「No.2」 Let us talk about the anti-rust technology of metal products used in our daily life.
There may be many people who do have industrial images such as automobile parts, steel products, and buildings, when asked about anti-rust.
However, “Rust prevention technology” is used for many of our familiar metal products.
There are many metallic products that are hard to rust, such as stainless steel made products and enamel processed materials used particularly in kitchens and other goods. The Rust prevention technology used for these products was achieved by the development of the modern science. The rust prevention technology has been used in Japan since older age.
Let us talk about rust prevention technology used in the “NAMBU Ironware”, which is one of the traditional crafts in Japan.
Anti-rust technology used for the NAMBU Ironware
The NAMBU Ironware (mainly TETSUBIN, Cast iron kettle) has a “surface treatment” process, called “Metallic taste stop”. At first, melted iron is poured into the mold and then the iron has been cooled down. Then, “Metallic taste stop” process is taken.
The “Metallic taste stop” is a treatment to harden the iron under 800 ~ 1000℃ in the charcoal furnace, and this process creates “oxide film that is insoluble in water” on the entire surface of iron, so that it becomes a strong iron product difficult to rust.
However, the oxide film made in this “Metallic taste stop” process is not versatile. By rubbing or scraping the surface of the oxide film, the innocent iron beneath the film becomes exposed, which part leads to rust.
therefore, careful attention shall be paid when start to use or in use the NAMBU Ironware.
Here, let us introduce two methods recommended by the beginning of the use of the NAMBU Ironware.
The first method is to boil water with the NAMBU Ironware several times in the beginning of use and throw away the boiled water. As a result, the amount of calcium, contained in tap water, adheres to the iron surface and prevents rust by coating the defective part of the oxide film with the calcium. Calcium is one of the minerals and this is suggested as a method of boiling hard water which have a large amount of mineral content.
The second method is to put the tea leaves and boil them. By boiling with tea leaves, the components of the tannin contained in the tea leaves react with iron to produce “iron salt”, which prevent rust by burying the defective part of the oxide film in the same manner as the first method.
Both calcium and tannin-iron salts have a property that does not dissolve in water and maintain a strong state against rust on the inside of the TETSUBIN.
In other words, “oxide film”, created by Metallic taste stop process, “adhesion of calcium”, “tannin-iron salt”, as “anti-rust coating”, are effectively changing to strong product that is resistant to rust by “anti-rust technology”