Wikipedia
Cobalt glass—known as "smalt" when ground as a pigment—is a deep blue colored glass prepared by including a cobalt compound, typically cobalt oxide or cobalt carbonate, in a glass melt. Cobalt is a very intense glass colorant and very little is required to show a noticeable amount of color. Cobalt blue glass 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.
Cobalt glass such as Bristol blue glass is popular with collectors, and is used in the distinctive blue bottles of Harvey's Bristol Cream sherry. It is appreciated for its attractive color.
Usage examples of "cobalt glass".
She nodded, directing her gaze at the cobalt glass, willing her eyes to stop welling up.
Rani followed her to the trunks, trying to remember to breathe, trying to plumb the deep power of the cobalt glass, trying to hold on to the endless peace of Speaking.