Around 1602, Vincenzo Casciorola of Bologna, discovered a translucent mineral in fields near Monte Paterna, some 4 miles from Bologna, which when calcined acquired the property of glowing in the dark after exposure to sunlight. Casciorola originally called it the 'lapis solaris' as it appeared to store the light of the Sun. An account was later published by Fortunio Liceti Litheosphorus, sive de lapide Bononiensi lucem, Utino,1640.
This substance appears to be barium sulphide. It was made phosphorescent by being powdered very finely, calcined, then mixed with water or white of egg and fashioned into small tablets, which were again calcined at a high temperature in a furnace using bellows. It then was capable of phosphorescing after being exposed to sunlight. It was called the 'lapis illuminabilis' and attracted the interest of Athanasius Kircher.
There were various kinds of this stone, some glowed like the embers of a fire, others with the characteristic blue flame of burning sulphur.
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