Process Words:
Annealing - softening the steel to a more ductile state. This involves heating the blade to a specific temperature and letting it cool very slowly for a lamellar anneal, or several times subcritical with slow cool for a version of a spheriodizing anneal.
Austenite - the crystal structure of iron and steel that forms at high temperatures. The grain size and structure of all other states that steel can be in are determined by this state. All forging and many heat treatment procedures occur when the steel is in this state.
Carbides - hard structures made of carbon and carbide forming elements such as vanadium, tungsten, or chromium that are embedded in the steel matrix. These embedded hard "chunks" increase the wear resistance of the steel.
Decarburization - when steel is heated in an atmosphere that is high in oxygen, carbon diffuses out of the steel surface to bind with the oxygen. Prolonged heating in the wrong atmosphere can remove so much carbon that it ruins the steel to a significant depth into the surface of the blade.
De-tempered - heating up the blade too much so that the hardness of the blade is diminished beyond what is ideal for the piece. Friction from grinding can de-temper the thin edge of a knife, making it too soft to hold a good edge. Knives that have been through fires or other high heat situations can also be de-tempered.
Differential hardening - (note this is different than differential tempering)- where the cutting edge of the blade is hardened but the core or spine of the blade is kept soft to resist breaking under extreme use. Also can generate a visible hamon in some steels.
Differential temper - conceptually similar to differential hardening; however, the whole blade is hardened but then the spine is tempered to a greater degree (tougher, softer) than the edge for increased toughness under extreme use. This is our dominant process as it provides increased blade strength and rigidity over differential hardening.
Forced patina - where we have intentionally soaked blades in an acid, such as vinegar or mustard, to generate a patina for protective or aesthetic purposes.
Forge - place to heat up the metal to work. Must be able to get at least 2,000 degrees F. We currently use propane forges, but Luke's background is in coal/coke forging. Propane forges are friendlier to our neighbors.
Forging - physically molding the steel at very high temperature. We do this by hand and eye with various weights and styles of hammers on an anvil.
Grain size - the size of the crystalline structure of the steel. Smaller grain size means a greater ability to take a finer, sharper edge and increases toughness- small is good, though this logic can be taken too far. Carbide size and distribution is equally important.
Hamon - transition line between hardened and unhardened steel. Typical of Japanese knives and swords, also visible in some of our differentially hardened blades- the product of a specific hardening process.
Hardening - changing the molecular state of steel from soft and ductile to a very different molecular state that is very hard and stressed. Blades at this stage can crack due to internal stress. Hardening is accomplished by quenching in an appropriate viscosity fluid to achieve a specific cooling rate for a given type of steel.
Heat Treatment - the series of steps involved in arranging the molecular and crystalline structure of the steel into the state that you desire it. Heat treatment involves normalizing, thermal cycling, austenitizing, quenching, and tempering.
Martensite - the structure of steel that produces the most hardness. Full transformation of the knife blade to this state is the goal of knifemakers. This structure is body centered tetragonal which is formed by carbon atoms being "trapped" in the iron lattice, forcing the iron atoms apart. This situation induces molecular stress which generates hardness. Martensite when "fresh" is very brittle and must be tempered to make a good blade or tool.
Normalizing - relieving forging stresses and increasing grain consistency, also helps distribute carbon and alloy. A neglected but absolutely critical step in heat treatment.
Patina - Fe2 oxidation layer on the surface of carbon steel. Creates a protective layer barring future, more destructive oxidation (Fe3, rust). Acids such as those in meats or acidic foods quickly add a patina to carbon steel blades.
Quenching - rapidly cooling steel that has been held at a very specific target temperature- typically around 1500 degrees F for many of our steels. Quenching is done in specially designed oils, air, or brine depending on the alloying elements in the given steel. These materials are called the quenchants. Steel "as quenched" is fully hardened.
Rockwell tester - a machine that measures hardness of steel. For hardened steel the Rockwell "C" scale is used, and you will see these measurements denoted as HRC or Rc. The machine places a 150 kg weight on a 120 degree diamond-tipped cone to indent into the steel surface. The depth to which the cone penetrates the steel tells us the hardness of the material.
Tempering - relieving the stress within the steel after hardening to increase toughness. This lowers the hardness of the steel to differing degrees depending on which temperatures, duration or cycles are used.
Thermal Cycling - a series of rapid heating and cooling cycles above and below the A1 temperature (the temperature of austenite transformation) for the alloy. Typically these cycles are done in descending heats. The goals of thermal cycling are to reduce the grain size of the steel, making it tougher, and to prepare the steel for the final austenitization prior to quenching.
Knife Anatomy:
Belly - a deep curve in a blade- very desirable for slicing purposes as it increases edge length per given knife length.
Bevel - the shape of the cutting edge of the blade. The finer/shallower the bevel the more acute the angle and greater cutting efficiency of the blade.
Bolsters - typically metal mini-scales that are attached to the tang at the transition from the blade to the handle. Help with heft and balance.
Distal taper - where the blade tapers in thickness gradually all of the way to the tip. Gives good balance and aesthetics, particularly in kitchen knives.
Full-tang - where the same piece of metal as the blade extends throughout the whole knife and is visible all of the way around. This typically considered stronger than other designs, but this is often a misconception.
Guard - a piece of metal (typically) separating the blade from the handle.
Hidden-tang - where the same piece of metal as the blade is hidden within the various handle materials and typically does not extent the full length of the handle. Very strong (depending on how it's done) and creates less joints where temperature/humidity shrink/swell can cause handle problems. Typically lighter than full-tang knives.
Maker's mark - a stamped or etched mark identifying the maker of the knife. Ours is the double B. We stamp our marks into the hot metal freehand, which is why they're not "perfect" every time. It helps identify the knives as handmade while in no way impacting their function, strength, or utility.
Micarta (TM) - a trademark of Norplex-Micarta high pressure laminates. This material is made of many layers of cloth impregnated with epoxy. Very durable, waterproof, shockproof, and does not shrink or swell. We now make our own phenolic/epoxy laminates similar to Micarta but out of recycled cloth of various types and can do custom handles from cloth or clothing that you supply.
Pommel - a metal piece at the very end of the knife or sword handle.
Scales - the two pieces of handle material that are attached to the sides of full-tang knives.
Spacer - minor handle materials added for aesthetic or functional purposes.
Spine - the top of the blade. Can be plain, rounded, or have filework.
Tapered tang - where the same piece of metal as the blade tapers in thickness from the middle of the knife to the back of the handle. Makes a full-tang knife lighter and can improve balance.