1.The First Materials(Stone Age and Copper-Stone Age) 7 the reduction process.It also aids eventually in the separation of the molten copper from the slag once the melt has cooled down. Specifically,iron ore combines with the unwanted sand particles that just happen to be contained in the ore. The immense heat was accomplished by burning charcoal com- bined with blowing air into the furnace either by mechanically ac- tivated bellows and/or through blow tubes(called tuyeres)(Figure 1.2),or by placing the furnace near the top of a mountain where the updraft winds were utilized.It is still a mystery today how Neolithic man could have found this chain of procedures without a certain degree of intuition or possibly the help of initiates. Archaeo-metallurgists have recently ruled out the hypothesis that copper could have been accidentally formed in campfires whose enclosures may have consisted of copper-ore-containing rocks.The temperatures in campfires(600-700C)are known to be too low for smelting copper and the reducing atmosphere does not persist for a long enough time.(However,lead,which has a lower melting temperature,can be smelted this way from its ore.) It is believed today that the"technology"of copper smelting was probably borrowed from the art of making pottery,which was de- veloped nine or ten thousand years ago or perhaps even earlier at certain locations.Indeed,the oldest known artifact made of baked clay is a fertility figurine called the "Venus of Vestonice,"which was found in the Czech Republic and supposedly dates back to about 23,000 B.c.(see Figure 15.1).In general,however,copper smelting and pottery seem to appear at comparable times in his- tory.Specifically,Neolithic man had observed that mud bricks harden when dried in the sun and soften when again exposed to rain.A deliberate attempt to accelerate the drying process by ex- posing the mud bricks to the heat of a fire probably led to the ob- servation that an irreversible hardening process had occurred.A chemical transformation near 500C causes a permanent consis- tency of clay which makes it water-resistant.It can be reasonably assumed that this observation eventually led to the systematic de- velopment of the art of pottery and the design of kilns instead of drying clay over or under an open fire.Neolithic man must have observed that stacking pots on top of wood fuel and covering this pile with fragments of pottery and earth would increase the tem- perature.Eventually,kilns with permanent walls were developed, parts of which still exist today,dating back to the beginning of the sixth millennium B.C.We shall return to this subject in Chapter 15. Neolithic people have decorated some pottery utilizing proba- bly the same ground-up metal ores(mixed with a lead oxide bind- ing agent)that were used customarily for tribal body painting.Var- ious metal oxides produce different colors.Pigments of copperthe reduction process. It also aids eventually in the separation of the molten copper from the slag once the melt has cooled down. Specifically, iron ore combines with the unwanted sand particles that just happen to be contained in the ore. The immense heat was accomplished by burning charcoal com￾bined with blowing air into the furnace either by mechanically ac￾tivated bellows and/or through blow tubes (called tuyères) (Figure 1.2), or by placing the furnace near the top of a mountain where the updraft winds were utilized. It is still a mystery today how Neolithic man could have found this chain of procedures without a certain degree of intuition or possibly the help of initiates. Archaeo-metallurgists have recently ruled out the hypothesis that copper could have been accidentally formed in campfires whose enclosures may have consisted of copper-ore–containing rocks. The temperatures in campfires (600–700°C) are known to be too low for smelting copper and the reducing atmosphere does not persist for a long enough time. (However, lead, which has a lower melting temperature, can be smelted this way from its ore.) It is believed today that the “technology” of copper smelting was probably borrowed from the art of making pottery, which was de￾veloped nine or ten thousand years ago or perhaps even earlier at certain locations. Indeed, the oldest known artifact made of baked clay is a fertility figurine called the “Venus of Vestonice,” which was found in the Czech Republic and supposedly dates back to about 23,000 B.C. (see Figure 15.1). In general, however, copper smelting and pottery seem to appear at comparable times in his￾tory. Specifically, Neolithic man had observed that mud bricks harden when dried in the sun and soften when again exposed to rain. A deliberate attempt to accelerate the drying process by ex￾posing the mud bricks to the heat of a fire probably led to the ob￾servation that an irreversible hardening process had occurred. A chemical transformation near 500°C causes a permanent consis￾tency of clay which makes it water-resistant. It can be reasonably assumed that this observation eventually led to the systematic de￾velopment of the art of pottery and the design of kilns instead of drying clay over or under an open fire. Neolithic man must have observed that stacking pots on top of wood fuel and covering this pile with fragments of pottery and earth would increase the tem￾perature. Eventually, kilns with permanent walls were developed, parts of which still exist today, dating back to the beginning of the sixth millennium B.C. We shall return to this subject in Chapter 15. Neolithic people have decorated some pottery utilizing proba￾bly the same ground-up metal ores (mixed with a lead oxide bind￾ing agent) that were used customarily for tribal body painting. Var￾ious metal oxides produce different colors. Pigments of copper 1 • The First Materials (Stone Age and Copper–Stone Age) 7