Ancient objects, dating

The use of the various tempera and of wax has been identified on objects dating back to ancient Egypt. The Eayum mummy portraits are beautiful examples of encaustic painting, ie, using molten wax as medium. A rather special variation was the technique used by the Romans for wall paintings. In these, the medium, referred to by Pliny as Punic wax, probably consisted of partially saponified wax. In Europe, wax ceased to be used by the ninth century. 

FIGURE 38 Lead coffin. Lead coffin (first—third centuries c.E.) from Jerusalem, Israel. Lead, widely used in many ancient civilizations, was one of the first metals to be recovered from its ores. Lead objects date back from as early as the seventh century b.c.e. In Mesopotamia molten lead was used to fasten bolts and shafts into masonry. In Syria it was made into rods used as currency, and in Greece it was cast into coins. During the Roman Empire the use of lead become so widespread that the health hazards caused by lead exposure are suspected to have been one of the factors affecting the fall of the Roman Empire. Since it is very resistant to corrosion, lead was also used by the Romans, for making coffins as the one illustrated. 

Method of dating ancient objects by determining the ratio of amounts of mother and daughter nuclides present in an object and relating the ratio to the object s age via half-life calculations. 

Gold objects dating to 2600 bce have been found. They were discovered in the royal tombs of the ancient civilization of Ur, located in the modem country of Iraq. These objects showed that humans had already learned how to work with gold this early in history. Some of the gold, for example, had been formed into wires. 

Silver also occurs as a free metal, but much less often than gold or copper. At some point, humans learned to extract silver from its ores. But that discovery must have occurred very early on in human history. Archaeologists (scientists who study ancient civilizations) have found silver objects dating to about 3400 bce in Egypt. Drawings on some of the oldest pyramids show men working with metal, probably extracting silver from its ores. 

The alkali metals are not found free in nature, because they are so easily oxidized. They are most economically produced by electrolysis of their molten salts. Sodium (2.6% abundance by mass) and potassium (2.4% abundance) are very common in the earth s crust. The other lA metals are quite rare. Francium consists only of short-lived radioactive isotopes formed by alpha-particle emission from actinium (Section 26-4). Both potassium and cesium also have natural radioisotopes. Potassium-40 is important in the potassium-argon radioactive decay method of dating ancient objects (Section 26-12). The properties of the alkali metals vary regularly as the group is descended (Table 23-1). 

The Nature and Discovery of Radioactivity Radioactivity is a fundamental part of the behavior of some atoms, and it also has many applications. For example, radioactivity is used to diagnose and treat diseases, including cancer, tii5uroid diseases, abnormal kidney and bladder function, and heart disease. Natural radioactivity is part of our environment and can be used to date ancient objects. The discovery of radioactivity led to the discovery of fission, which in turn led to the development of nuclear bombs and nuclear energy. 

Carbon Dioxide and Climate Change 70 Many Forms of Carbon 98 Energy-Saving Fluorescent Bulbs 117 Radon in Our Homes 140 Dating Ancient Objects 150 Nuclear Power Plants 158 Pheromones in Insect Communication 381 Vanilla 410 Plastics 483... 

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