Cobalt compounds are widely used in the ceramic industry as blue coloring agents. This is due to the stable and brilliant blue color of cobalt silicate. Generally, cobalt oxide is used, but other compounds are also used, and once oxide is formed during firing, silicates are formed to produce blue. Gosu, in other words, is natural cobalt with various impurities. Once, when European miners believed in the existence of so-called “earth gods” in the earth, they discovered an ore in the Prussian province of Saxony that was as heavy and shiny as true silver, but no matter how it was refined, it did not produce any silver, but only a slight grayish ash and a foul odor like leek. It was then discovered that the ore had been used in a mysterious machine by a mysterious demon. The name “kobold,” meaning “earth god” or “devil,” was given to it, and the mineral was discarded and neglected during mining. Later, this use was discovered, and it was first used in pottery production at the government pottery in Meissen around 1720, where it has been widely used for several decades since. It is currently the most widely prized blue pigment and other pigments in the ceramic industry. In Japan, Zuihoya Uzaburo brought it from France for the first time in 1867 (Keio 3), and it was highly prized as a blue pigment for dyeing because of its extremely brilliant coloration, and Chinese gouze and sand glaze, which are made of natural cobalt, were no longer used. Around the end of the Taisho period (1912-1926), cobalt oxide was considered too monotonous to match the elegance of natural cobalt, and various synthetic materials were introduced.
