multi-analytical study of historical semiconductor pigments · gamblin artists’ color 1841: the...
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Valentina Capogrosso1, Daniela Comelli1, Austin Nevin2, Sara Bellei2, Anna Cesaratto1,
Gianluca Valentini1
1Dipartimento di Fisica, Politecnico di Milano 2Istituto di Fotonica e Nanotecnologie, Consiglio Nazionale della Ricerca, (IFN-CNR)
Multi-analytical study of historical semiconductor pigments
Multidisciplinary approach at ArtIS Lab
Main objectives:
• to map the presence of materials on surfaces of artworks
• to investigate degradation and stability
• to understand physical and chemical properties of historical and modern materials
• to aid conservation in its broadest sense
The ArtIS Lab (Imaging and Spectroscopy for Art Conservation)
• Joint laboratory of Dept of Physics - Polimi and IFN – CNR
• Expertise in:
Physics, Engineering, Chemistry, Material Science
between 19th-20th Centuries: a new class of pigments
Ultramarine blue
Chrome yellow
Cadmium yellow
Viridian green
Zinc white
Model for a typical artists’ palette from the end of the
20th century
image courtesy from Gamblin Artists’ Color
www.gamblincolors.com
1841: the american artist John Goffe Rand invents
the squeezable metal tube
Still Life with Cabbage by James Ensor (ca.1921) Geert Van der Snickt et al., Analytical Chemistry 81, 2009
CdS
Still Life with Three Fish by Pablo Picasso, 1946 Francesca Casadio, Volker Rose, Applied Physics A, 2013
Zn-based white
Six historical lithopone samples produced at the beginning of the 2oth Century, provided us by McCrone Associates, Inc.
(www.mccroneassociates.com)
• Krebs Pigment and Chemical Co, Delware
(now Du Pont)
• New Jersey Zinc company (now Horsehead Co.)
I case study: historical lithopone white pigment
Krebs Pigment & Chemical Co Delware, 1898
www.dupont.com
Franklin city New Jersey Zinc Company, 1907
www.horsehead.com
BaS + ZnSO4 = ZnS + BaSO4 (Crude Lithopone)
What lithopone is? historical synthesis process in the United States
1894 Franklin
Mine
BaSO4+2C=BaS+2CO2 ZnS+H2SO4+1/2O2=ZnSO4+H2O+S
Spharelite Zn(S,Fe)
Baryte (BaSO4)
- Calcined @(600-900)°C - Filtred, dried and pulverized
LITHOPONE PIGMENT
• cheap • non toxic
• good coloring and covering properties • easy in mixing with all vehicles and pigments
SPHARELITE Zn(S,Fe) from franklin mine, New Jersey
image courtesy from www.fluomin.org
…what happens if impurities are not completely eliminated during the
synthesis of the pigment?
raw materials…and their impurities!!!
…same stone, under UV light!
Mn2+
Cu2+ Cu+
EC
EV
e- e-
4T1
6A1
(Mn2+)
CuZn2+
Ag2+
D
GL
(530 n
m)
Cui+
BL
(476 n
m)
OL
(580 n
m)
BL
(470 n
m)
• ZnS is a semiconductor • Eg=344 nm
• can host different metal ions which act as luminescent centres
“Breton women” Vincent Van Gogh, Arles, December 1888,
watercolour, 74 x 60 cm, Modern Art Gallery Milano
RGB color map of the UV-induced emission
ZnS:Cu
ms decay map of the luminescence
…luminescence properties are preserved!
D. Comelli et al., “On the discovery of an unusual luminescent pigment in van Gogh’s painting Les bretonnes et le pardon de pont Aven” Appl. Phys. A, Nov. 2011
multispectral fluorescence micro-imaging: experimental setup
CCD
l
RGB map reconstructed
IF FILTER
7 IF FILTERS:
(400-700) nm set
(50 nm step)
SAMPLE
OBJECTIVE LENS
(20 x)
LIGHT
SOURCE
(Mercury
lamp line
@ 365 nm)
MICROSCOPE
Fluorescence temporal decay An UV pulsed laser source excites fluorescence of an area of interest…
… fluorescence decays following an exponential law…
… by using a time-gated ICCD, we record images at different delays (with respect to laser pulses) …
… through linear algebra it is possible to reconstruct a map of the fluorescence lifetime from each pixel in an image
time (ns)
The lifetime map allows one to distinguish the presence of different fluorescent compounds in the analyzed area
Fluorescence Lifetime Imaging (FLIM)
A = fluorescence amplitude
τ = fluorescence
lifetime
I t( ) = A ×e-t t
In
ten
sit
y
Lifetime map [ns]
900
0
tdecay=0 ns tdecay=10 ns tdecay=1000 ns
Q-switching laser
@365 nm, 1ns
RGB map
t map (from 100 to
9000 ns)
Electron Paramagnetic Resonance (EPR) measurements confirmed the
presence of impurities and provided information on the micro-
environment of defects in the ZnS crystalline lattice, revealing as a very
efficient tool for quantitative analysis
…Measurements on lithopone…
II Case study: Zn-based paints @ Soleil
Analysis of an historical W&N ZnO paint tube from the Courtauld Art Institute of London
Synchrotron radiation techniques allow micrometric spatial resolution and sub-ppm sensitivity !
LUCIA beamline at Soleil Line for Ultimate Characterization by Imaging and Absorption
Analysis was undertaken with Laura Cartechini and Francesca Gabrieli (ISTM-CNR)
LUCIA is a "tender" X‐ray microprobe designed
for chemical speciation
Energy range: 0.8 – 8 keV
Beam spot: 3x3 µ2
µ-XRF: measurement of the fluorescence spectra with a 4-elements SDD (silicon drift diode) µ-XAS: measurement of the fluorescence yield (FY), of the sample drain current (TEY) and measurement of the transmitted photons flux (diode)
vaccum chamber with an (x,y,z) stage
Powder pellets have been prepared on a boron
nitride substrate
Micro-XRF spectra
Cl S
Si
K
Sn
Cr
Fe
Ba Zn
Ca
Ephoton = 8 keV
Energy (keV)
XRF data treated by means of PyMca software
Micro-XANES spectra
Ba
Cr
Anal. Chem. 2011, 83, 1214–1223
Cr K-edge XANES measurements
Micro-XANES spectra
Ba
Cr
Anal. Chem. 2011, 83, 1214–1223
Cr K-edge XANES measurements
Acknowledgements
Sara Bellei
PROJECTS:
FUTURAHMA: Futurism. Research, Art History and Material Analysis (2013-2016) funded
by the Italian Ministry of Education
F. Rosi, L. Cartechini, F. Gabrieli, Istituto di Scienze e Tecnologie molecolari (ISTM-CNR)
Italy-USA bilateral: Lo sviluppo e l'integrazione di metodi complementari di imaging e di
micro-analisi per lo studio di dipinti funded by Italian Ministry of Foreign Affairs
LeadART: Induced decay and ageing mechanisms in paintings: focus on interactions
between pigments and organic binders (JPI EU Project)
Laboratoire de Spectrochimie Infrarouge et Raman, Université de Lille-1 Sciences et Technologies,
(France)
Italy-Egypt bilateral: Study of objects and materials from the Egyptian archaeological
heritage funded by Italian Ministry of Foreign Affairs
