Cobalt blue glass is a deep blue colored glass prepared by adding cobalt compounds to the molten glass. It is appreciated for its attractive color and 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, the cobalt glass has twice the effect.
While the silica glass is molten, a modest amount of Cobalt oxide is added to the glass – the color is quite consistent – and the color is nearly independent upon the amount of Cobalt Oxide added. Naturally, molten glass is an oranges yellow when hot and the true color cannot be seen until the glass has gone through a quasi-static cooling process.
Many people collect objects made from cobalt blue glass, amassing large collections. One popular example of cobalt blue style glass is Bristol blue glass, as in the distinctive blue bottles of Cream sherry. It is also a little known fact that Cobalt glass changes the color of hydrochloric acid in a mixture of multi-colored cations.
Modern day cobalt glass is nearly identical to Blue light glasses antique or historical blue glass, so it can be quite difficult to discern true antique cobalt blue from newer glass. Look for markings on the bottom of the glassware that may indicate age – often times former manufacturers and former makers of this glass marked it with a symbol such as an ‘H’ inside a diamond (for the former Heisey glass) or a ‘C’ inside a triangle (for the former Cambridge glass). Newer cobalt glass may be marked with a ‘B’ inside a diamond or a ‘B’ inside a triangle. As a side note, Bennet glass stopped production in the early 1980’s and many of the glass moulds were sold off.
Cobalt blue style glass and glassware can be fun to collect – try to choose pieces of glass with no flaws or minimal flaws. Keep away from glassware that has chips, cracks or other obvious issues as these problems will significantly depreciate the value. Also look for markings on the glass to help identify the maker or age of the glass. Most of all, have fun collecting the glass and try to display the glass in windows or with a good back lighting. You will receive many years of joy collecting this glass and it is sure to appreciate in value.