SYNCHROTRON RADIATION AND...

SYNCHROTRON RADIATION SYNCHROTRON RADIATION SYNCHROTRON RADIATION AND ARCHAEOMETRYAND ARCHAEOMETRYAND ARCHAEOMETRY

Simona Quartieri Dipartimento di Scienze della Terra

Università di Messina

In general, the studies of ancient objects of archaeological or artistic interest have undergone significant improvements in the recent years under

the impulse of new non- or micro-destructive methods for analyzing materials, such as:

� micro-beam techniques� portable instruments� synchrotron radiation

There are many reasons for usingsynchrotron radiation in archaeometry:

i) X-ray beams with high intensity and low divergence, as produced at synchrotron radiation facilities, are highly suitable tools for examining fragile, valuableand/or unique artefacts with minimal or no damage.

ii) We can achieve information about major- and trace-level composition of the objects, about the chemicalstate of one or more atomic species and/or aboutcrystallographic phases, that are present in the materials even in very small concentrations.

iii) Since the materials and objects encountered in the field of art-analysis, archaeology and conservation are often complex in shape, covered with alterationlayers and/or may be highly heterogeneous, the use of X-ray micromicro beamsbeams is often mandatory to allow forthe measurement of local rather than bulk properties.

The questions that archaeologists ask more often regarding an object are:

� what material is it made of (composition)

� when was it made (dating)

� where was it made (provenance)

� how was it made (art technology)

� how can we avoid its destruction (conservation)

InformationInformation fromfrom SRSR--techniquestechniques��Elemental microanalysis down to the subElemental microanalysis down to the sub--ppmppm level is level is possible by means ofpossible by means of ��--XRF XRF (X(X--ray fluorescence analysis). ray fluorescence analysis).

��Local structural and chemical state determinations of Local structural and chemical state determinations of selected (trace) constituents are possible by applyingselected (trace) constituents are possible by applying XAFS XAFS and and ��--XAFSXAFS (X(X--ray absorption spectroscopy) ray absorption spectroscopy)

��Information on the presence and nature of crystalline Information on the presence and nature of crystalline phases can be obtained viaphases can be obtained via XRDXRD (X(X--ray diffraction), ray diffraction), which which usually employ Xusually employ X--ray photons with energies in the 0.5 to 30 ray photons with energies in the 0.5 to 30 keVkeV range. range.

��Entire objects may be bathed in highlyEntire objects may be bathed in highly--energetic energetic synchrotron beams to allow high qualitysynchrotron beams to allow high quality radiographicradiographic orortomographictomographic imagingimaging measurements, revealing the internal measurements, revealing the internal structure of these structure of these artefactsartefacts..

Powder diffraction is a very widely applied technique in the geological and material sciences, even with conventional sources. When it is supported by the use of SR, it can provide excellent signal/noise ratios and strong peak resolution. Moreover, SR allows performing micro-diffractometric investigations.

The analysis of cosmetic samples is delicate since they are often heterogeneous at micron scale and may be composed of a mixture of organic and inorganic phases.

Their study requires non-destructive techniques, with high detectivity, high lateral resolution, and high chemical sensitivity (atomic, molecular and structural probes).

Manufacturing cosmetics in ancient EgyptManufacturing cosmetics in ancient EgyptStudy of cosmetic powders from ancient Egypt, dating from 2000 to 1200 BC, that were preserved in their original containers

Manufacturing Manufacturing cosmeticscosmetics in in ancientancient EgyptEgypt

Laurionite and phosgenite are very rare in nature and could not have been extracted from the mines in sufficient quantities for the preparation of the cosmetics

Intentionally manufactured by artificial synthesis !

Laurionite (PbOHCl) and phosgenite (Pb2CO3Cl2) could in principle had been formed for alteration of the basic components by chloride, but no foreign cationsor chlorinated phases were detected in the more than 50 analyzed samples. Therefore the alteration of natural lead minerals within the make-up is unlikely.

The synthetic or natural origin of a product can be distinguished by the analysis of the

diffraction peak profiles

The synthetic origin of PbOHCl e Pb2Cl2CO3 has been confirmed by the analysis of the diffraction peak profiles, comparing the effects due to the strains and to the crystallite dimensions with those present in the natural phases.

RESULTS:1- galena present in the cosmetics was crashed, probably to confer the make-up the desired texture and brightness2- the peak profiles of laurionite and phosgenitedo not exhibit strain effects, suggesting that the crystallites were produced by direct synthesis.

XRD LINE PROFILE ANALYSISXRD LINE PROFILE ANALYSIS

Why to produce white components to be added togalena when cerrusite was available?

In the ancient Egypt, cosmetics were not only used for aesthetic purposes, but also for their therapeutic, hygienic and magic properties. The Greco-Roman texts mention that the white precipitates synthesized by PbO were good for eye and skin care. These lead compounds could be used as bactericides and as a protection for the eye against exposure to the sun’s rays.

Marine Cotte, ID21, ESRF

The advantages of classical IR spectroscopy (non destructive, simultaneous information on both organic and mineral phases and on both composition and structure) are enhanced by the use of SR brightness (high lateral resolution with high signal-to-noise ratio).

20062006

The organic phase is composed of lead soaps, among which lead palmitate, and is located in the core of the particles.

In contrast, phosgenite (Pb2CO3Cl2) is detected mainly near the surface, which suggests that it was added at the end of the preparation, probably to keep it intact and more accessible for a possible therapeutic action.

Conclusions

MAYA BLUEMAYA BLUE PIGMENTPIGMENT

G.G. Chiari, R. Chiari, R. GiustettoGiustetto, G. , G. RicchiardiRicchiardi (2003) (2003)

EurEur. J. . J. MineralMineral.. 15:2115:21--3333

G.G. Chiari (2005) Chiari (2005) IUCrIUCr, Firenze, Firenze

In Mexico it was used until the end of ‘600. In Cuba it is found on walls dating 1830. It was “re-discovered” in 1849, together with the remains of the Maya civilisation.

Maya BlueMaya Blue is a synthetic pigment, produced by the Mayas probably around the VIII century AD

A bright turquoise, it was used in mural paintings, statues, ceramics, codices, and even to tint prisoners to be sacrificed.

Maya BlueMaya Blue is extremely stable: it can resist the attack of boiling, concentrated nitric acid, alkali and any sort of organic solvents.

Its composition and structure was a mystery for a long time. Kleber (1967) proposed a mixture of the colourless clay palygorskite and the blue organic dye indigo:

he was righthe was right

PALYGORSKITE PALYGORSKITE [(Mg, Al)4 (Si)8 (O, OH, H2O)24 nH2O]

Micro-channels filled with weakly bound zeolitic H2OThe cations complete their coordination with tightly bound structural H2O

Fibrous clay (from few to some tens of �)

Indigo is one of the most common organic dye, known even in the ancient Egypt, India and China and largely used also by Romans. The Majasextracted it from the leaves of Indigoferasuffruticosa, a native plant of Mexico.

Several hypotheses were proposed on how Maya Blue was produced using only the crude technology at the Mayas disposal

Palygorskite projected on (001)

Following one of these hypothesis, upon heating around 100° C, indigo would enter the palygorskite channels expelling the weakly bonded water molecules and forming strong chemical bonding interactions with the clay structure, so giving rise to the pigment Maya Blue.

Maja Blue pigment ?

SR X-ray powder diffraction at GILDA beamline

The powder patterns of paligorskite and of the clay-dye complex were very similar, due to the very low amount of dye which interact with the clay mineral, hence SR-XRPD was applied to obtain a better peak-to-background ratio and a better angular resolution.

Electron Density map at the level of indigo

Indigo

MODEL OF ENCAPSULATION OF INDIGO IN THE PALYGORSKITE FRAMEWORK

This configuration is extremely unlikely from the energetic point of view and, moreover, it is invalidated by two simple considerations:

Indigo can enter palygorskite channels only if the zeolitic water is removed (130 < T < 220°C).

HoweverHowever,, MAYA BLUEMAYA BLUE forms at about T=100°C !!

Even if indigo could displace water, the molecule has to break strong H bonds (� 1.8 Å between

indigo -C=O and structural water) to move inside the channels.

The formation of The formation of MAYA BLUEMAYA BLUE depends upon a depends upon a series of highly unlikely eventsseries of highly unlikely events.

ThermalThermal AnalysisAnalysis of of paligorskitepaligorskite (black) (black) and Maya Blue (and Maya Blue (redred))

The water loss at 120<T<300°C (ZEOLITIC ZEOLITIC water) is the sameis the same for both palygorskite and Maya Blue:

the two substances contain the same amount of water

A new theory is needed:A new theory is needed:

Indigo does not enter the channels but only Indigo does not enter the channels but only fills the grooves all around the crystalfills the grooves all around the crystal

Indigo

Indigo molecules are imbedded into the grooves.

Water does not have access to the groove because the hydrophobic part of indigo repels it.

Nitric acid cannot attack the indigo double bond because of steric hindrance.

Archaeometric applications of X-ray Absorption Spectroscopy

XAFS spectroscopy is a potentially very usefultechnique to be applied in archaeological studies.

�It is a non-destructive method which can be applied in air

�it virtually does not require any restriction on the type and size of the sample (metal, ceramic, glass, cloth, paper, etc.)

�it is applicable to most of the elements of interest, even in very low concentration.

All these characteristics are particularly important in archaeological applications, in which samples are precious cultural heritage made of very differentmaterials.

The The originorigin of color of color in in ancientancient glassglass

Various colors in glass can be causedby metal ions in them.

They are usually transition elementswhich absorb characteristicfrequencies of visible region.

This mechanism is also influenced bythe oxidation state of the metal cation.

Since the characterization of colorant and decolorant componentsis important in understanding the

manufacturing technique, XAFS has been applied to the study of the oxidation state of transition metals

in a number of glass samplescharacterized by different color

Application of X-ray Absorption Spectroscopy with synchrotron radiation to the study of glasses of archaeological interest

(Quartieri et al. Eur. J. Mineral. 2002)

Synchrotron X-ray absorption spectroscopy has been applied to the study of the oxidation state of iron and manganese in a number of glass samples of the 2nd century AD, characterized by different color (from pale green to pale brown) found in the Roman villa of Patti, near Messina.

-to test the influence of iron oxidationstate on the color of the studied samples

- to identify the possible decolorant roleof manganese oxide in the almostuncolored samples

Fe and Mn K-edge absorption spectroscopy experiments were focused to XANES and pre-edge regions, being these particularly sensitive to both coordination and oxidation state of the absorbing atom.

The spectra were collected directly on the glass fragments in the fluorescence mode on the GILDA-CRG beamline (ESRF).

SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2O K2O NiO Cu2O CoO Cr2O3 ClA 70.70 0.10 3.31 0.40 0.02 0.63 8.02 16.45 0.59 0.02 0.06 0.02 — 0.99B 65.89 0.18 3.39 1.00 1.20 1.11 8.98 14.31 1.15 0.06 0.03 — 0.02 0.91

C 65.51 0.20 2.83 0.97 1.40 1.24 8.72 17.45 0.69 — 0.06 0.02 0.01 0.88

ExperimentalChemical analyses of the glass samples.

Glass A: green; glass B: uncolored; glass C: pale brown.A

Fe K-edge

7100 7125 7150 7175

Energy (eV)

Olivine

Hematite

Magnetite

Glass A

7112.4 7113.9

7114.6