Cobalt Blue Glass
from the
Glass Encyclopedia

Cobalt blue glass is normally a deep rich blue like the vase on the left. It is made by incorporating cobalt oxide in the molten glass mixture.

Most blue glass is given its color either from cobalt oxide or from copper oxide added to the molten glass. Copper is a more delicate colorant than cobalt. It only requires a small amount of cobalt oxide to produce a deep rich blue.

Cobalt is a metal, found in copper and nickel ores in many countries, but mined cheifly in Africa, USSR, Australia, Canada and smaller amounts in other countries. It was discovered by a Swedish chemist, Georg Brandt, in 1742; although the coloring properties of the ore has been known since very ancient times. There was even one piece of cobalt blue glass in Tut-Ankh-Amen's tomb in Egypt.

Before the 1920s the world's production of cobalt was primarily used as a glass and ceramic colorant. Since then it has been used increasingly in metal alloys, and over 80% of today's production of cobalt is used as a metal, - it is, for example, a component of the best magnets. Surprisingly it also makes up 4.3% of vitamin B12.

Small amounts of cobalt (around 1 ounce per ton of glass) are used to neutralise the yellow tint of iron in glass such as window glass. To produce a blue colour in glass, you only need to add five ounces to a ton of glass. Deeper blues are obtained by adding up to ten pounds of cobalt oxide to a ton of glass. This deep blue glass can then be ground up into a powder called "SMALT" which is used as a coloring agent for enamel, for glazes on pottery, and for making more blue glass.

Whilst cobalt oxide produces a deep royal blue, there are other compounds of cobalt which produce different colors. Cobalt aluminate makes turquoise glass; cobalt silicate produces violet-blue glass. Cobalt oxide added to borosilicate glass produces a purple or red glass.

There are many famous types of blue-colored glass which are in fact cobalt blue glass. Bristol Blue is one of the most famous. Fenton's blue carnival glass is a cobalt blue. So is Fenton's Royal Blue and Periwinkle Blue (both from the 1930s), their Blue Silvertone in the Sheffield pattern and Velva Blue from 1981. The Cambridge Glass Company used cobalt for their Royal Blue and their Moonlight Blue. Heisey called their cobalt blue "Steigel Blue"; and Fostoria produced two cobalt blues which they called "Regal Blue" and "Azure Blue".