From Wikipedia, the free encyclopedia

Bluing is a passivation process in which steel is partially protected against rust, and is named after the blue-black appearance of the resulting protective finish. True gun bluing is an electrochemical conversion coating resulting from an oxidizing chemical reaction with iron on the surface selectively forming magnetite (Fe₃O₄), the black oxide of iron, which occupies the same volume as normal iron. Black oxide provides minimal protection against corrosion, unless also treated with a water-displacing oil to reduce wetting and galvanic action.

In contrast, the red oxide of iron (Fe₂O₃), does not occupy the same volume as iron, thereby causing the typical reddish rusting away of iron. Both "cold" and "hot" oxidizing processes are called bluing, but only the "hot" process provides any significant rust and corrosion resistance, and then only when also treated with an oiled coating.

Contents [hide] 1 Usage 2 Hot vs. cold bluing 3 Limitations 4 Terminology 5 References 6 See also 7 External links

Usage

Bluing is most commonly used by gun manufacturers, gunsmiths and gun owners to provide limited resistance against rust while also improving the cosmetic appearance of the weapon, primarily by eliminating shiny reflections from the gun steel. Bluing, being a chemical conversion coating, is not as robust against wear and corrosion resistance as plated coatings, and is typically no thicker than 0.0001 inches (2.5 micrometers). For this reason, it is considered not to add any appreciable thickness to precisely-machined gun parts.

New guns are typically available in blued finish options offered as the least-expensive finish, and this finish is also the least effective at providing rust resistance, relative to other finishes such as Parkerizing or hard chrome plating.

Bluing is also used for providing rust resistance for steel parts of fine clocks and other fine metalwork.

Bluing is often a hobbyist endeavor, and there are many methods of bluing, and continuing debates about the relative efficacy of each method.

Historically, razor blades were often blued steel. A non-linear resistance property of the blued steel of razor blades, foreshadowing the same property that would later be discovered in semi-conductor diode junctions, along with the ready availability of blued steel razor blades, led to the use of razor blades as a detector in the crystal set AM radios which were often built by soldiers during World War II.

Hot vs. cold bluing

Bluing may be applied, for example, by immersing the steel parts of the gun to be blued in a solution of potassium nitrate, sodium nitrate, and water heated to the boiling point. Similarly, stainless steel parts of the gun to be blued are immersed in a mixture of nitrates and chromates, similarly heated. Either of these two methods is called hot bluing. There are many other methods of hot bluing. Hot bluing is among the most effective forms of bluing, providing the most permanent degree of rust-resistance and cosmetic protection of exposed gun metal.

There are also methods of cold bluing, which do not require heated solutions. Commercial products are widely sold in small bottles for cold bluing firearms, and these products are primarily used by individual gun owners for implementing small touch-ups to a gun's finish, to prevent a small scratch from becoming a major source of rust on a gun over time. At least one of the cold bluing solutions contains selenium dioxide, to accomplish the bluing. Cold bluing is not particularly resistant to holster wear, nor does it provide a large degree of rust resistance. It does, however, often provide a very good cosmetic touch-up of a gun's finish when applied and additionally oiled on a regular basis.

Cold bluing is often applied by first cleaning the steel area to be blued with alcohol, allowing the area to air-dry, touching a cotton swab in the cold bluing solution, applying one or more applications of the cold bluing compound to the steel being blued to match the rest of the hot blued finish, allowing the area to dry completely, and then using a good grade of gun oil to rub onto the cold blued areas, overlapping with the original hot blued areas. Provided regular oiling and rubbing is done, this method will provide adequate protection against rust for many gun owners.

Hot bluing and cold bluing kits and solutions are also sold commercially, for use by gun hobbyists.

Large-scale industrial bluing is also performed using a bluing furnace. This is an alternative method for creating the magnetite (black oxide) coating. In place of using a hot bath (although at a lower temperature) chemically-induced method, it is possible through controlling the temperature to heat steel precisely such as to cause the formation of black oxide (magnetite) selectively over the red oxide. It, too, must be additionally oiled to provide any significant rust resistance.

Limitations

Bluing only works on steel or stainless steel parts for protecting against corrosion. Aluminum and polymer parts are not blackened by applying bluing. Similarly, aluminum is not protected against corrosion by applying bluing. Other techniques must be used for protecting non-ferrous alloyed parts on guns against corrosion. For example, aluminum gun parts may be protected against corrosion using either patented processes (e.g., U.S. Patent 3039910 or U.S. Patent 2977260) or similar trade-secret processes.

Holster wear will remove hot bluing over long periods of use.

Terminology

Some prefer to call thin coatings of black oxide by the name gun bluing, and to call heavier coatings by the name black oxide, but they are both the same chemical conversion process for providing true gun bluing.

Historically, this process was also referred to as "browning" as many of the original finishes were brown rather than the safer-to-apply coatings that are blue and that became popular. (Many of the browning formulas, and the early bluing formulas, were based on cyanide-containing solutions, which are especially toxic.) The terms bluing and browning are interchangeable.

From Wikipedia, the free encyclopedia

Parkerizing (also called phosphating and phosphatizing) is a method of protecting a steel surface from corrosion and increasing its resistance to wear through the application of an electrochemical conversion coating. Parkerizing is usually considered to be an improved zinc or manganese phosphating process, and not to be an improved iron phosphating process, although some use the term Parkerizing as a generic term for applying phosphating (or phosphatizing) coatings that does include the iron phosphating process. Parkerizing is commonly used on firearms as a more effective alternative to bluing, which is another electrochemical conversion coating that was developed earlier. The Parkerizing process cannot be used on non-ferrous metals such as aluminum, brass, or copper. It similarly cannot be applied to steels containing a large amount of nickel, or on stainless steel. (See Passivation for protecting other metals.)

Contents [hide] 1 Application 2 Appearance and usage 3 Early history of Parkerizing (through 1942) 4 The future of Parkerizing 5 See also 6 External links 7 References

Application

The process involves submerging the metal part into a phosphoric acid solution whose key ingredient is often zinc or manganese, with varying additional amounts of nitrates and chlorates and copper. In one of the many processes that have been developed, the solution is heated to a temperature of 190-210 °F (88-99 °C) for a period ranging between 5 and 45 minutes. A stream of small bubbles is emitted from the metal part as the process takes place; when the bubbling stops, the process is complete. In addition to this particular processing temperature, there have also been various similar Parkerizing processes developed and patented that permit using either lower temperatures (for energy efficiency) or higher temperatures (for faster processing).

Appearance and usage

Zinc phosphating results in a non-reflective, light- to medium-gray finish. Manganese phosphating produces a medium- to dark-gray or black finish. Iron phosphating produces a black or dark gray finish similar to manganese phosphating. The grain size of the zinc phosphating is usually the smallest among the three processes, providing a more appealing cosmetic appearance in many applications. Many firearms that are Parkerized turn to a light greenish-gray color within a few years, as the coating ages, with the protective coating remaining intact. Cosmoline, especially, interacting with Parkerizing, can cause the highly-desired and attractive greenish-gray patina to develop on firearms that are stored in armories.

Manganese and iron phosphating coatings are usually the thickest electrochemical conversion coatings, being thicker than electrochemical conversion coatings such as zinc phosphating and bluing.

All of the electrochemical conversion coating finishes are not painted coatings, but chemically become part and parcel of the metal surface to which they are applied.

As for all electrochemical conversion coatings, the Parkerized surface must be completely covered with a light coating of oil to maximize corrosion and wear resistance, primarily through reducing wetting action and galvanic action. A heavy oil coating is unnecessary and undesirable for achieving a positive grip on Parkerized metal parts.

Alternatively, the Parkerized surface may be painted over with an epoxy or molybdenum finish for added wear resistance and self-lubricating properties.

Early history of Parkerizing (through 1942)

Development of the process was started in England and continued by the infamous Parker family in the United States. The terms Parkerizing, Parkerize, and Parkerized are all technically registered US trademarks of Henkel Surface Technologies, formerly Parker-Amchem, formerly Parker, formerly Parker Rust-Proof Company, formerly Parker Rust-Proof Phosphating Company of America, although the terminology has largely passed into generic usage for many years. The process was first used on a large scale in the manufacture of firearms for the United States military during World War II.

The earliest work on phosphating processes was developed by British inventors William Alexander Ross, British patent 3119, in 1869, and by Thomas Watts Coslett, British patent 8667, in 1906. Coslett, of Birmingham, England, subsequently filed a patent based on this same process in America in 1907, which was granted U.S. Patent 870937 in 1907. It essentially provided an iron phosphating process, using phosphoric acid.

An improved patent application for manganese phosphating based in large part on this early British iron phosphating process was filed in the US in 1912, and issued in 1913 to Frank Rupert Granville Richards as U.S. Patent 1069903.

Clark W. Parker acquired the rights to Coslett's and Richards' US patents, and experimented in the family kitchen with these and other rust-resisting formulations. The ultimate result was that Clark W. Parker, along with his son Wyman C. Parker, working together, set up the Parker Rust-Proof Phosphating Company of America in 1915.

Colquhoun of the Parker Rust-Proof Phosphating Company of America then filed another improved phosphating patent application in 1919. This patent was issued in 1919 as U.S. Patent 1311319, for an improved manganese phosphating (Parkerizing) technique.

Similarly, Baker and Dingman of the Parker Rust-Proof Company filed an improved manganese phosphating (Parkerizing) process patent in 1928 that reduced the processing time to 1/3 of the original time that had been required through heating the solution to a temperature in the precisely-controlled range of 500°F to 550°F. This patent was issued as U.S. Patent 1761186 in 1930.

Manganese phosphating (Parkerizing), even with these process improvements, still required the use of expensive and difficult-to-obtain manganese compounds. Subsequently, an alternative technique was developed by the Parker Company to utilize easier-to-obtain compounds at less-expense through using zinc phosphating (Parkerizing) in place of manganese phosphating (Parkerizing). The patent for this zinc phosphating (Parkerizing) process (utilizing strategic compounds that would remain available in America during a war) was granted to inventor Romig of the Parker Company in 1938 as U.S. Patent 2132883, just prior to the loss of easy access to manganese compounds that occurred during World War II.

Somewhat analogous to the improved manganese phosphating process improvements discovered by Baker and Dingman, a similarly-improved method was found for an improved zinc phosphating process as well. This improvement was discovered by Darsey of the Parker Rust Proof Company, who filed a patent in February 1941, which was granted in August 1942, U.S. Patent 2293716, that improved upon the zinc phosphatizing (Parkerizing) process further. He discovered that adding copper reduced the alkalinity requirement over what had been required, and that also adding a chlorate to the nitrates that were already used would additionally permit running the process at a much lower temperature in the range of 115°F to 130°F, reducing the cost of running the process further. With these process improvements, the end result was that a low-temperature (energy-efficient) zinc phosphating (Parkerizing) process, using strategic materials which the United States had ready access to, became the most common phosphating process used during World War II to protect American war materials such as firearms and planes from rust and corrosion.

As a tragic aside, during the Great Depression, Parker Company co-founders Clark W. Parker and his son Wyman were found guilty of investor fraud. The details of the story were contained in a 20 July 1931 Time Magazine article: "Clark W. Parker and his son Wyman stood before Federal Judge John Munro Woolsey in Manhattan last week, were fined $11,000 each and sentenced to five years in Atlanta Penitentiary for conspiracy and using the mails to defraud. Worthless was not only $1,250,000 worth of stock in Automotive Royalties Corp. but also that of two previous companies Mr. Parker had formed. Many a mulcted clergyman sadly agreed when Judge Woolsey called him "an enemy to society." Swindler Parker shrugged." "[1]

The future of Parkerizing

Traditional iron phosphate, zinc phosphate, and manganese phosphate electrochemical conversion coatings, including Parkerizing variations, have all been criticized in recent years for introducing phosphates into ground water systems, encouraging the rapid growth of algae. As a result, in recent years, new, emerging technology alternatives to traditional phosphate coatings have started to see limited use, for replacing all phosphating coatings, including Parkerizing. The majority of these newer conversion coatings are fluorozirconium-based. The most popular of these fluorozirconium-based conversion coatings, introduced in 2005, incorporates the transitional metal vanadium. This new, more environmentally-friendly coating is referred to as a vanadate conversion coating. Besides vanadate coatings, arsenate coatings may theoretically provide similar protection, at the risk of being a health hazard to humans and animals. It remains to be seen if these, or other new electrochemical conversion coatings, will ultimately replace traditional phosphating and Parkerizing.