Fragment of wall and edge of octagonal pipe glass, drinking glass drinking utensils tableware holder soil find glass forest glass, free blown and shaped into blown Fragment of wall and edge of octagonal pipe glass in clear light green glass (forest glass). The wall has diagonally upwardly ribbed pattern of imposed and blown glass threads. octagonal shape is formed during manufacture by inserted octagonal (usually ceramic) mold. The edge is slightly thickened by fusion and has wavy line between the angles archeology underground pit Rotterdam City Triangle Groenendaal archaeological find in the soil Metrotunnelbouw Groenendaal.