Le armi eneolitiche di Spessa (Cologna Veneta) e di Gambarella (Povegliano): indagini chimiche e tessiturali.

A halberd and a dagger from Spessa di Cologna Veneta (Verona) and an axe from Gambarella di Povegliano (Verona), all of Eneolithic Age, have been investigated from a compositional and textural point of view utilizing scanning electron microscopy and electron microprobe analysis. The metallographic and textural features of the axe from Gambarella have also been studied by crystallographic analysis performed on neutron diffraction data, using totally non invasive techniques. The three Eneolithic weapons are composed of arsenical bronze, each having different percentages of As. The metal of the two objects found at Spessa show a higher degree of alteration with respect to the Gambarella axe, as is shown by the high porosity of the material, the presence of oxidation areas, and the surface enrichment of veins with a high As content. The composition of the Spessa halberd, made of arsenical bronze with an average As content of 3.4 wt %, is well within the range of the other Eneolithic halberds analysed to date (Gambara, Villafranca, Olmo di Nogara). The composition of the Spessa dagger, made of arsenical bronze with an average As content of 4.1 wt %, is also directly comparable with the compositions of other Eneolithic daggers available to date. The Gambarella axe is made of arsenical bronze with a lower As content with respect to the other two objects (1.3 wt %), it shows a rather homogeneous and compact α phase, and the material has undergone negligible alteration. Most Eneolithic axes are made of pure copper having very minor quantities of other elements (As, Ag, Sn, Fe, Pb), commonly below the 0.5 wt % content. Higher As contents such as the one observed in the Gambarella axe may be found only in the Remedello T.4 and T.62 axes, and in a number of Austrian and German Eneolithic axes. From a technological point of view, the solid solution α phase, which makes the bronze alloy hard, is the predominant crystal phase in all three objects. The fragile γ phase, which makes the objects difficult to cold-work, is not present in the materials, so that all three objects have a high degree of workability and hardness. Accordingly, the crystallographic texture analysis of the Gambarella axe shows that after mold casting the axe was substantially cold-worked along two almost perpendicular directions in order to shape it into the final form. The softening thermal recrystallization process observed in most prehistoric axes is not present in the Gambarella axe.