Determination of origin of Ancient Marble Sculptures and Monuments
Why investigates the origin of the ancient monuments of marble?
– This stuidy was conducted by Dr. Kiki Polikreti, Physicist
To investigate the origin of the marble sculptures and monuments, gives information on the relationship between people (religious or economic nature ties, relations of subordination, etc.) on trade and maritime or land transport routes, exchange raw materials and know-how (Herz and Doumas, 1991). The exploitation of marble quarries constituted since ancient times, important economic parameter vector and technological development and robust trade. Where art in particular, identification of the origin enlightens the archaeological fundamental question of what ultimately was transported from place to place, the raw materials, the artists or the aesthetics?
During Restoration procedures, identification of the origin gives indirect information on the physico-chemical properties of marble, which are necessary for the design of maintenance steps. If excluding the maintenance or restoration is restoration of the monument, the indication of the quarry of origin is necessary so that the parts are missing or need to be replaced, supplemented by pieces from the same rock. Often welding broken during the restoration has been proven wrong as the origin proved different for the various pieces (Herz and Wenner 1978).
Knowing the origin of the marble is also an indirect way though not exact dating, since the tapping of the main quarries least did not start at the same time. It should be noted that the investigation of the origin brought to the fore the study of ancient quarries, quarrying techniques, the organization of the exploitation and transportation of marble tumors. It was revealed in this way a multitude of forgotten monuments that can give a huge amount of information in the field of archaeology now called industrial (Pensabene 1992).
Ancient marble quarries
The marble sculpture in Greece first appeared at the end of the Mesolithic era (5000 BC). The famous Cycladic figurines (the Bronze Age, 3rd millennium BC) are the representation of human figures carved on pebbles already shaped by the action of the sea. The first marble sculptures displayed in Naxos (7th c. BC) (Kokkorou – Alevra 1992, Kokkorou – Alewras 1995). The extensive use of marble from then until now in Greece should be attributed, among others, in the abundance of rock in the Greek subsoil.
Organised quarrying expressed initially with the technique of cutting of parallel-piped volumes with an original etching grooves. This technique is attributed to the Egyptians (2600 BC), of which transferred to the Minoans and the Mycenaeans of them (Waelkens et al. 1988). The oldest quarry in Greece with traces of quarrying is organized Melanes Naxos and its operation goes back to the 7th century BC (Kokkorou – Alevra 1992).
The distinction of the ancient quarries of the newest is not easy if the newer operation usually starts at the points of the ancient quarry. Ancient sectional surfaces have openings for positioning wedges or characteristic continuous streaks treatment with tyko or needle. The list of known ancient quarries is large and added daily and new data (Manda 1993). Times are given in Table 1 holding several ancient quarries.
Methodology and problems of determining origins
To allow the determination of origin of a marble monument theoretically required large number of samples from all ancient quarries and an appropriate technical analysis. The results of the analyzes are the database with which it is compared to a sample of unknown origin with the help of statistical methods to identify unparalleled and so the area of origin.
Extensive and accurate sampling is one of the most important stages of the above procedure. The large number of samples is not enough. They should be selected so as to cover all potential geological quarry while avoiding samples from individual veins growing dispersion parameters without representative.
The choice of the technique is also important as it has been shown that a single technique is not effective and often two or more. If the technique allows many parameters, choosing those that give optimal separation and processing them in order to highlight the distinction is the subject of statistics. The statistical techniques of classification, clustering analysis and principal eigen vectors are put at the service of archaeometry to solving problems of origin since the early 1960s.
Finally it should be noted that because of sampling failure of all possible ancient quarries and techniques to separate quarries together, the general question “What is the origin of the marble this artwork?” not easy to answer. Questions that limit the number of possible places of origin in two or three, based on historical information are easier to answer.
Techniques for determining origin
In petrographic microscope detected secondary minerals, characterized tissue and texture of marble, the address stochastic detected if present, measure the size of crystals and other mineralogical characteristics specified by the parent sedimentary rock, but mainly from the process of transformation (Blackburn and Dennen 1990). The sample studied in thin section form (0,02-0,03mm) magnification and passing natural or polarized light.
For the first time in 1890 Lepsius studied a collection of 409 samples of marble from archaeological findings and resulted in some 12 types of marble with specific characteristics such as the size of the crystals, texture, tissue, visible impurities etc. (Moltesen 1994). These simple variations used by archaeologists to date. Figure 1 gives a diagram with the most important ancient quarry grain sizes.
A drawback of the technique is the relatively large size of the sample is required, which makes it difficult to apply in investigating origin archaeological findings.
Identifying stable isotopes
To determine the origin of marbles isotopes mainly used 12C, 13C, and 16O, 18O. The ratio of these isotopes in marble depends on the parent sedimentary rock, mainly from the isotopic composition of the fluid phase involved in the process of transformation.
The sample (5mg) passes through the mass spectrometer, dissolved in H3PO4 (100%). The results are given in chiliostiaies differentials ratios 13C / 12C and 16O / 18O of the sample from the grounds of the reference substance PDB (fossil Pee Dee Belemnite).
The method was originally (Craig and Craig 1972) promising since the number of samples quarries separated completely. By increasing the number of quarries, however, large areas of the coating created in many cases make an accurate determination of origin impossible (Herz 1985, 1987, 1992).
Analysis by Neutron Activation
Analysis by Neutron Activation identifies a series of concentrations of trace elements characteristics of the genesis conditions of the rock. During the experimental procedure, marble dust (50-500mg) is subject to irradiation with thermal neutrons in a nuclear reactor. The cores of certain isotopes capture a neutron and become radioactive Spyropyran emitting gamma radiation. The energy of the radiation is characteristic for each isotope and the number of photons c is proportional to the content of the element in the material.
Since 1965 (Rybach and Nissen) method was used widely (Moens 1988, Grimanis and Vassilaki – Grimani 1988, Manda 1993) for determining origin marbles. The concentrations of most trace elements but vary greatly in the same quarry, so the data for the various quarries to overlap. So Neutron Activation is effective in the determination of origin when the quarries are examined in pairs and each time choose the most appropriate data from the data set analyzed (Manda 1993).
Cathodoluminescence (CL) Analysis
Cathodoluminescence (CL) is the emission of visible light after bombardment of the material by electrons. The sample is analyzed in the form of thin section so it can be considered micro-topographic distribution Cathodoluminescence. The results of the analyzes are given in the form of photographs, color charts and emission spectra.
The overall color picture of the material varies in some quarries hence the Cathodoluminescence used as an additional method of origin in areas covering the results of isotopic analysis (Barbin et al. 1989, 1992, Blanc 1996).
Breakdown Spectroscopy Electron Paramagnetic Resonance (EPR)
Spectroscopy EPR, in Calcite marbles and detects ions Mn2 +, Fe3 +, inorganic and organic free radicals and crystal defects. The sample in the form of powder (50-200mg) is placed in a changing magnetic field, while simultaneously receives fixed frequency microwave irradiation. During scanning, the magnetic field takes values which equalize the spacing between the energy levels of microwave energy. Paramagnetic centers absorb microwave energy and are excited to a higher energy level (Pilbrow 1990).