Mössbauer and mineral magnetic studies on archaeological potteries from Adhichanallur, Tamilnadu, India

Abstract

Megalithic potteries collected from Adhichanallur, Tamilnadu, India (Lat. 8 • 44 N; Long. 77 • 42 E) have been subjected to various spectroscopic and rock magnetic studies. The type of clay, their origin, level of structural deformation due to firing, firing temperature and atmospheric condition followed during making the potteries are analyzed. The potteries were subjected to Mössbauer and X-ray diffraction studies to analyze the iron phases in them. It is found that the samples were made of local clay (red clay), fired above 600 • C under open atmospheric and/or reduced atmospheric conditions and air has been allowed during cooling. The Mössbauer spectra reveal the presence of Fe 3+ , Fe 2+ and iron oxides of hematite and magnetite. The firing temperature and firing conditions established from Mössbauer studies are similar to the observation made from FT-IR studies. The magnetic mineral types, the mass fractions and the domain states of the constituent magnetic grains were elucidated from a range of rock magnetic measurements including variation of susceptibility with low field, frequency and temperature, hysteresis parameters and isothermal remanence acquisition data. The magnetic mineralogy of most pottery samples was dominated by magnetite/(titano) magnetite, while magnetic grain size spectrum varies from very fine (super paramagnetic) to fine (stable single domain, pseudo single domain). The reversible thermo magnetic behavior reflects no mineralogical transformations during reheating and all the samples show same Curie temperature 580 • C due to magnetite. From the above information it is demonstrated that these samples are suitable for determining the reliable ancient geomagnetic field intensity values existed during that period. R. Venkatachalapathy (B) C.A.S in Marine

X-ray Diffraction Analysis of Clay Particles in Ancient Baekje Black Pottery: Indicator of the Firing Parameters

“…Based on these results, PN1 and PN2-in which magnetite was detected in the blackened parts-were classified as RB-type pottery, and PN3, in which only hematite was detected, was classified as BP-type pottery, fired in an oxidizing environment. The iron oxide composition for each type of black pottery is consistent with the Mössbauer spectroscopy results of black pottery from the same site [36], and with the properties of the RB pottery reported from various cultural spheres [12][13][14][15][16][17][18][19][20][21][66][67][68][69]. This finding implies that, in the ancient Baekje period, not only were the BP and BS types produced, as reported previously [27,28,[30][31][32][33][34][35], but the RB type was also produced.…”

“…However, in the case of the diffraction patterns of the bulk powder, the peaks of mica are difficult to analyze, as they are present in small amounts due to the higher diffraction intensity of quartz and feldspar. Furthermore, even though the detected minerals were known as white or clear colors, iron oxides-mineralogical factors that induce brownish or blackish colors-were not detected among the soil component materials [6][7][8][9][12][13][14][15][16][17][18][19][20][21][50][51][52]. In particular, the iron oxides in the soil exist as nano-sized particles that cover individual soil particles and have low crystallinity-they are almost amorphous in nature [53][54][55][56][57][58][59].…”

“…According to the blackened trend (Figure 2), clay mineral composition (Figure 4), and iron oxide composition (Figure 5) observed in the studied ancient Baekje black pottery, the firing technique applied while manufacturing each fragment can be estimated, as shown below [12][13][14][15][16][17][18][19][20][21]36,52,[64][65][66][67][68][69][70][71][72][73][74][75]:…”

“…In addition to its artistic and archeological value, this type of pottery is important evidence that ancient people used scientific techniques to materialize the black color. Black pottery is classified into the following three types based on the production techniques and materials used for color development: the black smoked (BS) type, which is produced by a firing technique that allows carbon-based black material, such as soot, to deposit on the surface and penetrate the interiors [1][2][3][4]; the black painted (BP) type, in which a carbon, Mn oxide, or reduced iron-based black material is directly painted, with an adhesive, onto the surface of the pottery [5][6][7][8][9][10][11]; the reduced black (RB) type, in which the color development takes place due to an increase in the percentage of Fe 2+ and magnetite converted from iron oxides in the raw material soil, through reduction firing [12][13][14][15][16][17][18][19][20][21]. The specific classification of pottery into the above three types requires precise identification of the minerals used for color development and their chemical compositions.…”

Applications of FTIR and57Fe Mössbauer Techniques in Studies of Recently Excavated Indian Archaeological Pottery

“…According to Ramaswamy et al [29] and Venkatachalapathy et al [30], the presence of higher percentage of Fe 2+ reveals the reduced atmosphere and is the reason for black colour of the pottery, whereas higher percentage of Fe 3+ is due to the strong oxidizing atmosphere which reects reddish colour of the pottery. The authors have also reported that the magnetic hyperne eld value of 508510 kOe is attributed to the presence of hematite.…”