Excerpt from Bulletin of the Minnesota Academy of Science, Vol. 5
Some of it apparently is pulverized bort or diamond dust, freed from impurities so as to leave the glass clear or translucent. These earliest specimens are found in the ruins of the Это и многое другое вы найдете в книге Bulletin of the Minnesota Academy of Science, Vol. 5 (Classic Reprint) (Minnesota Academy of Sciences)