A piece of lead from Tel Dor, from about 2,500 years ago. The researchers created a graph that describes the relationship between the age of the lead and the amount of food products found on it. Photo: Photo Lab, Weizmann Institute
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The Lead Periods by Ran Shapira, Haaretz
The slow rate of consumption of lead made it a versatile metal thousands of years ago. In many archaeological excavations, tiles, pipes and weights made of lead were found. Lead was also used to coat ships, to prevent the adhesion of algae, shells and molluscs.
Lead that has undergone eating processes (corrosion) differs in its physical properties from lead that has not eaten. The differences are especially noticeable when the lead is in a state of superconductivity. Superconducting materials are endowed with two main properties - electricity flows through them without resistance and they repel a magnetic field from them.
To make lead a superconductor, it must be cooled to a temperature of 266 degrees Celsius below zero (7.2 degrees Kelvin). While the lead becomes a superconductor, the corrosion products accumulated on its surface remain in a normal state.
Prof. Shimon Reich from the Department of Materials and Surfaces at the Weizmann Institute developed a method for dating lead found in archaeological excavations, based on the difference between the magnetic behavior of lead at very low temperatures and the magnetic behavior of its byproducts.
Dr. Shariel Shalu, an archaeologist from the Department of Maritime Civilizations at the University of Haifa, who studies ancient materials at the Kimmel Center for Archaeological Sciences at the Weizmann Institute, assisted Prof. Reich in gathering information and provided him with lead from two archaeological sites - Tel Dor and Caesarea. Most of the objects used were lead plates, that were used as fishing weights in the Persian period (about 2,500 BC
year), in the Byzantine period and during the Crusaders. The arrows used by the researchers were well dated, depending on the layer and the site where they were found.
Together with Dr. Gregory Leitos, a metallurgist in the Department of Materials and Surfaces at the Weizmann Institute, Prof. Reich tested the magnetic properties of the lead objects. The tests were done at a temperature where lead is a superconductor, and thus information was obtained on the amount of uncorroded lead in each object. In the second step The objects were weighed at room temperature, to know their total mass - lead and food products together.
The difference between the mass of the object at normal temperature and the mass of the lead measured in the state of superconductivity is the mass of the digestion products in each object.
The researchers created a graph that describes the relationship between the age of the lead and the amount of food products found on it. In the future, archaeologists will be able to use this graph and the new method to determine the age of lead objects found in excavations.
Prof. Reich and Dr. Shalu say that the new method is the first to date metals and does not depend on organic findings. The only existing dating method, based on materials found in excavations and not on the hardness of time, place, technology, architecture, art, etc., is through the measurement of Carbon 14 isotope This isotope is formed in every organic body (plant or animal) and it fades from the day of death. The amount of the isotope remaining in the remains of the owner Life or plants allows you to determine how much time has passed since their death.
Dr. Shalo intends to test the compatibility between the two methods, by comparing lead parts with wooden parts found in ancient ships in Caesarea and Dor. The wood will be dated by carbon measurement, 14 the lead by the new method. A good match of the two dates will give additional support to the new method of dating artifacts lead.
Prof. Reich and his colleagues are now working on measuring additional lead samples, from different sources, in order to reduce the margin of error of the new method. At this point, the range of error in measurements using this method is about 200 years. The more lead samples there are, the smaller the margin of error will be.
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