does not have access to the equipment and resources themselves, the parts are sent to a plating company which can remove the plating in a stripping bath.
If a gunsmith prefers to denickel themselves, a special bath must be made for part immersion. The solution for removing nickel and copper plating from steel and iron is a simple formula: 10.5 ounces of ammonium persulate, 5.25 ounces of ammonium carbonate, and 3 quarts of liquid ammonia (28 percent). A glass Pyrex pan works very well for this job, just as long as it is deep enough to accommodate the largest of gun parts. This is because even the slightest bit of nickel remaining can destroy an entire blue finishing. Sometimes nitric acid is used as an alternative solution for denickeling.
Remember, a gun must first be cleaned before it can be denickeled. And always use bore plugs, no matter how they need to be made. Rubber plugs are adequate for this step. Wooden plugs should be avoided, as they are highly absorbent and will not fully block the solution from permeating the plug.
Stripping Copper (optional phase, where applicable)
The formula for stripping copper from steel can be made from mixing: 10.5 ounces of sulphuric acid, 6 pounds of chromic acid, and 1.5 gallons of water. This cold solution will remove a thick coating of copper within roughly 30 minutes. If the solution is heated, it can accomplish the stripping within 5 to 10 minutes. Always remember to pour the acid into the water, to avoid splatter.
Grinding and Polishing Phase (The Pre-Bluing Phase)
Since the deoxidizing and rinsing steps provide fully chemically clean parts, they are ready to be further prepared for bluing. Regardless of the type of bluing technique that is employed, the blued finish will only be as impressive as the material surface it is applied to. Possessing the right equipment for resurfacing a gun part to a flawless polish can be invaluable to a gunsmith. The goal is to obtain a blemish-free surface before the bluing process begins. It is critical that all scratches and dings are as resurfaced as possible to avoid the blue finish from appearing in greater concentrations throughout these imperfections.
The polishing head is typically about three quarters an inch in shaft diameter, and threaded for 2 1/2” at each end. Heavy iron or steel sporting tapered roller bearings hold the shaft. The motor should be half a horsepower or greater with a step cone pulley. Preferably, a two place step cone pulley is ideal, allowing for the variation of 1:1 and 2:1 shaft speeds. The general rotation range should be between 1,500 and 3,750 RPMs. This setup can be used for all types of gun work. Typically the shaft is also well-secured via bolts into a reliable and sturdy stand or bench. Ideally, the pedals are controlled by the foot, leaving the gunsmith’s hands open for the demanding process of grinding and polishing. The most important polishing wheels to keep in stock include canvas wheels, walrus leather wheels, and cloth buff pads. The canvas wheels should be 6 or 8 inches in diameter and between 2 and half an inch wide. The walrus leather wheels should be the same size range as the canvas wheels. The cloth buff pads should be 10 inches in diameter and between 2 and 3/8 inches wide.
Depending upon how much finish or surface needs to be addressed in the grinding and polishing phase, abrasives may come in handy. Certain abrasives, such as emery or aluminum oxide, can be used to dress the wheels to make polishing more efficient. Sometimes wire wheels will be required to remove certain types of paint. Some polishing wheels will appear as though they are not making an immediate impact on the metal surface. The amateur gunsmith may overlook actual layers of metal being removed from the part.
Constructing a Bluing Tank (when necessary)
A bluing tank is recommended for a gunsmith to be able to blue guns on a regular basis. Bluing tanks are best made of black iron (or sheet iron). Other acceptable materials include: wood tanks, lead-lined tanks, stoneware tanks, glass pans, stainless steel tanks, and iron tanks. The bluing tank must be able to support submerging the largest sized gun part. Any metal baskets that are used to hold small parts should be of a fine mesh. The mesh baskets cannot be galvanized or it will contaminate the bluing solution. This contamination can create unsightly grease and rust streaks.
Selecting a Bluing Technique
Although there are many bluing techniques, they all produce different quality finishes. The type of bluing technique a gunsmith will choose varies upon the preferences of the gunsmith, equipment available, and many other variables.
Important Note: Always remember to properly plug all barrels before immersion in bluing tanks. And do not use wood plugs, as they absorb solutions and fail to do their job. Rubber plugs and certain metal plugs are best.
Bluing Technique #1: Cold Rusting Process
This is often considered an outdated technique and is not very commonly used in any recent year. Regardless, it can still produce high quality work if done correctly or another method is not possible. There are some records of this process being used as far back as the early 1700s. Cold rusting does make it extremely easy for a gunsmith to determine when the desired shade of blue has been achieved, and to cease the process. Cold rusting is well-known for producing extremely rich, satin blues.
The process means thoroughly coating cleaned parts in a bluing solution and then hanging them to dry. The solution variables may differ from gunsmith to gunsmith; and therefore, it is important to understand the rusting time will be different for each solution. After the rusting period is complete, the part is carded. The part can be boiled (in water), re-dried, and then re-coated in the bluing solution to repeat the process. The process can be repeated as many times as necessary until the desired color is reached. Deeper tones of blue will require many more cycles than lighter tints. Many steels require up to five or more cycles to achieve deep satin finishes. Before an additional cycle can begin, or before the final product can be oiled, the parts need to be carded after each rusting period.
These are the best formulae for Cold Rusting:
Bluing Solution Option #1:200 grams of Iron Chloride, 200 grams of Antimony Chloride, 500 ccms of water, and 100 grams of Gallic Acid.
Bluing Solution Option #2:50 grams of Mercuric Chloride, 50 grams of Ammonium Chloride, and 1000 ccms of water.
Bluing Solution Option #3:600 ccs of Nitric Acid, 400 ccs of Hydrochloric Acid, add iron horse shoe nails until the acid stops creating fumes, mix into 5 litres of water, and let sit for 3 days. [this method is for experienced gunsmiths only]
Important: All water needs to be distilled. And solutions should be mixed carefully in wide-mouth jars, grinding these kinds of substances can be dangerous.
Bluing Technique #2: Hot Rusting Process
Hot Rusting is often called the “quick method” for rusting and was the forerunner strategy for many gunsmiths for a very long time. It has only been replaced in recent years by the hot dip process, which will also be detailed below. Practically speaking, the hot rusting process is still useful for some guns and parts which cannot be completely disassembled and safely immersed in a hot dip bath. The process is very similar to the cold rusting process, less for the immersion of the parts in boiling water. This is done to speed up rusting, which is then dried by heat. Just like the cold rusting process, parts undergoing the hot rusting process still need to be carded.
The best setup is a 2 or 3 tank process which moves the parts through a cleaning phase, a rinse phase, and then a boiling phase. The parts typically spend about 4-5 minutes in the cleaning tank, a few moments in the rinse tank, and then another 3-5 minutes in the boiling tank. After being removed from the boiling tank, a pre-heated bluing solution is “painted” onto the parts using a swab or similar transfer cloth. The color difference will be immediately noticeable as the solution is applied to the parts. If the color is not of a blue, gray, silver or blackened tone, there may be an issue and the solution needs adjustment. In many cases, the solution needs to be further diluted using distilled water. The parts will dry rapidly, and can even be sped up with a light fan. As soon as they are dried, they must be reimmersed into the third tank, where they are boiled for a couple more minutes.
After pulling the parts back out of the boiling tank and allowing them to dry (happens quickly), the newly formed rust should be immediately carded off. Once all rust has been removed, the remaining color reflects the newly added layer of blue. The first layer is most important to inspect carefully, as any spots or areas which were missed can be more carefully attended to in future coats. The parts can be reboiled in the third tank, with new solutions applied, and carded, as many times as necessary to achieve the desired depth of blue. The heat of the boil is typically between 270 and 315 degress Fahrenheit.
These are the best formulae for Hot Rusting:
Bluing Solution Option #1:220 grains of Sodium Nitrate, 220 grains of Potassium Nitrate, 400 grains of Bichloride of Mercury, 400 grains of Potassium Chlorate, 18 ounces of water, 2 ounces of Spirits of Niter, 2/3 ounce of Nitric Acid, and 2/3 ounce of Ferric Chloride (29% – tincture).
Bluing Solution Option #2:220 grains Potassium Nitrate, 220 grains Sodium Nitrate, 460 grains Bichloride of Mecury, 400 grains of Potassium Chlorate, 20 ounces of water, 2/3 ounces of Spirits of Niter, and 1 ounce of grain alcohol.
Bluing Solution Option #3:1 ounce Copper Sulphate, 2 pounds of Iron Chloride, 8 ounces of Hydrochloric Acid, 1 ounce of Nitric Acid, and 2 gallons of water.
Important: All water needs to be distilled. And solutions should be mixed carefully in wide-mouth jars, grinding these kinds of substances can be dangerous.
Bluing Technique #3: Phosphatizing Process
Phosphatizing is typically not used in a gunsmithing shop, or in any hobbyist activities. This process was created for military finishes and is only used in industrial settings. This does not even include all gun manufacturers. Phosphatizing requires expensive and complicated equipment, which is why it is usually only used in a large, industrialized manufacturing operation. Some of the common names for the finishing processes which utilize phosphatizing include: Bonderizing, Coslettising, Fermanganising, and Parkerizing. Phosphatized finishes are typically rougher than most finishes and a poor choice as a coating for some moving parts. Still, this process picked up in popularity around the World War II, with even some of the most inappropriate parts being coated.
Bluing Technique #4: Bone and Oil Process
Bone and Oil bluing produces amazing finishes and is used by some of the most respected brands. This process still requires rigorous cleaning, grinding and polishing. Bone dusting and oiling create a layer on the gun before it is prepared for the heat. The gun parts are then mounted on specially created racks which are inserted into a furnace. The heat needs to be controlled and there cannot be any moisture or humidity present. This type of bluing produces an impressive coat. There are many mixtures which exist to produce a premium bone and oil bluing, however, they vary greatly depending upon the type of metal that is being blued.
Copper and Brass respond well to Potassium Sulfide and Ammonium Hydrosulphide mixtures. Brass also has a nice reaction to Iron Nitrate and Sodium Hyposulphite mixtures, as well as to Copper Carbonate and Ammonium Hydrozide mixtures. Aluminum will turn black with the right Potassium Permanganate, Nitric Acid, and Copper Nitrate mixture. Cadmium can be turned black using a Copper sulphate and Potassium Chlorate mixture. Iron and Steel can be colored with a Lye and Potassium Nitrate mixture. It is imperative to create the right bath temperature depending upon the solution being used, as all of these solutions become effective at different temperatures.
Note: This method is generally only used in industrial settings and is not recommended for a hobbyist, amateur, or small gunsmith shop.
Bluing Technique #5: Flame Bluing Process
This method is considered a very manual process and is typically only used for a small pin or similar sized part. It is also very seldom used. Still, when a single pin or screw needs to be blued, it is silly to setup an entire bluing bath. Instead, a light concoction of linseed oil and motor oil (50/50) can be blended and used to attain the desired color. Basically, the part can be held over a flame until it turns dark red, and then dipped into the solution. This will generate a blue shade on the part, which can be darkened with repeated heating-immersion cycles. Remember, it is still important to thoroughly clean and polish any parts prior to introducing them to the oil solution. As rare this technique may be in use, it is most certainly used at least once in a while by nearly any serious gunsmith hobbyist or practicing, professional gunsmith.
Bluing Technique #6: Hot Dip Process
Hot dip bluing is one of the newer techniques of bluing which has only been around since the early 2000s. This method became so popular because it gave gunsmiths the ability to blue up to 20 or more pistols at the same time. And they can be finished in less time than it takes to hot rust a single gun. This process does require a larger tank in order to service more than one gun, however, no bore plugging is necessary for this method. Because all of the parts are blued at once for each gun, they are also very consistent in color. This method also requires the least amount of skill. As long as the temperature is monitored and maintained, the job will produce a beautifully uniform blue. Still, the parts need to be polished after the bath is done and they have cooled.
Warning: Failure to keep the hot dip bath within the recommended heat range can create adverse affects on the metal in form of hard-to-remove deep red rust.
Unfortunately, not all guns can be hot dipped for a blued finish. Double barreled shotguns, for example, have soldered parts which are negatively affected. Any guns with soldered parts or similar joints, will do poorly in a hot dip. The process literally affects the integrity of soldering to the point the gun may malfunction. So as a general rule: never hot dip any soldered parts.
There are three well-respected hot dipping techniques known as: Ebonol, Jetal, and Pentrate. All three processes produce great blued finishes, and none of them appear to be significantly better than any other. Making the bath itself means mixing water with various bluing salts, being sure to keep note of the correct operating temperature for said bluing salts. All of the bluing salts and hot dipping techniques typically work within the hot dip boiling point of about 265 to around 345 degrees Fahrenheit. It is acceptable to add water to the hot dip tank throughout the process in order to keep the working temperature in the correct range.
Never use any copper in the hot dip process, as it is extremely problematic for the developing parts in the bath. Rust streaks will be evident and very hard to get rid of in the event copper makes its way into the process (even if just to hang the guns). In fact, the “no copper” rule should expand to include all non-ferrous metals.
Tips For Bluing A Firearm
The bluing techniques are always improving, and new techniques for bluing are invented all the time. Trade journals and sites like Armory Bay provide the latest information for the development of things like bluing. Many gunsmiths develop preferences to particular ways of doing things, and bluing is a fine example. One gunsmith may prefer a certain technique and believe it produces the highest quality blued finish, while another has much better results with an entirely different method of doing things. Never forget that an already blued gun must first be stripped of all old blue finish before it can be reblued. Nickel plating also must be fully removed before a gun can be blued.
It is imperative to possess good equipment for properly prepping a gun for bluing. It is necessary to follow proper cleaning techniques. Blued guns can be many different shades and qualities, depending upon the time spent, experience of the gunsmith, and quality of the equipment.
For more information about the durability of a blued gun, check out our other article: The Durability of Blued Finish.
Disclaimer: A lot of these skills require precision expertise and should only be attempted by a professional gunsmith with proper equipment and facilities.
1The Rust Store. (2019). What is Stainless Steel Passivation. The Rust Store. Retrieved from: https://www.theruststore.com/What-is-stainless-steel-passivation-W85.aspx
About the Author:
Mark Doberman, The Proprietary Gun Smith
The Proprietary Gun Smith is a marksman, expert gun handler, ammunition specialist, survival guru, and lifetime gun enthusiast. He owns (or has owned) nearly every legal firearm and ballistic available, has fired nearly every gun, and regularly consults professionally in the firearm world. He has studied firearms and similar tactical lifestyle for more than 40 years. In addition to writing for ArmoryBay.com, TheProprietaryGunSmith has guest written for more than a dozen other sites and/or magazines in the industry.
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