January 25, 2022
What is "Kama-yaki", the technique of rust prevention for Nambu cast iron kettles (Tetsubin)?
In 1884, iron kettles were buried during a big fire in the city of Morioka. The kettles had changed and did not rust easily. They say that artisans of the time noticed that feature and applied it as a technique of rust prevention. And this became the basis under which "kama-yaki", a characteristic of Nambu iron kettles, was discovered.
If you remove an iron kettle from its mold and bake it at a high temperature of 800 - 1,000 degrees Celsius, a film called an "oxide layer" will cover the surface. In Japan, we call the oxide layer by its popular name "Kuro-sabi(black rust)". Even though we call it "black," it is not pitch black. It is a variety of rust. When you start to use the kettle, it will be difficult for red rust to occur over the surface.
Scientifically, red rust is represented as "Fe2O3," and black rust is represented as "Fe3O4."
We advise you not to use a scrubbing brush or such to scrub the inside of an iron kettle. The reason is for you to use the kettle without removing the oxide layer.