Cobalt glass—known as "smalt" when ground as a pigment—is a deep blue coloured glass prepared by including a cobalt compound, typically cobalt oxide or cobalt carbonate, in a glass melt. Cobalt is a very intense colouring agent and very little is required to show a noticeable amount of colour.
Cobalt glass for decoration
Regulation cobalt blue olive oil tasting glass with watch glass cover
Ming dish, with smalt blue decoration
Late Roman (circa 4th century AD) finger ring with blue glass intaglio of the figure of Victory
Cobalt is a chemical element; it has symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, produced by reductive smelting, is a hard, lustrous, silvery metal.
Cobalt
A block of electrolytically refined cobalt (99.9% purity) cut from a large plate
Cobalt(II) chloride hexahydrate
Early Chinese blue and white porcelain, manufactured c. 1335