Bolognian stone

A full description is given in later editions of the preparation and properties of the Bolognian stone (phosphorescent barium sulphide see Vol. II, p. 334). ... 

In 1603 Vincenzo Cascariolo, an Italian cobbler and amateur alchemist in the countryside near Bologna, made a notable observation. He had found a heavy stone and ground it to a grain size of meal. He mixed the powder with the white of eggs and made cakes of it. These he laid in layers with coal and calcined for 4-5 hours. To his tremendous amazement he found that the calcined stone shone in darkness if it had first been exposed to the sun. It phosphoresced. This mysterious and magical ability to accumulate light and emit it in the dark created a sensation. The substance he had prepared became known as Bolognian Stone. 

Bolognian Stones fascinated J. W. von Goethe, who collected many and examined them in Weimar in 1784. 

The magic stones also found their way to Gahn and his laboratory in Falun. After Scheele s fundamental work with barium, Gahn could rapidly establish that barium was also the main component in Bolognian Stone. Cascariolo had carried out his experiments with barite BaSO,. 

In the actual case of Bolognian Stone, perhaps BaS is formed together with a certain excess of Ba, dissolved interstitially. The stone then behaves like an impure semiconductor, displaying phosphorescence. 

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