Microdiffraction and microfluorescence study of

Mesoamerican mural paintings

M. Sánchez del RíoUAM-I Mexico D.F.

P. Martinetto, E. Dooryhée CNRS, Grenoble France

C. Reyes-ValerioINAH, Mexico

International Conference on X-ray Optics and Microanalysis

Frascati 26-30 September 2005.

Mural Paint• CaO (lime) + H2O-> Ca(OH)2 (slaked lime) • painted in wet (buon fresco). • Ca(OH)2 + CO2 → CaCO3 (crystallization) +

H2O• Colors must bind perfectly (minerals

preferred)• Requires elaborated technology in

materials (preparation of plaster and pigments) and high artistic capabilities

• Mesoamerican artists arrived to a high degree of expertise in the fresco technique, in prehispanic times, followed by colonial paint, and continued by XX c. artists, like Rivera, Orozco, Siqueiros, …

Mortar

Plaster Ca(OH)2

Crystalline layer CaCO3

μ−fluorescence or PIXE

2 pre-Hispanic samples studied

Tamuin and Cacaxtla

X-ray beam direction

Light sources for illuminating the sample for the optical microscope

Optical microscope head

X-ray detector

Tamuin

Cacaxtla

M. Sanchez del Rio, P. Martinetto, A. Somogyi, C. Reyes-Valerio, E. Dooryhée, N. Peltier, L. Alianelli, B. Moignard, L. Pichon, T. Calligaro, J.-C. Dran "Microanalysis study of archaeological mural samples containing Maya blue pigment" Spectrochimica Acta B 59 (2004) 1619-162

00

1 200

00 1

1 2

( ) ( )( ) 1 expsin sin( ) 1

( ) ( )4 ( ) sinsin sin

ell

el

XRFl

lPE

E EE dEI I E EE

C μ μμψ ψσ

μ μπ σ ψψ ψ

⎧ ⎫⎡ ⎤⎛ ⎞⎪ ⎪− − +⎨ ⎬⎢ ⎥⎜ ⎟Ω ⎝ ⎠⎪ ⎪⎣ ⎦⎩ ⎭=

+

REF: Lachance G.R. and Claisse F., Quantitative x-ray fluorescence analysis. Theory and applications, John Wiley, 1995

XRF “Simple” XRF quantificationto obtain absolute concentrations

PIXE: Ca in mural paint (prehispanic/colonial)

~40% in “fresco”, like in CaCO3

We found Ca concentrations from 30 to 50% in most samples, indicating that the fresco technique was used.

Two exceptions should be noted: the blue pigment in a Cacaxtla cornice (not coming from a mural) and the mural sample from Santa Cecilia Acatitlán. Clearly, a low calcium concentration means that the samples were not prepared using the fresco technique.

20 CaK

0100000200000300000400000500000600000700000

Jiu(

MB

50)

Tot(5

1)

Tot(5

2)

Tot(5

3)

Tez(

B54

)

Tez(

B55

)

Tez(

G56

)

Tez(

G57

)

Cua

(61)

Cua

(62)

CU

A(0

46)

CU

A(0

47)

Ca(

DB

5)

Ca(

DB

6)

CA

(DB

116)

CA

(DB

117)

CA

(DB

237)

CA

(DB

238)

CA

(LB

239)

CA

(LB

240)

Ca(

LB7)

Ca(

LB8)

CaC

or(9

)

CaC

or(1

0)

Cec

(63)

Cec

(64)

Cec

(65)

Cec

(66)

Cec

(P69

)

Cec

(P70

)

TAM

(27)

TAM

(28)

TAJ(

49)

TAJ(

50)

TAJ(

51)

TAJ(

53)

TAC

(55)

TAM

(BL3

0)

TAM

(LB

31)

Bo(

12)

Bo(

13)

Bo(

14)

Bo(

Bc1

9)

Bo(

Bc2

0)

Bo(

Bc2

1)

Bo(

G22

)

Bo(

G23

)

M. Sanchez del Rio, P. Martinetto, C. Solis and C. Reyes-Valerio “PIXE analysis in Maya blue in prehispanic and colonial mural samples" Submitted to NIMB at the proceedings of the International Conference on Ion Beam Analysis (IBA2005) Sevile, June 2005

XRD @ ESRF/ID18F• Local information on the

crystallographic phases • Qualitative analysis:

Pigment identification• Quantitative analysis: percent of

each phase (In progress)• Grazing incidence

(thick samples)• Focused (CRL) 10 X 1 μm2

• Unfocused (approx. 50 X 50 μm2) • Sample-Detector (MARCCD 165)

D~10 cm• Standard (Quartz) for D, and beam

center…

SR beam 10 keV

Sample

Sensibility test: Hematite on lime

Pigments/Phases

• CaCO3, Quartz, etc• Unknown (restoration?) • Red -> hematite• Blue -> Palygorskite (Maya blue)

Maya blue• Artificial organo-clay pigment

(palygorskite+indigo)

• Light blue (or turquoise) color

• Extreme resistance to acids and chemicals (<300 º C) and biodegradation

• Commonly used by Mayas and other people in Mesoamerica (≤VIII? -XV). Used during the colonization until 1580? and in Cuba (XVIII,XIX c.)

• Found in paints (murals), pottery, texts (codices), sculptures and ceremonial and funeral objects.

Archaeological context

• Commonly used by Mayas and other people in Mesoamerica (≤VIII? -XV).

• Found in paints (murals), pottery, texts (codices) , sculptures and ceremonial and funeral objects.

• Used during colonization in convents and churches until 1580. Also found in colonial paints in Cuba (XVIII-XIX)

• Rediscovered in 1932 (Merwin). Composition known since the 1960’s.

• Recent interest in chemistry and possible new applications.

Open questions on Maya blue• Chemical point of view: unknown origin of

stability. It has been suggested that the indigo molecules seal the clay channels or enter into them. What is the mechanism of the chemical interaction? Why is so resistant?

• Anthropological and historic context:• Origin, manufacture and diffusion (traded

pigment and/or materials or technology). • Sources of palygorskite• Artistic techniques (fresco, mixing and

combining pigments, etc.)• Dating artworks (high uncertainties)• Why it disappeared around 1580 in Mexico?• Cuba …

Bonampak green:

No Cu Co found!

Same technology as blue?

Bonampak green: Same technology as blue? Probably YES

Crystallographic structure• 1940 Bradley: Monoclinic C2/m

trioctahedralSi8Mg5O20(OH)2(OH2)4 4H2O

• 1966 Dritz and Alexandrova: dioctahedral model Mg4Si8…

• 1992 Chisholm: mixture of two phases: monoclinic (C2/m) and orthorrombic (Pbmn)

• “Theoretical formula”: Si8Mg2Al2O20(OH)2(OH2)4 4H2O

• No Rietveld refinement is done with a structure consistent with the chemical analysis.

ESRF/BM01B: XRD on palygorskite series λ=0.8Å

PTAl1.89Fe0.03Mg1.93Si8.06Al0.00Lisboa(PT)

BERAl1.60Fe0.39Mg1.98Si7.90Al0.12Bercimuel(SG, ESP)

MEXAl1.57Fe0.24Mg2.21Si7.85Al0.15Yucatan (MEX)

TORAl1.48Fe0.37Mg2.25Si7.91Al0.09Torrejon(CC, ESP)

USAAl1.47Fe0.25Mg2.30Si7.85Al0.14Attapulgus(USA)

AL1Al1.20Fe0.16Mg2.89Si8.02Al0.01Los Trancos(Al, ESP)

SPAl1.15Fe0.18Mg3.01Si7.91Al0.09Esquivias(M, ESP)

codeoctatetraOrigin

1.00

2.00

3.00

4.00

5.00

6.00

12.600 12.800 13.000 13.200 13.400 13.600

T.P.

ESRF/BM01B: XRD on palygorskite series

λ=0.8Å

a-axis [Å]

[Mg+

Fe] oc

t

M. Suarez, E. García-Romero, M. Sanchez del Rio, P.Martinetto and E. Dooryhée, “ON THE STRUCTURE OF PALYGORSKITES: CELL PARAMETERS’ DEPENDENCE ON THE OCTAHEDRAL CONTENTS” To be submitted

Conclusions and future work• μ(XRD+XRF) are efficient techniques for pigment identification and

quantitative analysis– Local distribution– Thin cross sections (depth)

• Unambigously found palygorskite in Bonampak’s green, suggesting a fabrication process similar to Maya blue

• New samples from Bonampak will be collected soon

• The chemistry of Maya blue is being studied by other techniques (Raman, FTIR, NMR, etc)

• The great number of images (7DVD) needs ad-hoc software for data managing, visualization, analysis, and quantitative fitting of the diffractographs.