As copper-containing objects age in a slightly corrosive environment, without contact with soils or sea air, a layer of tenorite (Cu O) continuously forms over the primary cuprite patina.This occurs because cuprite reacts with oxygen from the air to preferentially form tenorite in an atmosphere containing CO2 or in the presence of calcareous materials.Presented in the journal Angewandte Chemie, their electroanalytical method is based on the voltammetry of microparticles.
Quite convincing dates are sometimes arrived at by importing parallels from other contemporaneous cultures.
This parallelism is formed due to trade relations, particularly wehen trade followed in both directions.
Antiquities and potteries of Roman origin were found in association with the finds of Indian origin.
With the aid of these dated imports it was possible to date the associated Indian objects to the first two centuries A. Similarly NBP and PGW has helped in fixing the chronology of numerous sites. Sometimes dates are also obtained with the assistance of astronomy.
In such cases subjective element cannot be ruled out.
But, for a single culture site the method is quite reliable.
It shows a steady increase with increasing corrosion time, as demonstrated with a series of antique coins from various collections, including the Prehistory Museums of València and Xàtiva (Spain), as well as the artificial ageing of Euro cent coins made of copper.
The researchers were able to use the coins to establish a calibration curve that can be used to date objects of unknown age.
Basing on this principle, the cultural assemblages found in different layers can be assigned a chronological personality. In practice it is found that the mounds are disturbed9 by all sorts of pits and dumps.
For example, if the cultural contents of the lower deposit are Mauryan in character, appropriately this deposit may be assigned a date between 400-200 B. Similarly, if the cultural equipment of the upper deposit are of the Sunga period, this deposit has to placed between 200-73 B. Quite often, the archaeologist decided the change of stratum on the basis of the feed of the deposit.
Even when the absolute dates are available, we have to supplement the information with relative dating.