Why are there marks on my new knife? It may come as a shock to some to find stains and marks on your new expensive knife. So what are they and why do they appear? One of the most common questions we get asked following the purchase of a new Japanese chef knife are the dark marks that can appear on high carbon steel blades. These marks don’t wash away, and can result in discolouration that lasts for the life of the blade. Here, we’ll explain here the process behind a patina and how it can actually be beneficial. What is a Patina? A patina in short is the discolouration or ‘aged’ look of a steel that lacks stainless steel elements (mainly chromium), which shows in shades of yellow, blue and grey. There are particular types of steel that will show up a patina much faster than others, in different colours, as each steel has a different combination of elements. For example a patina will not only develop on steels such as Aogami and Shirogami, but also on copper and bronze which will show in shades of green and blue. These steel types will not only show a patina, but due to their lack of stainless properties, they can also develop rust spots if not kept dry between uses. What causes it? The main causes of a patina forming likely occur from the first use of your blade. These are moisture, acid, and salts. The acidity of citrus and the moisture of proteins will both cause different markings on the blade to form, all of these are unavoidable. There have been many instances of Japanese knives on display being touched by bare hands, and the moisture from fingerprints when unwiped afterwards, can cause patina or rust spots to form. How is it a good thing? Once a patina has been formed on your Japanese knife, it acts like a seal, and can actually protect the steel underneath from rusting. While your knife may not look the way it was when it was brand new, it is uniquely yours and carries with it the marks of many meals prepared. Why aren’t all blades stainless steel? Wouldn’t that be easier? Easier to maintain? Yes. Beneficial for all purposes? No. Stainless steel blades can be used in a much more carefree manner, as they are often softer steels which take more punishment, do not discolour, and can be left wet for longer without having rust appear. However, a high-carbon steel Japanese chef knife can be hardened to a higher hardness (HRC), contains more carbon and other strengthening elements, and as such will have an edge that stays much sharper for longer. For a chef that uses his knives day in and day out, not having to sharpen his blades every couple of days can be hugely beneficial, with the trade off being they must be wiped down between uses. There are however, exotic steel types that exist (SG2/R2, ZDP-189) that combine the high-carbon, long lasting edge retention with the high stainless elements that create knives with incredible performance and almost zero maintenance. These knives can only be made by skilled craftsman, and the steels are often expensive to procure and difficult to work with. Can I remove a Patina? A patina can be removed using a knife polishing compound, or by using a whetstone to remove some steel off the affected area of the blade. This is a process that one must be competent in to accomplish properly. It is however likely that the knife will just develop another patina straight after it’s first use anyway. How do I control rust? Rust spots can form minutes after a blade is left wet or with food residue, so the best way to control rust spots on your blade is to wipe your knife down with a clean cloth after use, keep them dry, and stored away from any sources of moisture or salt. A patina is an unavoidable result of purchasing a high-carbon steel knife, but with a little care and maintenance, can be a protector of your knife to ensure it’s prolonged use.

Japanese chef knives need a little more care than your regular off the shelf knives. But don’t be afraid, looking after them is easier than you think. So you’ve taken the plunge and bought your first ‘real’ chef knife. As you gaze at it with a smile, it can be somewhat daunting to use your Japanese chef knife for the first time. As with all high-performance tools, your new knife will need some love and care to ensure it performs to the highest level for many years to come. The blades construction and steel type will determine the level of care required, as the higher carbon steel Japanese chef knives require more attention than others. The main question we get when someone new to carbon steel (Blue/White) knives uses theirs for the first time is one of shock being, “Why has my blade changed colour?!” High-carbon steel Japanese chef knives (whether clad in a stainless steel or not) are knives that do not contain any (or very little) Chromium, the main element that give stainless knives their rust resistance. As such, these blades are prone to oxidation or discolouring from the first use. Fear not, as the patina is only superficial, and will actually help prevent against rust in the long term. Certain foods like meats, acidic fruits and vegetables, and also condiments like mustard will all produce wildly different colours and patterns as they emerge and leave their mark on your blade. This is completely normal, and is all part and parcel of owning a carbon steel knife. Cutting When cutting using your new knife, ensure that only a straight up/down motion is used, as these knives use an extremely hard steel with a very fine edge. Any twisting or torquing of this extremely thin steel will chip or break your blade. Certain food textures (chicken, meat etc) will sometimes not respond to cuts whereby your press directly down onto the food with the blade. Try either a push or pull motion to ensure effortless cuts. We advise to only cut on wooden boards! There is conjecture as to whether plastic boards are safe, but we prefer to err on the side of caution with this one. Due to the softness of some plastic boards, your knife will occasionally sink slightly into the board with each cut. If the blade is twisted or moved at this contact point, damage has been known to occur. It almost goes without saying, please do not use your knife to cut any bones, stoned fruits, or any other hard objects. Washing A soft dishcloth and hot water is all you need to keep your blade clean. Use a small amount of dish soap if desired, but avoid scourers and anything abrasive. Absolutely no dishwasher use! For blades that have a core or are made from a high carbon steel such as Blue, White Steels, these will need to be wiped down immediately as rust spots can develop within minutes as they contain no stainless elements. Storage You new knife deserves better than crashing around in your cutlery drawer, so keep them in the original box it came in. Even better, pick up a leather-clad magnetic knife holder to showcase your knives in the open (away from mischievous pets and children) where they belong. Add a dab of Camellia Oil between uses for carbon steel knives, as this will prevent any moisture reaching the steel and causing rust spots. Sharpening Keeping you new knife sharp may take some practice, so we recommend a whetstone with two side for beginners, one with a rougher grit of 1000 to remove steel from the edge, and then a finer grit like 6000 to polish the edge. We recommend practicing on a cheaper knife first, until you can hone your skills and be confident enough to attempt to sharpen your more expensive knives. We’ll write up a complete sharpening guide soon. For now, there are plenty of great videos on YouTube like this one to quickly pick up the skills required. If you ever need any further information on how to care for your new knife, please reach out via any of the channels available!

It’s the business end of the chef knife, the part that does the real work. The core steel of your knife, or the cutting edge, is one of the most important aspects in determining how your knife performs. The grind, balance, weight and size of a knife are also important, but often the debate rages on what the best core steel is to use for a knife.  Is ZDP-189 worth the cost? Is VG-10 any good? Carbon vs Stainless? Each steel, like each knife type, has its own advantages and disadvantages, but a good knife steel is the foundation from which the rest of the knife is constructed. Generally speaking, you’ll find a Japanese blacksmith will prefer to use a steel type that belongs to one of 3 groups: Traditional High-Carbon Steels (Non Stainless), like Aogami or Shirogami Stainless Steels (VG10, AUS10) Powder Steels (ZDP-189, SG2/R2, Cowry X) We’ll cover the steels in each of these 3 groups and what makes them different from your regular off the shelves. Carbon Steel Japanese blacksmiths prefer to use these traditional knife making steels that lack the stainless elements of their counterparts. Easy to forge to high hardness with good edge retention and excellent sharpness, they are the closest steels to ‘Tamahagane’, the steel ancient samurais used for their swords.  They are, as their name suggests, very high in Carbon (C) content, the element which gives steel its ability to be hardened during the heat treatment process. As steel is hardened it becomes more brittle, a trade-off for it’s long lasting sharpness. Shirogami/White Paper Steel White Steel is known for 2 things: steel purity, and incredible, surgical sharpness.  It has very little added elements, except for trace amounts of Sulfur and Phosphorous. It will rust and patina quite easily, so be sure to wipe down immediately after use, and beware when using a Shirogami knife on things like onions or potatoes, as it can leave orange or brown marks on food. White Steel 1 High hardness, up to 65 HRC. Carbon: 1.25-1.35% Manganese 0.20 – 0.30 % Phosphorus 0.03 % Sulphur 0.004 % Silicon 0.10 – 0.20 % White Steel 2 Moderate hardness, up to 61 HRC. Carbon 1 – 1.15 % Manganese 0.20 – 0.30% Phosphorus 0.03 % Sulphur 0.004% Silicon 0.10 – 0.20 %   Aogami/Blue Paper Steel Probably the most commonly used carbon steel in Japanese chef knives, Aogami or “Blue” paper steel gets its name from the blue paper that Hitachi Metals supplies the steel in. It comes in 3 variants, Blue 1, Blue 2, and Blue Super, who’s incremental carbon increases result in Blue Super being one of the highest hardness knife steels available when quenched and treated well. It is a reactive carbon steel, essentially white steel with added chromium, carbon, and tungsten. This results in a knife that does not rust or patina quite as easily as White Steel, and holds an edge for longer. Blue Steel 1 High hardness, up to 65 HRC. Carbon: 1.25-1.35% Chromium: 0.20-0.50% Manganese 0.20 – 0.30 % Phosphorus 0.03 % Sulphur 0.004 % Silicon 0.10 – 0.20 % Blue Steel 2 Moderate/High Hardness, up to 63 HRC Carbon 1.05 – 1.15 % Chromium 0.20 – 0.50 % Manganese 0.20 – 0.30 % Phosphorus 0.03 %  Sulphur 0.004 % Silicon 0.10 – 0.20 % Tungsten 1.00 – 1.58 % Blue Super High Hardness, up to 65HRC Carbon: 1.40 – 1.50 % Chromium 0.30 – 0.50 % Manganese 0.20 – 0.30 % Molybdenum 0.30 – 0.52 % Phosphorus 0.03 % Sulphur 0.004 % Silicon 0.10-0.20 % Tungsten 2.00 – 2.50 % Vanadium 0.30 – 0.50 % Stainless Steels Often not quite as high in carbon content, stainless steels have added chromium which acts as a protecting element to oxidizing agents such as acidic foods and water. Generally speaking, when a steel has 12% or above in Chromium content, it is regarded as a stainless steel. They can be hardened to about HRC 60, and as such a sharp edge will not last quite as long as their carbon steel counterparts. The main stainless steels used by Japanese blacksmiths are VG-10 and AUS10, and Ginsan. For their versatile nature and minimal maintenance, stainless steels are very common across many knives manufactured throughout the world. VG10 Moderate/Low Hardness, up to 60-61 HRC Carbon: 0.95 – 1.15 % Chromium: 14.50 – 15.5 % Cobalt: 1.30 – 1.50 % Manganese: 0.50 % Molybdenum: 0.90 – 1.20 % Phosphorus: 0.03 % Vanadium: 0.10-0.3 % AUS10 Moderate/Low Hardness, up to 60HRC Carbon: 0.95 – 1.10% Chromium: 13.00 – 14.50% Molybdenum: 0.10 – 0.31% Vanadium: 0.10 – 0.27% Nickel: 0.49% Manganese: 0.50% Silicon: 1.00% Phosphorous: 0.04% Sulfur: 0.03% Ginsan Moderate/High Hardness, up to 63 HRC Carbon: 0.92 – 1.10 % Chromium 13.00 – 14.5 % Manganese (Mn) 0.60 – 1.00 % Phosphorus (P) 0.03 % Sulphur (S) 0.02 %  Silicon (Si) 0.35 % Powder Stainless Steels This is where the real fun begins! Powder steels are exotic modern alloys that combine the high hardness, high strength properties of carbon steels, with added stainless properties, resulting in superior performance in every way. Whilst being slightly harder to sharpen and maintain, a cutting edge made from Powder Stainless steel will hold an edge much longer than most other knife steels. The most common powder steels in japanese knife making are SG2/R2 (Super Gold 2/R2), ZDP189 and HAP40, with ZDP-189 bursting onto the scene in the last decade as being the go-to powder steel of choice for high end chef knives. You’ll find that a knife with a Powder steel core is more expensive than most others, and for good reason! The steels are expensive and extremely hard to procure, and even then, in the hands of an amateur blacksmith, they are useless. It takes an extremely skilled craftsman to forge and laminate these steels together, resulting in longer build times and requiring nothing short of perfection in the manufacturing process. SG2/R2 High Hardness, up to 64 HRC Carbon: 1.25-1.45% Chromium: 14.00 – 16.00 % Molybdenum: 2.30 – 3.30% Vanadium: 1.80 – 2.20 % Manganese: 0.40% Silicon: 0.50% Phosphorous: 0.30%  Sulfur: 0.30% ZDP189 Extremely High Hardness, up to 67 HRC Carbon: 3.00% Chromium: 20.00% Molybdenum: 1.40% Tungsten: 0.60% Vanadium: 0.10% Manganese: 0.50% Silicon: 0.40% HAP40 Extremely High Hardness, up to 68 HRC Carbon: 1.27 – 1.37% Chromium: 3.70% – 4.70% Molybdenum: 4.60 – 5.40% Tungsten: 5.60 – 6.50% Vanadium: 2.80 – 3.30% Cobalt: 7.50 – 8.50% Final Thoughts There you have it. Some information on the most common seen steel types in not only Japanes knives but knives around the world. Be sure to choose a steel that matches your lifestyle and ability to maintain!