Many knife makers choose to blacken their blades for a number of reasons. Firstly, it adds an element of style to the knife and can also be used to enhance stealth.
A black coating on a steel blade can also be useful for shielding the metal from corrosion. This is often the case with rust-resistant stainless steels such as those found in military kits.
Stainless steel
Stainless steel is one of the most commonly used metals in many industries. It is resistant to corrosion, moisture, and acidic foods, and it’s easy to clean.
Generally, the chromium content of stainless steel helps it to resist rust and maintain its shiny appearance. The addition of chromium in stainless steel also makes it more flexible and absorbs impact better than carbon steel.
However, like carbon steel, oxidation can leave unsightly stains on stainless steel blades. It’s not a good idea to allow this oxidation to build up on your knife blade, as it will eventually form rust and speed up the deterioration of the metal.
To blacken a blade, first thoroughly clean it with acetone to remove any oil spots that might be present. Then, place it in a cup or glass of acidic solution and wait for the blade to darken. Periodically rinse it off and check the oxidation level.
Carbon steel
Carbon steel is a very hard and durable type of metal used to make knife blades. This material has a high carbon content that makes it sharper and harder than stainless steel, and also helps the knife hold an edge for longer.
Over time, a carbon steel knife will develop a patina that changes the color from grey to black. This is a natural oxidation process that happens when the iron atoms in a blade interact with oxygen in air or water.
It can take a long time for this to happen. This is why it’s important to regularly clean your carbon steel knife after use and to keep it dry.
However, if you are impatient, there are ways to speed up this process. There are wire brushes, fine steel wool, and harsh chemicals that can be used to remove the discolouration quickly. Just be sure to use the right sandpaper or polish. Avoid using cheap sandpaper or polishing compounds as these will ruin the original finish of your knife and can cause it to become even more dull.
Ferric chloride
A lot of knife makers use a chemical called ferric chloride to blacken the blades they make. This chemical is made from iron (III) chloride and works to darken steel by oxidizing it.
The process is a bit messy, but it can make some of the most interesting and visually appealing knives that are out there. You can buy this chemical at most knife makers’ supply stores and soak your steel in it for a specified amount of time.
The chemical is corrosive to the eyes and skin so it needs to be handled carefully. It can also be very toxic if you inhale dust. Wearing a mask can help to prevent this. It is also a good idea to wear gloves and safety glasses when working with this material. It can also irritate your throat and can cause coughing or difficult breathing. Prolonged exposure can even be fatal.
Citric acid
Citric acid is one of the most popular food preservatives and flavoring additives. It is also used in medicine, cosmetics and as a cleaning product.
It is a colorless, weak acid that occurs naturally in citrus fruits. It is an intermediate in a biochemical process called the citric acid cycle, which is important for all respiring organisms.
In cooking, it increases the acidity level of foods like canned tomatoes and berries. It also works well as a natural preservative to help protect food from bacterial growth.
For this reason, it is used to make a variety of foods like canned tomato paste and pickles. It also is used in some cheeses to create a tangy, sour flavor.
You can use a combination of citric acid and ferric chloride to blacken your knife blade. However, you must handle this chemical carefully to avoid burns on your skin or eyes.