Cobalt glass is a deep blue colored glass prepared by adding cobalt compounds to the molten glass. It is appreciated for its attractive color. It is also used as an optical filter in flame tests to filter out the yellow flame caused by the contamination of sodium, and expand the ability to see violet and blue hues. Under fluorescent light, cobalt glass has twice the effect.

Some people collect objects made from cobalt glass, amassing large collections. One popular example of cobalt glass is Bristol blue glass, as in the distinctive blue bottles of Harvey's Bristol Cream sherry. Cobalt glass changes the color of hydrochloric acid in a mixture of multi-colored cations.
[edit] For pigment use

Powdered cobalt glass, called smalt (or also simply cobalt glass), has been historically important as a pigment in painting, pottery, and other media. Cobalt glass and smalt are made from silica and are not the same as cobalt blue, which is colored by cobalt ion is a similar way, but using a melting process with alumina.
[edit] See also

* Smalt
* Cobalt blue
* Cobalt

No element but cobalt gives glass that color.

Bristol glass can be many colors. It is a designation for glass, usually opaque or semi opaque and decorated with enamel. Bristol Blue Glass was and I think still is, made in Bristol for sherry and various other products.

I'm such a lay person when it comes to glass and other vintage/antique things, so usually believe everything I read. You seem very knowledgeable re:antiques/vintage, so i'll take your word. ;o)

Never a truer statement. Wikipedia is really not reliable.
Diane