Post on 22-Feb-2023
Variable-‐temperature Micro-‐Raman Spectra of Ar6sts’ Pigments:
Cadmium Yellow (CdS) Chrome Yellow (PbCrO4)
and Maya Blue Jacqueline Wagner Riddle
Prof. I.S. Butler Emily Hopkins
96th Canadian Chemistry Conference and ExhibiMon Quebec City, 30 May 2013, 9 am
Spectroscopy in art conservaMon
• Knowledge of arMfact composiMon
• StabilizaMon without further damage – Temperature, humidity and light exposure controlled
• IdenMficaMon of forgeries
Some recent work
• Lead chromate (PbCrO4) – High-‐pressure Raman study by Bandiello et al. (2012)
• Cadmium sulphide (CdS) – Temperature-‐dependent (-‐258 to 42˚C) Raman study of CdS quantum dots by Neto et al. (2012)
• Maya blue – Ambient-‐temperature Raman study of Maya blue pigments in different clay structures by Sanchez del Rio et al. (2006)
Instrument SpecificaMons • inVia Renishaw microscope system • Long-‐working distance lens (50X/0.75) • 514-‐nm (16 mW) and 785-‐nm lasers
• Linkam THMS600 temperature stage
CdS and PbCrO4 Pigment InformaMon Cadmium Yellow (CdS) • Hexagonal wurtzite polymorph,
occurs naturally as Greenockite • Used in photoresistors, solar cells • Commercially available starMng 1840 • Used by Monet, van Gogh, MaMsse
Chrome Yellow (PbCrO4) • Occurs naturally as
crocoite (monoclinic prismaMc)
• The colour associated with school buses
CdS Raman spectrum 514 nm laser, 5% of 16mW
• 301 and 603 cm-‐1 corresponding to the longitudinal phonon mode (1-‐LO) and its overtone (2-‐LO)
• 906 cm-‐1 peak corresponding to second overtone (3-‐LO), now visible due to resonance Raman effect
1-‐LO
2-‐LO
3-‐LO
CdS Temperature dependency of peak posiMon 514 nm laser, 5% of 16mW
Overall shihs for the 1-‐LO, 2-‐LO and 3-‐LO (not
shown here) peaks in the
temperature range are
–8.1, –17.7, and –22.4 cm-‐1.
!""# $""# %""# &""# '""# (""# )""# *""# +"""# ++""#
!"#"$%&$'($)&'*%+",-.%/$&')0%
!"#"$%)1&2%+3#450%
6"7#&/#%8/9:1&7(%;",&"-9(4<(#:(,"'/,(%!"#"$%8'/7*%
&"","#-.#
%&","#-.#
%"","#-.#
$&","#-.#
$"","#-.#
!&","#-.#
!"","#-.#
+&","#-.#
+"","#-.#
&","#-.#
!&,+#-.#
!""# $""# %""# &""# '""# (""# )""# *""# +"""# ++""#
!"#"$%&$'($)&'*%+",-.%/$&')0%
!"#"$%)1&2%+3#450%
6"7#&/#%8/9:1&7(%;",&"-9(4<(#:(,"'/,(%!"#"$%8'/7*%
&"","#-.#
%&","#-.#
%"","#-.#
$&","#-.#
$"","#-.#
!&","#-.#
!"","#-.#
+&","#-.#
+"","#-.#
&","#-.#
!&,+#-.#
Raman shiD (cm-‐1)
CdS Temperature dependency of FWHM
• The 1-‐LO and 2-‐LO bands broaden with increasing temperature
Raman spectrum of PbCrO4 at 25˚C 785 nm laser, 20% power
• 840 cm-‐1 (s) peak corresponding to v1 symmetric stretching of CrO4
2-‐ • 856 cm-‐1 (overlap)
• 337, 357, 376, 399 cm-‐1 v4 and ν2 bending modes
Maya Blue Pigment History
• Used by the ancient Mayans on polery, sculptures, murals
• Associated with sacrifices and offerings
• Resistant to acids, alkalis, solvents, oxidants, reducing agents, moderate heat and biocorrosion
Mechanochemical Synthesis of Maya blue
• syntheMc indigo and sepiolite (Mg4Si6O15(OH)2·∙6H2O)
purchased from Sigma-‐Aldrich
• A mixture of indigo (2%) and sepiolite (98%) was placed in a ball milling jar and milled for 0.5 hours
From the top: structure of indigo; encapsulaMon of indigo molecule inside a sepiolite tunnel (with dashed lines indicate H-‐bonding between the indigo C=O group and the clay OH2) Image from Giuste6o et al., 2010.
Raman spectra of indigo and Maya blue at 25 °C
• AcMvaMon of vibraMonal modes with Bu symmetry due to the deformaMon of indigo in the sepiolite framework
Conclusions • Cadmium Sulphide (CdS) – Peaks redshih and broaden with increasing temp.
• Chrome Yellow (PbCrO4) – Broadening and amorphizaMon with increasing temp.
• Maya Blue – No change up to 250˚C
Three very stable pigments!
Acknowledgments Thanks to Prof. I.S. Butler, Emily Hopkins, Yann Desjardins-‐
Langlais, Julia Bayne, and Joël Poisson. Thanks to NSERC for financial support used toward the Raman microscope and materials.
Contact informa6on: Jacqueline Riddle jacqueline.riddle@mail.mcgill.ca
Ian S. Butler ian.butler@mcgill.ca
References Arnold, D., et al., An<quity, 2008, 82, 151–164. Bandiello, E., et al., Physical Review B, 2012, 85, 024108. Giustelo, R., et al. Periodico di Mineralogia, 2010, Special Issue, 21-‐37. Gonzalez-‐Alcudia, M., et al., Adv. Tech. Mater. & Mater. Proc. J., 2007, 9, 81-‐86.
Kleber, R., et al., Studies in conserva<on, 1967, 12 (2), 41-‐56. Neto, E., et al., Nanotechnology, 2012, 23, 125701-‐125709. Frost, R., J. Raman Spectrosc., 2004, 35 (2), 153-‐158. Leona, M., et al., Journal of the American Ins<tute for Conserva<on, 2004, 43 (1), 39-‐54.
Sanchez del Rio, M., et al., J. Raman Spectrosc. 2006, 37, 1046-‐1053.
Raman spectra of indigo and Maya blue at 25 °C
• AcMvaMon of vibraMonal modes with Bu symmetry due to the deformaMon of indigo in the sepiolite framework
1633 1380 1380
Raman shih (cm-‐1)
Indigo
Maya Blue
1680
Raman spectrum, 514 nm laser of PbCrO4 • 840 cm-‐1 (s) peak corresponding to v1 symmetric stretching of CrO4
• 856 cm-‐1 (overlap) second v1 band
• 337, 357, 376, 399 cm-‐1 v4 and ν2 bending modes
• 1672 cm-‐1 overtone of v1 symm. stretch
!"
#!!!!"
$!!!!!"
$#!!!!"
%!!!!!"
%#!!!!"
$!!" &!!" #!!" '!!" (!!" $$!!" $&!!" $#!!" $'!!" $(!!"
!"#"$%&'()%*+#,-.%