Knives, silverware, pots, and pans can all rust if they are made of steel. Don’t worry, the rust is not dangerous and you can still safely use the knife. The only issue with rusted knives is that it is unsightly and can add impurities to your food preparation. Also, if rust is not treated, it can end up making a knife unusable.
Let’s take a moment first to understand what rust and corrosion really mean.
What is rust?
Rust, typically referred to as oxidation, occurs when metal or mostly iron alloys that contain iron, such as steel, are exposed to oxygen, humidity, or water for a long period of time.
Rust is formed when the iron undergoes the natural process of oxidation but not all sorts and instances of oxidation form rust. As stated above, only iron or alloys that are made up of iron can rust, but most other metals can corrode in a much similar fashion.
What is Corrosion?
Corrosion happens when an element that loses its electrons (like quite a few metals) combines with an element that tends to absorb extra electrons (mostly oxygen) and then comes into direction contact with an electrolyte solution (mostly water). The role of the water in the process of corrosion is to accelerate the ongoing flow of electron from the metal and to the oxygen.
This process is technically called a redox reaction and is actually two different chemical processes that happen simultaneously: reduction and oxidation.
What is reduction?
Reduction is a chemcial reaction that happens when a molecule gains an electron. Thisi s therole oxygen plays in metal corrosion.
What is oxidation?
Technically, oxidation is the stark opposite of reduction and is the chemcial reaction that happens when a molecule loses an electron. This the primary role of the metal in metal corrosion. Rust and the patina i.e., the absurd green color of copper are the most noticeable results of the metal losing its electrons to the air.
Types of Steels and How they Rust
Steel is divided into two general categories: stainless and carbon. Carbon steel is made up of mostly iron with a small percentage of carbon and a few other metals. Stainless steel is made up of iron, chromium (about 15%), carbon, and a few other metals. The chromium surrounds the iron and protects it from being oxidized by oxygen. However, chromium reduces the durability of the blade–it’ll need to be sharpened more often than carbon steel.
Stainless steel is more resistant to rust than carbon steel but it does not mean that it is rust-proof. It can withstand moisture more than carbon steel but, with severe misuse, it can still rust. Only titanium and ceramic knives are 100% rust proof since they do not contain iron.
Do Copper, Iron and Aluminum Rust?
Technically speaking, only iron and alloys that are made up of iron can rust. Most other metals, including precious ones such as silver and gold, can corrode in quite a similar way.
What sets certain metals apart and distinguishes them from the other metals is mostly the duration of time it takes for the metal to start rusting or corroding.
Let’s take a look at the most common metals and how they try to fight off corrosion and rust!
Does Copper Rust?
Typically, copper does not rust, but it does corrode. Copper is a naturally brown substance and turns a shade of bright and vibrant green as it corrodes. When some might argue that copper’s reaction is simply tarnish rather than oxidation, either way, the metal still undergoes a similar ‘rusting’ process.
In a natural surrounding or environment, copper is typically highly reluctant to corrode. The type of corrosion that finally breaks copper drinking pipes is known as erosion corrosion and it only happens due to exposure to flowing and highly pressured water over a period of time.
Typically seen on old coins, the famous and pretty green ‘patina’ can usually take up to 20 years to completely form.
It is known to be one of them few metals that occur naturally as a directly usable metal in our nature, as opposed to being mined from an ore like most other metals that we use. Copper is also a very soft and easy metal or work with and customize which has led it to being one of the first metals that mankind worked with and created objects out of.
I’m sure you have all heard of the Copper Age, haven’t you? This just goes to show how big of a deal copper was.
Copper is also an excellent conductor of heat and electricity, and it is commonly used in electrical wiring for this property.
Copper is also really low in the reactivity series, a tool in the field of chemistry that is a progression of metals placed from highest to lowest reactivity to acids, extraction of metals from their ores, water, and various other reactions.
Due to its low reactivity, a particular alloy of copper (with 90% copper and 10% nickel) is being used for making parts of boats that will be in contact with seawater, or as pipes to transport drinking water. If you try and look around your house or apartment building, you will most likely notice that many of the appliances use copper pipes to move water.
According to the US Dept. of Housing and Urban Development, the average copper pipe should ideally last 50-70 years.
Does Iron Rust?
Iron does rust, and it does so pretty well. Like we mentioned above, only iron and alloys containing iron can truly rust.
When compared to the corrosion resistance of other metals, iron rusts comparatively faster, especially if it exposed to oxygen and water. In fact, when iron is exposed to brought under direct contact with water and oxygen, it can start rusting within a couple of hours.
Iron will rust quickly if it exposed to high temperatures. Extremely high temperatures can alter or modify iron’s chemical makeup which is highly prone to recombining with oxygen in the environment.
Does Aluminum Rust?
Aluminium is one of the highly used metals used globally and it is quite famous for not rusting. Aluminium does not rust in any way, only iron’s particular oxidation is called rust and we do not use iron when creating aluminium. But it is essential to keep in mind that like most metals, aluminium is susceptible to corrosion as well.
Aluminium is created in 3 distinctive stages:
- Stage 1 – Mining
- Stage 2 – Processing
- Stage 3 – Electrolytic reduction which creates the final product known as aluminium
Aluminium originates from a mineral called bauxite which is usually found in sub-tropical places such as Africa, South America, West Indies, and Australia along with a few recently found deposts in other places such as Europe. Australia is the currently the largest producer of bauxite by supplying nearly 23% of the entire’s world’s production.
This bauxite is eventually processed into aluminium oxide, which mainly just consists of atoms of aluminium and oxygen bonded to each other.
After this, an electrical current is passed through the aluminium oxide which separates the different components from each other. Oxygen bubbles start forming at one end, and pure aluminium droplets start collecting at the other end.
About 4-5 tonnes of bauxite is processed into 2 tonnes of aluminium oxide which then creates nearly 1 ton of pure aluminium.
Aluminium corrdes way slower than most metals like iron. According to a study conducted by Stanford, the main reason why aluminium does not corrode as easily and fast as most metals is because of the special reaction it has with water.
Typically, when water comes into direct contact with metal it pushes the metal to give up its electrons even faster to the oxygen surrounding it.
Aluminium has a rather special reaction with water. When aluminium is exposed to water, the aluminium and the oxygen atoms (contained within the metal – not the oxygen in the air surrounding it) move further away from each other.
They can end up nearly 50% further apart from each other as compared to when they started. This particular reaction of moving apart alters the molecular struction of the aluminium just enough that so that it becomes chemically inert, which means that it would not corrode easily.
How to Prevent Rusting on Knives
Do not wash your knives, pots, pans, and good silverware in the dishwasher. The extreme heat will cause the metal to expand and contract, causing stress points that can become the seeds to rust.
Wash your knives after each use and dry them off. The oxygen in water can easily bond to the iron and this is the most common source of rust.
Avoid salt water. If you are going to work in a salt water environment, use a titanium or ceramic knife.
Once a knife has rust, the rust can be removed but the knife will always re-rust in the same spots. It is best to prevent rust since removing rust is only a temporary situation.
How to Remove Rust from Knives
With Lemon Juice
Let the salt and lemon mixture soak into the tool for nearly two hours. After this, scrub the tool with a lemon rind, and in case the spots are extremely stubborn, use a steel wool or a wire brush. Wash off the lemon, salt, and rust residue with warm water and dish soap and the dry thoroughly.
If there are any rusted spots remaining, repeat this process and soak the tools much longer. Once all the rust has been scrubbed off and removed, clean the tools with dish soap and water and then dry it thoroughly.
Remove Rust With Dish Soap and a Salted Potato
Begin by slicing the potato in half, cover the cut section with drops of dish soap, and then sprinkle a bit of salt or baking soda onto the potato. Salt/baking soda will act as a mild abrasive to facilitate the scarping off of the rust as it dissolves. Rb the rusted area well with the potato to remove rust. Wash and dry thoroughly once done.
Remove Rust With Citric Acid
Begin by adding three tablespoons of citric acid to a bowl of hot or warm water and submerge your rusted metals overnight. The next day, take out the tools and scrubb off the freshly dissolved rust.
Use a Chemical Solution Like Metal Glo to Get Rid of Rust
When cleaning your knives, ensure to rub the chemical solution along with the grain pattern to avoid any scratches from coming onto the metal surface.
Rust is best treated with prevention. Once rusted, a knife is forever scarred. You can remove rust spots by soaking a knife in a non-toxic acid like lemon juice or vinegar. This can be used on all types of knives from machetes to pink pocket knives.