synchrotron radiation and archaeometry · radiation to the study of glasses of archaeological...

SynchrotronSynchrotronSynchrotron RadiationRadiationRadiation andandandARCHAEOMETRYARCHAEOMETRYARCHAEOMETRY

Simona Quartieri Dipartimento di Scienze della Terra

Università di Messina

Quartieri - SILS 2006 Napoli

SynchrotronSynchrotronSynchrotron radiationradiationradiation and and and archaeometryarchaeometryarchaeometryHighly intense X-ray beams as produced at synchrotronradiation facilities, that are also highly monochromatic and have a low divergence, are highly suitable tools forexamining fragile, valuable and/or unique artefacts withminimal or no damage. We can achieve information about the major- and trace-level composition of the objects, about the chemical state of one or more atomic species that are present and/or about crystallographic phases on the materials.

Since the materials and objects encountered in the field of art-analysis, archaeology and conservation are oftencomplex in shape, covered with alteration layers and/or maybe highly heterogeneous, the use of X-ray micro beams isvery often required to allow for the measurement of localrather 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)

AppliedAppliedApplied techniquestechniquestechniquesElemental microanalysis down to the sub-ppm level is possible bymeans of µ-XRF (X-ray fluorescence analysis).

Local chemical state determinations of selected (trace) constituentsare possible by applying XAFS and µ-XAFS (X-ray absorptionspectroscopy)

Information on the presence and nature of crystalline phases can beobtained via XRD (X-ray diffraction), which usually employ X-rayphotons with energies in the 0.5 to 30 keV range.

Alternatively, entire objects may be bathed in highly-energeticsynchrotron beams to allow high quality radiographic or tomographicimaging measurements, revealing the internal structure of theseartefacts.

XRD applicationsat SRA2005

Manufacturing Manufacturing cosmeticscosmetics in in ancientancient EgyptEgypt

artificially synthesized !

Mural painting representing an eagle-knight, probably a religious symbol (Cacaxtla, Tlaxcala, Mexico)

Pottery vase representing Tlàloc, the Mayan god of rain (Templo Mayor museum , Mexico).

MAYA BLUE PIGMENT[G. Chiari, R. Giustetto, G. Ricchiardi (2003) Eur. J. Mineral. 15:21-33]

G. Chiari (2005) IUCr, 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 (SEM image, 3520X)

Quartieri - SILS 2006 NapoliIndigo molecule

INDIGOINDIGO

The Mayas extracted it from the leaves of Indigofera suffruticosa

Orthorombic Palygorskite projected on (001) face

MAYA BLUE PIGMENT ?

SR X-ray powder diffraction at GILDA beamline

Electron Density map at the level of indigo

Indigo

MODEL OF ENCAPSULATION OF INDIGO IN THE PALYGORSKITE FRAMEWORK

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

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 Maya Blue depends upon a very long series 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 water loss at 120<T<300°C (ZEOLITIC ZEOLITIC water) is the same for both materials. It makes sense if indigo does not enterdoes not enterthe channels.

The ADSORBEDADSORBED water loss at low temperature (<120°C) is much higher for palygorskite than for MB. It makes sense if indigo occupies the grooves instead of water.

A new theory is needed:A new theory is needed:Indigo does not go inside the channels but Indigo does not go inside the channels but only fills the grooves all around the crystalonly fills the grooves all around the crystal

Indigo

The indigo molecule is imbedded into the channel. 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.

XAFS spectroscopy is a potentially very useful technique tobe applied in archaeological studies.

It is a non-destructive method which can be applied in air; itvirtually does not require any restriction on the type and size of the sample, which can be metal, ceramic, glass, cloth etc. and, finally, 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 preciouscultural heritage made of very different materials.

Archaeometrical applications of X-ray Absorption Spectroscopy

The The originorigin of color in of color in ancientancient glassglass

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

They are usually transition elementswhich absorb characteristic frequencies

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 oxidation state on the color of the studied samples

- to identify the possible decolorant role of manganese oxide in the almost uncoloredsamples

The Fe and Mn K-edge XANES spectra were collected directlyon the glass fragments in the fluorescence mode on the GILDA-CRG beamline (ESRF).

A dynamically sagittally-focussing monochromator withSi(311) crystals and a 13-element high-purity Ge detector were used.

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 — 0.99

B 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