We have had several inquiries lately regarding our finishing practices; mainly as to whether or not firearms are parkerized before they are cerakoted, and if cerakote is applied to the interior of the gun. The short answer is “No” and “Yes.” However, these are not arbitrary decisions; they are supported by analysis and support that is often lacking in the firearms industry. For those interested in the science behind these decisions, please read on.
Parkerization, or phosphating, is a well known process for protecting ferrous metals from corrosion, as well as increasing wear resistance. It is specific metal treatment that falls under the generic term ” metal pickling.” Metal pickling is a centuries old process developed primarily to remove impurities, rust and scale by immersing it in a strong acid. It is technically a trademarked term, coined by Clark Parker, who purchased the rights to the original process from two British inventors, and later developed the different techniques described below.
Parkerization goes one step further then Pickling by altering the surface material, changing it from regular iron to Iron Phosphate.
2 Fe(s) + Fe3+(aq) + 3 H2PO4–(aq) → 3 FePO4(s) + 3 H2 (g)
Parkerization Chemical Reaction
Additionally, Either Zinc or Manganese can be added to the acid solution; both of which yield slightly different material properties and appearance. Pure Iron phosphating result in a black to dark gray, non-reflective finish. Manganese phosphating is a slightly lighter gray, and Zinc phosphating produces an even lighter gray.
Zinc and Manganese Parkerization
With age, it can develop a slightly green hue as the finish ages, especially if coated with Cosmoline. This however does not affect the performance of the coating. The parkerization process has evolved throughout the years; with the two main foci being increased corrosion resistance, and the speed and temperature at which the process takes place.
On a Chemical level, Parkerization is a great improvement over untreated metal, but it is not a perfect solution. Due to the chemical behavior of the phosphate compound, the Iron can still react with oxygen in the air, in a process called Galvanic Corrosion. For this reason, Parkerized materials should still be lightly coated with oil in order to prevent corrosion. It is not a “coating” in the traditional term, but a chemical process, like the oxidation process that aluminum undergoes that allows for its immense corrosion resistance.
Moving forward several decades, the original Guns built by Germany were parkerized, with an additional paint layer over the top. This functioned as a barrier, reducing the likelihood of corrosion, and removing the need to maintain an oil coat. This represents the best solution available at the time, by combining two mediocre performing finishes. There is no additional reason behind combining these, no mystic ability developed by Heckler and Koch that somehow trumps modern alternatives.
Moving forward to modern times, coating technology improvements have produced some truly space-age products; Tenifer, Diamond-Like coatings (DLC), and our chosen product, Cerakote. Cerakote is a cured finish, that bonds directly to the host material, it provides fantastic corrosion and scratch resistance with the introduction of a ceramic compound, similar to what is used in Brake Pads. In addition to its corrosion, wear and scratch resistance, the “smoothness” of the ceramic compound results in a lower coefficient of friction, allowing mating surfaces to grind less when in motion. IT IS A STAND ALONE PRODUCT. We have spoke with NIC industries, the company that owns Cerakote, as well as several other Licensed Cerakote appliers, including the applicator for Silencerco and Redcreek tactical, and they have all stated clearly that “Cerakote performs best when applied directly to untreated ferrous metals.”
The reason behind that becomes clearer upon further analysis; Cerakote is unique in its formula composition with the addition of ceramic compounds, and is specifically formulated to achieve the best bond possible with the host material. In order to do so, it must be able to “react” with the iron, in order to complete the chemical bond necessary for adherence. Parkerization is well known to assist in adherence of common paints and coating, because the addition of the phosphate molecule (an organic compound) serves as an anchoring point for bonding of most coatings, which also primarily consist of organic compounds. Parkerization therefore reduces the possibility of bonding with Cerakote, because the phosphate compound blocks the inorganic Ceramic material from bonding with the inorganic Metal compounds. Those of you familiar with chemistry or metallurgy might state that the ceramic compound should be able to easily bond with the carbon atoms in the steel, but the Carbon content in the receivers is exceptionally low, less than 0.1%.
The Cerakote will still adhere, as it will to almost any material (including polymers,) but instead of being a finish bonded to the host material, it merely “floats” over the top, with no chemical reaction taking place. PARKERIZATION PRIOR TO CERAKOTING RESULTS IN AN INFERIOR PRODUCT. To be fair, cerakote is a coating, unlike Parkerization, so the degree of bonding that takes place is far less. However, the comparably small amount of bonding that takes place is vital to achieve the maximum performance with the product.
A Horrible Cerakote Application
Another argument against parkerizing first arises from the metallurgical process of parkerization. The term Metal Pickling is a colloquialism for a common materials process called conversion coating. In summation, the acid dissolves the top layer of the metal crystalline structure, which combines with the byproduct from that reaction (the phosphate molecule) in the acid solution and forms into a hard, brittle precipitate.
This results in a hard, durable outer layer to resist wear, with a softer interior to absorb impact. By Cerakoting a parkerized component, two hard layers (the parkerized surface and the ceramic coating) are in direct contact, then subjected to repeated impacts every time a round is fired. Imagine taking two coffee mugs and beating them against each other repeatedly. One, if not both of them will crack and eventually shatter. Now take a coffee mug and beat it against the sole of your shoe. Just like when you place newspaper in between your dinner plates when you have to put them in a box, it becomes fairly obvious why you need a softer material underneath the Cerakote; it allows the coating to resist wear without succumbing to impact damage.
As if this wasn’t enough of a reason not to parkerize, yet another argument against it exists; it is an unnecessary expense. Parkerization, except for on a molecular level, does not increase the thickness of the material. Cerakote is a coating, and therefore does result in a measurable thickness increase. It is also several times more scratch resistant than parkerized metal. If an event occurs that is able to remove the cerakote finish, it will undoubtedly penetrate through the microscopically thin parkerized layer reach the host material. There is no conceivable scenario where Parkerization will prevent damage that cerakote will not. Continuing the analysis from a cost perspective, Cerakote was chosen over some of the other more modern or exotic finishes available for several reasons, one of which is price. A tenifer or DLC coated gun in theory would be more durable, but would easily double the cost for finishing. Cerakote’s ease of application results in a more time efficient, repeatable, uniform finish, which will come into play later in this discussion.
The last portion of this discussion relates to the second question, do we cerakote the interior of our guns. The thought process behind not coating the inside of the gun is due to the properties of the cerakote itself, it does in fact add to the thickness of a material, which can affect tolerances.
Over-applied Cerakote Application
(resulted in failure to cycle)
However, if properly applied by a licensed applicator, the resulting dimensional changes are less then .002″, which is well within the dimensional tolerance for our guns. Again these tolerances are based off the original specifications from Germany, with coherent analysis and adaptation taking into account our differing methods and materials. This is another topic entirely, which is covered in depth in our article on “HK spec.”
Some might say even the remote possibility is too much of a risk, but the benefits provide even further credence. The first benefit is of course due to the material properties of Cerakote; reduced wear and friction results in a longer lasting, smoother running gun. The other benefit is less obvious, but equally crucial. By not coating the inside of the gun, a clear boundary is created between portions of the firearm that have been coated, and portions that have not. This discontinuity, like those seen on the end of a piece of wood, result in minute imperfections and sharp spots that, on a microscopic level, are easily chipped off when they come in contact with other materials. This creates a “splintered” finish in these areas, allowing the cerakote to be chipped off, exposing the material underneath. This actually would be the only instance in which parkerization would be beneficial, as it is the only way the cerakote could be removed without a scratching or penetrating action.
For those of you still reading, We commend you for your drive to understand what some believe to be a trivial subject. It is that same drive and attention to detail we use on all of our products, and is why they perform as well as they do. Even if you do not purchase a firearm from us, we hope it is helpful in your other pursuits. The bottom line is that when choosing to have a gun finished with Cerakote, make sure it is from an applicator Licensed by Cerakote. It is easy to confirm this through their website, and the only way their guarantees and warranties will apply. There is no shortage of grifters, confidence men, and slackers wanting to take short cuts in this business, we want to make sure that your money does not perpetuate their practices, even if its not used to buy one of ours.
On a final thought, we do believe that improvements can always be made in any product or process, and we will never expect anyone to take our conclusions as gospel. If a more convincing argument exists that contradicts our thoughts, we welcome comments and input. We do however request that this argument be supported with objective analysis, and not opinion or anecdotal evidence. Please feel free to respond with your thoughts.