*Kobold refers to mythical goblins who live underground who are “about the size of children”, dress as a medieval silver miners, and mimic the labor of human miners; sometimes by engaging in futile acts of labor such as pouring rocks back and forth between two buckets, or sometimes more sinisterly, causing cave-ins, explosions, or gas poisonings during the ore smelting process.  
Written and artistic accounts of Mine Kobolds date back to around 13th century Europe, with a proliferation in the 15th and 16th centuries, particularly in Saxony and Bohemia (modern-day Germany and Czech) as well as in Scandinavia. Both were centres of silver, copper, nickel, and tin mining at the time, and later of cobalt mining.  

The mineral Cobalt and the color Cobalt Blue were both named after the Kobold. 
Early miners would often mistake cobalt-arsenic compound ores for silver ore. When these ores were smelted, rather than being left with pure silver metal, the heat would cause the release of the arsenic in the form of poisonous gas, while the remaining material was a dull grey brittle metal. These “deceptive” ores were known as “Kobold ore” and were found produce bright, luminous blue-coloured glass and a coveted blue glaze for ceramics. It did not become a paint pigment until 1802, after Swedish chemist became the first to isolate and identify cobalt as a metal 1742.