The Turin Shroud (TS), the most important Christ’s relic, is a well known object in which a body image is imprinted. Numerous scientific approaches were realized concerning this precious relic (Marion & Lucotte, 2006) . We have obtained a small triangular sticky tape that was sample d on its surface (corresponding to the Face of this body) and we concentrated in the past years on the study of microscopic organic structures located on the surface of this sticky tape, including: linen fibers (Lucotte, 2015a) , pollens and spores (Lucotte, 2015b) , red blood cells (Lucotte, 2015c) , skin debris (Lucotte, 2016) , an hair fragment (Lucotte & Thomasset, 2017a) and osseous remains (Lucotte & Thomasset, 2017b) . More recently, we published gold and silver particles (Lucotte, 2022a) , and lapis lazuli particles (Lucotte & Thomasset, 2023) , detected on the surface of the triangle.

In a preliminary analysis (Lucotte, 2012) , we studied some particles, notably the b8 and the ei4 particles, that seems to look like (by their morphologies and sizes) to red blood cells; they are in fact some peculiar clays (Lucotte, 2022b) , with elevated values of iron oxide in their compositions, that conferring to it the red colour observed in optical microscopy.

In the present study, for obtaining precisions about these peculiar red clays, we observe and characterize in details the clay particles (including b8 and i4) located on the surface of the triangle, presenting such similar peculiarities. A total number of fifteen particles were so detected.

The material is a small (1.36 mm height, 614 µm wide) sticky tape triangle at the surface of which all particles were deposited. For practical reasons, the surface of this triangle was subdivided in 19 (named A to S) sub-samples areas (Lucotte, 2017) . The positions of each particle sticking to the triangle surface were located in a double system of coordinates (in 186 adjacent squares of 50 × 50 µm). Particles of the sample were observed, with any preparation, on the adherent part of the triangle surface. All the particles described here were studied by optical microscopy and by SEM (Scanning Electron Microscopy)-EDX (Energy Dispersive X-ray) analysis.

Most of the particles studied were first observed by optical microscopy using a photo-microscope Zeiss, model III, 1972. The corresponding photographs were named as direct when they correspond to those studied by SEM-EDX, and as inverse hen it is the other side of the triangle that was observed.

Two SEM apparatus (SEM1 and SEM2) were used; both are Environmental versions: 1/A Philips XL. 30 instrument. GSE (Gaseous Secondary Electrons) and BSE (Back Scattered Electrons) procedures were used, the last one permitting the detection of heavy elements. 2/A FEI model Quanta 25 of FEG, both in LFD (Large Field Detector) and CBS (Circular Back Scattering) procedures.

Elemental analysis for each particle were realized by EDX, the SEM1 apparatus being equipped with a Bruker probe AXS-EDX and the SEM2 apparatus with a probe model X-flash 6/30. Each elemental analysis is given in the form of a spectrum, with kiloelectrons/Volts (ke/V) on the abscissa and elemental peak heights in ordinates. Highly resolutive (HR) spectra are those where the ordinate scale is in logarithms, for a better distinction of little peaks.

Normal compositions in elements are those where carbon and oxygen are not taken in consideration.

The enlarged (about 1200×) optical view of Figure 1 shows the right part of the B area of the triangle. Three red particles are visible in this view: the b8 particle and the b 24 and b25 (red-brown) particles. Adjacent particles b24 and b25 are located to the left part of b22, which is a golden particle (Lucotte, 2015a) .

The SEM1 photograph of Figure 2 shows the b8 particle. It is a rounded particle of a maximal diameter of about 12 µm. Because of its form and colour, it mimics red blood cells (Lucotte, 2015c) . There are three deposits at the b8 surface: a triangular Diatom, and two micro-filaments of titanium (Ti). The b8 surface is not smooth, and shows some evidence of micro-heterogeneity.

The b8 spectrum shows that it is a typical clay: the silicium (Si), the aluminium (Al) and the magnesium (Mg) peaks are in order of decreasing heights; there is potassium (K) and calcium (Ca). It is an iron-rich clay, because the iron (Fe) value is of about 41% and there are traces of manganese (Mn), attesting the “mineral” nature of the iron. There are little peaks of sodium (Na), of sulphur (S) and of chlorine (Cl) and also some traces of phosphorous (P).

The SEM1 photograph of Figure 3 shows the b24 particle, which is with hexagonal outlines and has a maximal measurement of about 6 µm. It is a clay, with an important main peak of iron; it has phosphorous and sulphur traces. This particle is contaminated by the gold (Au) of the b22 particle.

Similarly the b25 particle is also with hexagonal outlines, with a maximal measurement of 6.5 µm. It is also a clay, with an important mean peak of iron and little phosphorous and sulphur peaks.

Because of the proximity of b23 and b26 particles with the right border of the B area, we cannot see their colours in optical microscopy. They are two particles with hexagonal outlines, and with maximal sizes of 6 µm and 5.5 µm, respectively.

The b23 spectrum (Figure 4) is that of a clay with an elevated mean peak of iron, and phosphorous and sulphur traces. This particle is contaminated by the gold of b22. The b26 spectrum is also that of a clay with an elevated main peak of iron, and little peaks of phosphorous and sulphur.

Because of the proximity of a25 and a27 particles with the right border of the A area (Figure 5), we cannot see their colours. The a25 particle is with pentagonal outlines and of 6.5 µm of size; its spectrum is that of a clay with an important mean peak of iron, and with phosphorous and sulphur traces. The a27 particle is a little (3 µm) rounded particle; its spectrum is also that of an illite, with an important mean peak of iron and with phosphorous and sulphur little peaks (it is contaminated by titanium).

The optical photograph of Figure 6 of the lower part of the A area shows that the a41 particle is of a red-brown colour. It is a pentagonal particle of 5.5 µm of size; its spectrum is that of a clay with an elevated mean peak of iron. It has an important peak of phosphorous and a little peak of sulphur.

The SEM2 photograph of Figure 7 shows, in the right part of the G area, the g27, g30 and g33 particles; g27 is in fact (see the SEM photograph of Figure 8) a complex particle, constituted of at least seven parts (1 - 7). Its maximal length is of about 18 µm. The g30 particle is of small size (about 3.5 µm) and with a triangular form, but careful examination (see Figure 8) shows that it is driven under part 6 of g 27, and so must be of greater size. The g33 particle is squared in form, with a maximal size of 10.5 µm. These three particles are covered by very fine deposits of calcium carbonate micro-grains.

The inverted optical view of Figure 7 shows that the g27, g30 and g33 particles are of red-brown colours.

Figure 8 shows the g27 spectrum, that is of a clay with an elevated mean peak of iron; it has little peaks of phosphorous and sulphur. This spectrum shows an elevated value of the main calcium peak.

Figure 9 shows the spectra of the g30 and g33 particles. Both are those of a clay with important main peaks of iron. The two spectra have peaks of phosphorous and sulphur, and elevated values of the main calcium peaks.

The inverted optical view of Figure 10 shows, in the right part of the I area, the red-brown colour of the i4 particle. The SEM1 photograph of Figure 10 shows that it is an elongated particle, with at least 9.5 µm of size. Careful examination of its surface permits to see that it is entirely constituted of some forms of micro-organisms of characteristic patterns.

The i4 spectrum is that of a clay, with an important peak of iron; it has little peaks of phosphorous and sulphur. It shows an elevated value of the main calcium peak, and traces of copper (Cu).

The SEM1 photograph of Figure 11, of a left part of the J area, shows the j50 and j51 particles. The j50 particle, detached from j51, is a little (1.5 µm) squared particle. Its spectrum is that of a clay, with an iron content of about 60%. It has a little peak of phosphorous. The j51 particle is elongated, with 7.5 µm of maximal length. There is also some evidence of micro-organisms on its surface. Its spectrum is that of a clay, with an elevated value of the main peak of iron; it has a little peak of phosphorous.

Because of the proximity of j50 and j51 particles with left border of the J area, it is difficult to see their colours. Careful examinations of some optical views of the region shows however one yellow-red spot corresponding to the j50 particle, and a pale-red spot corresponding to the j51 particle.

The inverted optical photograph of Figure 12 shows, in the central part of the L area, the red colour of the l11 particle. The SEM photograph of that figure shows that l11 is an elongated complex particle, of a maximal length of 9 µm, constituted of at least three parts (1, 2 and 3). There is also evidence of micro-organisms on its surface.

The l11 spectrum is that of a clay, with an iron value of about 56%. It has a great peak of phosphorous (of value of about 5%) and a smaller peak of sulphur (of a value of about 2%); the value of chlorine (about 6%) is also relatively elevated.

Table 1 lists and characterizes the fifteen (three in the A area: a25, a27 and a41; five in the B area: b8, b23, b23 and b24, b25 and b26; three in the G area: g27, g30 and g33; one in the I area: i4; two in the J area: j50 and j51; one in the L area: l11) iron-rich clay particles detected in the various areas of the triangle. All have

spectra of typical clays, with elevated iron-values; the iron oxide conferring a red colour, all these (when observable in optical microscopy) particles are of red-brown or red colour. So these iron-rich clays participate, together with those of hematite, biotite and cinnabar already detected (Lucotte et al., 2016) , to the observed reddish tint of the triangle (Lucotte, 2017) .

These iron-rich clays are of some interest for understanding the origin of the TS, because the soil of Mt. Sion (in Jerusalem) contains some red illites with quasi-similar spectra (Fanti et al., 2015) . However more accurate analyses are necessary for a complete identification of these minerals, which are very similar to the clays of other Mediterranean areas influences by the winds of the Sahara desert.

The forms of these particles can be rounded (a27 and b8) or more elongated (i4, j51 and l11), but most often with angular outlines. The most elementary form is that of pentagonal or hexagonal particles (a25, a27, a41, b23, b24 and b25). Two particles (g33 and j50) are squared, and one (g30) is triangular.

Table 2 summarizes the multipartism of particles, and their phosphorous and sulphur contents. There is heterogeneity in the surface of the b8 particle. Particle g27 is in seven parts. Visible micro-organisms are observed on the surfaces of the i4, j51 and l11 particles. The i4 surface (Figure 10) appears as quasi-entirely make-up of these micro-organisms, and similar patterns are observed for j51 and l11.

All the particle spectra (but j50) have sulphur little peaks, reaching 1% in b8 and 2% in l11. All these particles have phosphorous in their spectra, most often in the form of traces (a25, b8, b23 and b24) or little peaks of this element (a27, b25, b26, g27, g30, g33, i4, j50 and j51), reaching 5% in l11.

We detected fifteen clay particles (a25, a27, a41; b8, b23, b24, b25, b26; g27, g30, g33; i4; j50, j51 and l11) on the various parts of the triangle surface. They have the following characteristics: they are particles of maximal sizes comprised between 1.5 µm (for j50) and 19 µm (for g27). Their forms are rounded or more elongated, but more often with angular outlines.

They are alumina-silicate clays, with an elevated content (up to 56% of the normal composition for particle l11) of iron; when observable, their colours are red or red-brown. Interest of these particles concerns their potential relationships to blood.

All these particles have a little quantity of the phosphorous element in their compositions (up to 5% for the particle l11). The biggest ones show some heterogeneity at their surfaces; visible micro-organisms, constitutive of these clays, are observed on the surfaces of particles i4, j51 and l11.

The authors declare no conflicts of interest regarding the publication of this paper.

Lucotte, G., Thomasset, T., & Deroin, T. (2024). Iron-Rich Red Clays on the Turin Shroud: Optical Microscopy Studies and SEM-EDX Analyses. Archaeological Discovery, 12, 66-81. https://doi.org/10.4236/ad.2024.121004