How were cobalt-containing ores used before cobalt was identified as a metal?

Long before cobalt was identified as a metal in 1742 by the Swedish chemist Georg Brandt, cobalt-containing ores were valued primarily for their ability to impart a distinct blue color to glass, ceramics, and enamels.12

These compounds were used as pigments as early as the 3rd millennium BCE, appearing in Egyptian statuettes, Persian necklace beads, and later in Pompeii glass and Chinese porcelain. By the 16th century, a deep blue pigment known as smalt—produced by melting cobalt oxide with silica and potassium carbonate—became a significant industrial application.1234

During this period, miners often viewed these ores with suspicion. German miners referred to them as kobold (after a mischievous household elf), believing the ores were worthless or that goblins had spoiled their silver deposits, as the arsenic-bearing ores were often toxic and difficult to process. It was not until the 18th century that the blue coloration was scientifically attributed to the presence of the element cobalt.512