Raw Glass 

    Manching, Germany      This large piece of purple raw glass was excavated from the Manching Oppida, located on the south bank of the Danube river in Germany.  Many other pieces of raw glass were also found on the site, including opaque yellow and translucent blue chunks.1  Glass is usually manufactured from a mixture of oxides:  ~60% Silica combined with lime, soda and potash.  The addition of manganese results in the purple glass to the right; cobalt results in blue, and yellow was achieved by adding lead oxide.  The silica in the mixture was typically derived from pulverized quartz or sand quartz.  These ingredients were placed in earthenware crucibles and heated in kilns to their melting points to create glass.2
    The Oppida of Manching was populated by 5,000-10,000 people in its heyday.3    It is well known as a production center for glass bracelets.  Due to the availability of certain ingredients for the manufacture of differing glass colors, some raw glass must have been imported.  Scholars suggest that raw glass used for this production was imported from more southern regions.  According to Rupert Gebhard, "500 kg of cobalt blue raw glass discovered in a Greek ship wreck near Corsica was similar to glass used in central Europe [and of that found in the Manching Oppida]."4
    Evidence for the importation of raw glass has been found in other places than the Manching oppida.  In excavations at Hengistbury Head in southern Britain, Bushe-Fox and St George Gray discovered, "lumps of purple glass of a type which had been coloured with manganese salts and contained a high percentage of tin."5  Given these compounds there is a high probability that this glass was imported from the continent.6  The discovery of raw glass at a site, not only points to the aspect of importation, but more importantly and more obviously hints at the presence of some type of glass production.  In the case of Hengistbury Head, fragments of finished purple bracelets were also found during the excavation.

1.  Gebhard I plate: 61
2.  Guido pgs. 7-9
3.  Gebhard II pg. 112
4.Gebhard II pg. 112
5.  Cunliffe pg.  42
6.Cunliffe pg.  43