4 The Bronze e Age Chalcolithic man was clearly aware of the many useful features of copper that made it preferable to stone or organic materials for some specialized applications.Among these properties were its elasticity and particularly plasticity,which allowed sheets or chunks of copper to be given useful shapes.Chalcolithic man also exploited the fact that copper hardens during hammering,that is,as a result of plastic deformation.Last but not least,molten copper can be cast into molds to obtain more intricate shapes. On the negative side,surface oxidation and gases trapped dur- ing melting and casting which may form porosity were probably of some concern to Chalcolithic man.More importantly,how- ever,cast copper is quite soft and thus could hardly be used for strong weapons or tools.Eventually,the time had come for a change through innovation.A new material had to be found.This material was bronze;see Fig.4.1. It is not known whether Chalcolithic man discovered by ex- perimentation or by chance that certain metallic additions to cop- per considerably improved the hardness of the cast alloy.(An al- loy is a combination of several metals.)In other words,cast bronze has a higher hardness than pure copper without necessi- tating subsequent hammering.Further,it had probably not es- caped the attention of Chalcolithic man that the melting tem- perature of certain copper alloys is remarkably reduced compared to pure copper (by about 100C as we know today) and that molten alloys flow more easily during casting. Naturally,some impurities that were already present in the copper ore transferred into the solidified copper.Among them were arsenic,antimony,silver,lead,iron,bismuth,and occa- sionally even tin.These impurities,however,were not present in sufficient quantities that one could refer to the resulting product as an alloy.Small quantities of these impurities rarely change4 Chalcolithic man was clearly aware of the many useful features of copper that made it preferable to stone or organic materials for some specialized applications. Among these properties were its elasticity and particularly plasticity, which allowed sheets or chunks of copper to be given useful shapes. Chalcolithic man also exploited the fact that copper hardens during hammering, that is, as a result of plastic deformation. Last but not least, molten copper can be cast into molds to obtain more intricate shapes. On the negative side, surface oxidation and gases trapped dur￾ing melting and casting which may form porosity were probably of some concern to Chalcolithic man. More importantly, how￾ever, cast copper is quite soft and thus could hardly be used for strong weapons or tools. Eventually, the time had come for a change through innovation. A new material had to be found. This material was bronze; see Fig. 4.1. It is not known whether Chalcolithic man discovered by ex￾perimentation or by chance that certain metallic additions to cop￾per considerably improved the hardness of the cast alloy. (An al￾loy is a combination of several metals.) In other words, cast bronze has a higher hardness than pure copper without necessi￾tating subsequent hammering. Further, it had probably not es￾caped the attention of Chalcolithic man that the melting tem￾perature of certain copper alloys is remarkably reduced compared to pure copper (by about 100°C as we know today) and that molten alloys flow more easily during casting. Naturally, some impurities that were already present in the copper ore transferred into the solidified copper. Among them were arsenic, antimony, silver, lead, iron, bismuth, and occa￾sionally even tin. These impurities, however, were not present in sufficient quantities that one could refer to the resulting product as an alloy. Small quantities of these impurities rarely change The Bronze Age