Why Did Glass become Blue

Why did the glass become blue. No one knew. The answer came with the discovery of the element cobalt 

Back in Sweden Geoig Brandt was employed in 1727 at the Laboratorium Chymicum, stiU as the holder of a scholarship but in fact as the laboratory manager. Not until 1748 was he formally appointed manager of the laboratory with the duty to analyze different ores and make chemical experiments of 

Henrik ShefFer, Anton von Swab, Sven Rinman, Daniel Tilas, Bengl Qvist and Gustaf von Engestrom, many of whom later became famous scientists. 

There are six kinds of metals and I have shown in my dissertation on the half-metals which I presented to the Royal Academy of Sciences in 1735 that there are also six kinds of half-metalsb. The same dissertation shows that, through my experiments, I had the good fortune to. .. be the first discoverer of a new half-metal namely cobalt regulus, which had formerly been confused with bismuth. 

1) The six half-metals were according to Brandt mercury, bismuth, zinc, antimony, arsenic, and 

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