After the blade of a knife is completely forged and heat treated, it needs to get some final touches to give the surface its final looks and character. This process, known as blade finishing, is important not only for the looks of a knife, but for the service properties as well. Explore various options of blade finishing in this brief guide.
A blade is finished to achieve a certain grit of the finished surface. A low-shine finish has 280 to 320 grit, while a mirror-shine polish has a very high grit number providing a perfect sheen. The average standard for high-quality knives is about an 800 grit finish. A higher polish shine can be achieved with buffing using chrome oxide (white chrome, green chrome) or by hand polishing with a very fine abrasive paper. Japanese water-stone allows achieving a grit as high as 10,000 to 12,000.
A hand satin finish is worked by sanding the blade through gradually increasing grades of abrasive grit. A good satin finish showcases the shapes of the blade and reduced reflective glare. This type of finish is usually applied to upscale custom knives that require a hand-made sleek look valued by collectors. With an increase in grit number, finer abrasives will produce smoother lines and a cleaner finish. Satin finishes are also used on the handle or fittings of a knife to improve overall appearance. A thorough hand satin finish performed by a seasoned master can increase the price of a knife.
A mirror polish provides a bright, glary sheen to the knife blade. This type of finish requires a sandpaper somewhere from 2,000 to 4,000 grit. The resulting shiny finish has a number of advantages: first of all, it is aesthetic. Then, a mirror-polished knife is much better at push-cutting operations, such as shaving, chopping, or carving. Merely sharpening a blade does not provide good edge retention: a well-polished blade is needed, and a high-grit polish will reduce the risk of dulling. Remember, that mirror polish is easily scuffed, so this type of finish is more likely to be used on high-end, showpiece knives. Applying a mirror finish takes a lot of skill, and retaining this upscale polish requires careful maintenance.
Stonewashing distresses the blade using friction to create a whacked look. During the process, a knife blade is run through the dryer with small stones or other abrasive material to create grazes on the blade surfaces. The technique speeds up the normal aging process, removes sheen and hides scratches and defects. The knife may look differently after the stonewashing procedure, depending on the type of abrasive used, the tumbling technique and the method of prior finishing. Stonewashing is an affordable option that may produce a curious finish with primitive household equipment. Remember, however, that stonewashing dulls the knife blade, so you’ll need to resharpen it afterwards.
Bead blasting is an affordable, less aggressive surface finish option. It is a flexible surface finish process that involves shooting glass, ceramic or steel beads at high pressure to give a uniform finish of the material. The versatile process works with various materials from stainless steel to brass and even plastic, and is suitable for a wide range of purposes. Different results, in respect of visual effect and roughness, may be achieved depending on the size and shape of the blasting beads, the speed and the pressure during the procedure. Typically, a semi-polished, satin finish with a soft, matte look is achieved. A higher of lower grade of reflectivity and a darker or a lighter color can be achieved, depending on the media. The surface can be made more or less dull, satin, or rugged. Bead blasting is known to result in a smooth and even finish. It also improves the mechanical strength and aesthetics of the surface. With proper settings, the bead blast finish can even harden a material and increase its durability.
Knives meant for heavy-duty use may require a coated finish. These typically come in darker colors, provide great rust resistance and reduce wear and tear. You should be cautious with coated finishes as they can be scratched off easily. In such a case, they should be recoated to restore their appealing appearance.
A quality coating on the blade can considerably increase the working lifespan of the knife. Some coatings (for example, DLC – Diamond-Like Carbon) are expensive, but they will be worth the splurge if you consider the added value of corrosion prevention and easier maintenance of your knife.
Gun blue is popular today, as it was long ago. This old method of steel coating derives its name from the blue-black color imparted to gun barrels after a treatment. Dense layers of black iron oxide (magnetite) left after the process provide protection of the surfaces and the bluish black color of the “gun blue”. Perhaps the oldest and most popular technique, bluing is still widely used as it is very easy, relatively safe and cost-effective. The cheapness of the bluing method saves a deal of maintenance efforts and expenses. However, bear in mind that bluing products are intended for minor touch-ups only, and the procedure shouldn’t be applied to a whole blade. A blade is not perfectly corrosion resisting after bluing, and you should be prepared to blue your blade on an ongoing basis.
Anodizing (or anodization) is an electrolytic process that converts the surface of a metal (for example – titanium) into a durable protective coating of metal oxide. The process is accomplished by immersing the metal into an electrolyte bath. An electric current passing through the medium releases oxygen ions to combine with metal atoms and form metal oxide at the surface. The oxide structure originates from the metal substrate and is fully integrated with the underlying metal, so it cannot chip off or scale.
Anodic coatings are highly resistant and timeproof, they remain stable and unfading even in areas subject to rough operation and abrasive abuse. Anodized surfaces are known to resist corrosion better than non-treated metal. The lifetime of the anodic finish depends on the thickness of the anodic coating applied.
Teflon is a type of plastic sprayed on various surfaces and then baked to create a non-stick, waterproof, and nonreactive chemical coating. It is used to prevent buildup from various adhesive materials during use. However, remember that Teflon coating is not good for kitchen knives. The only FDA-approved coating cures at a high temperature that can affect heat treatment of an industrial knife. Therefore, knives to be used in the kitchen should not be coated with Teflon.
Titanium nitride (TiN) coating is a hard ceramic powder that is wear resistant and chemically inert. It is used on various tools and surfaces, increasing tool lifespan two to ten times. TiN coatings have a broad range of applications due to great practical properties such as high hardness, corrosion resistance, reduced friction, and wear resistance. TiN coatings are used on various metals, for hardening cutting and sliding surfaces. TiN is often used for providing inert coatings for surgical devices. When applied to knives, this coating reduces friction on the blade surface and hardens the cutting edge against wear.
The titanium carbo-nitride coating (TiCN) is a coating type that offers a high hardness combined with a good toughness, resulting in additional tool life. Carbon in a TiCN coating increases hardness nearly 80 percent over a TiN film. TiCN has the highest lubricity of all the TiN coatings, providing great hardness and wear resistance. It is known to achieve superior abrasive wear resistance. Being an excellent all-purpose coating – TiCN is commonly used for cutting or forming harder materials, due to its higher surface hardness.
Hard chrome, also known as industrial hard chrome, functional chrome, and engineering chrome, is an electroplated surface finish technique. During the hard chrome electroplating process, chromium is deposited onto a surface from a chromic acid solution. Combined with a base metal substrate, hard chrome finish achieves high quality and efficiency of the product. It is known for its wear and corrosion resistance and, especially, low friction characteristics. Hard chrome plating is widely used due to its effectiveness. Industrial hard chrome finish increases the working lifespan of a knife as it protects the blade from oxidation and improves surface hardness.
BlackWash is a specific knife blade finish, a combination of black coating and stonewash finish. Black coating uses a chemical bath to transform the upper layer of the steel to magnetite. It improves corrosion resistance and adds an aesthetic look. After coating the blade black, the stonewash finish is added. The whole process produces a vintage, worn look like that of a used tool. Also, the resulting surface structure hides use scratches and adds knife protection. This variation of the stonewash finish has become quite popular over recent years.
DLC (Diamond-like Carbon Coating) covers the blade with a thin film of carbon atoms with hardness similar to that of a natural diamond. DLC is the hardest coating used on knife blades. Along with superior hardness of the blade, it features very high abrasion resistance, low friction and excellent corrosion resistance. The pitch black color of the DLC coating also provides anti-reflection properties for knives. Surfaces coated with DLC withstand wear from chemical agents, dampness and other atmospheric conditions. They are immensely durable and have a longer operation life.
In this process, a fine powder is applied with an electrostatic spray gun that causes powder particles to adhere to the steel, and then cured under heat. The dried powder is known to produce a smooth, even, durable and very tough coating. The process is now applied to a variety of products, including knives.
PVD (Physical Vapor Deposition) coating is also known as Thin-Film Coating. During the process, a thin film of a solid material – metal and/or ceramic – is vaporized in a vacuum environment and deposited, by condensation, onto the blade surface. The coating, deposited atom by atom, forms an extremely pure multi-layer, bonded structure that greatly enhances the look and function of the blade. PVD deposites films at the atomic level, thus allowing to finely control the structure and density of the coatings. PVD is widely used at the industrial scale and is capable of producing coatings with excellent service properties. PVD coatings are known to provide high durability, hardness, lubricity, great corrosion resistance and scratch resistance. PVD coatings greatly reduce friction and block damage from atmospheric factors.
Cerakote is a polymer-ceramic composite coating made out of resin and hardener. The unique formula provides an excellently hard finish and makes Cerakote a high-performing coating that improves a number of functional properties such as abrasion resistance, corrosion immunity, and impact strength. Cerakote is baked onto the working surface, that is, cerakoted blades are subjected to high heat when applying the coating. The process is known to provide superior protection against such factors as chemical attack, heat and ultra-violet, making it a perfect coating for outdoor applications.
Knives are practical workpieces, each one having a specific function. The coating you apply, apart from being a significant aesthetic component, can make a positive difference in the performance and the working lifespan of your knife. Careful consideration of what environments and how your knife will be used will help you choose the right blade finishing for your knife.