Prehistoric technology Ground and polished stone tools continued to be created and used during the Neolithic period. Numeric record keeping evolved from a system of counting using small clay tokens that began in Sumer about 8000 BC. The Stone Age developed into the Bronze Age after the Neolithic Revolution. The Neolithic Revolution involved radical changes in agricultural technology which included development of agriculture, animal domestication, and the adoption of permanent settlements. The Bronze Age is characterised by metal smelting of copper and its alloy bronze, an alloy of tin and copper, to create implements and weapons. Polished stone tools continued to be
Chinese sun and moon mirrors most (1 part tin per 1 part copper) for "metallic mirrors", namely, the "jiànsuì" 鑒燧 "mirror-igniter" alloy (Hirth 1907: 217-218). However, these ratios are based on Chinese numerology instead of practical metallurgy. Beyond about 32% the alloy becomes excessively brittle, and increasing tin content brings no further advantages of any kind; this the Han metallurgists evidently knew. Indeed they knew much more, for they almost always added up to 9% of lead, a constituent which greatly improved the casting properties. Han specular metal is truly white, reflects without tinning or silvering, resists scratching and corrosion well, and was admirably adapted