p. gaugin: by the seashore, martinique. oil on canvas ...€¦ · detect forged paintings assign...
TRANSCRIPT
|| 1.12.2015Emmanuel Wirth und Tobias Wyler 1
Analytical Strategy: Art
P. Gaugin: By the Seashore, Martinique. Oil on Canvas, 1887
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Detect forged paintings
Assign painter to unknown painting
Find inconsistencies in order to refute hypothesis
(cannot prove origin)
1.12.2015Emmanuel Wirth und Tobias Wyler 2
Questions
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Size of painting (often large)
Surface structure (often rough)
Restoration works may mask painting
Older paintings underneath painting
Potentially high-value, unique
Usually only non-invasive methods are used
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Challenges in Analysing Paintings
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How old is the painting?
Who is the alleged artist?
Who where previous owners?
Previous appearance in art literature
Detective work
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Analysis: ask the obvious
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The physical painting:
Frame and canvas/wood
Style: brush strokes, colour scheme, contours, contrast, etc.
Signature
Microscopy (wood/canvas or surface of painting)
Restoration works
The picture:
Top layer
Underlying layers
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What can we analyse?
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Stratigraphic Analysis
Cross-section reveals layers
Chemical analysis:
Pigments
Binders
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What can we analyse?
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Attractive target for analysis:
Very characteristic to an artist (but can change throughout life)
On the top layer, therefore accessible
Some artists may have used the same paint to sign different
paintings
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Signature of a Painting
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Getting a fresh perspective:
X-ray transmission photography
Highlights underpaintings, certain paints
Hints towards certain pigments (e.g. Pb white)
IR irradiation + IR photography
sketching below paint
cracks in dry paint
Restoration work stands out
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Photographing the Entire Painting
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UV irratiation + visible light photography
Old pigments tend to fluoresce
Modern, aromatic organic pigments fluoresce strongly
Restoration works are highlighted
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Photographing the Entire Painting (2)
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Still life with flowers. Oil on canvas. 20th century, Ireland. Left: visible light. Right: UV fluorescence photography
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Perry’s house at
Newcastle. Oil on
canvas. 20th century.
Top: visible light
Bottom: IR photography
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Baptism of Jesus. Panel Tempera Painting, 1685, Poland. Left: visible light. Right: X-ray photography
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Pigments
Elements
Organics
Metallorganics
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Pigment and Binder Determination
Hansa Yellow 16
Copper phthalocyanine
TiO2 (anatase, rutile)
«Titanium White»
CdS«Cadmium Yellow»
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Pigment and Binder Determination
Binders
Binding medium
Increases lifetime
Often emulsions
Drying / curing
Chalk, Clay, animal fat
Egg Tempera
Natural oils such linseed oil or poppy oil
Synthetic, petroleum based
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Linseed Oil: unsaturated fatty acids
can be oxidised by oxygen undergo
radical polymerization
Alkyde Resin: Polyesters that form
during drying. Monomers include
phthalic anhydride and glycerol.
Additives such as styrene and abietic
acid are used.
Acryl Resin: Polymers that are
based on acrylic acid or methacrylic
acid, used in water based colors
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Non invasive
Raman for organics (characteristic spectrum)
XRF, XRD for metals
Invasive methods
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Analytical Methods for Individual Pigments
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Raman: How does it work?
(1) Laser light excites the sample.
(2) This light is scattered in all directions
(3) A detector records the Raman spectrum (vis-IR range is scanned)
(4) This spectrum shows light at the original laser (or Rayleigh) frequency and the
Raman spectral features unique to the sample
frequency
inte
nsity
Rayleigh
Stokes
Raman
Anti-
Stokes
Raman
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Raman: How does it work?
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Dispersive (using a grating) vs. FT-Raman
Diode-Laser (wavelength could in theory be anything from
UV up to IR)
Raman scatter yield higher at lower wavelengths
Fluorescence too high at lower wavelengths
CCD (charge coupled device) or PMT (photomultiplier
tubes)
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Raman Instrument
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High spatial resolution of 1 µm
Can be done directly on painting
Portable instruments available
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Raman Microscopy
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Raman microscopy on a painting.
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Raman microscopy on a
painting.
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Raman Spectra
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X-Ray Fluorescence
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X-Ray Fluorescence
Suited for the identification of
elements
Limited to elements with
mass 23 or higher
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X-Ray Fluorescence
Spot analysis
Imaging whole painting
for one element
(emission line)
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Monochromatic X-ray source
Characteristic diffraction pattern
Potential to be conducted on-site
Reveals polymorphs, not just elements
example TiO2 (rutile vs anatase)
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X-Ray Diffraction
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X-ray diffraction pattern of powdered Cd orange pigment
(source: Getty)
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X-Ray Diffraction
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XRF/XRD portable
device (Getty)
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LC
ATR-IR
X-ray powder diffraction
Chemical analysis: solubility, elemental analysis methods
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Destructive Methods
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Combine complementary data from XRF, Raman, (XRD),
expert analysis, UV/IR/X-ray photography
By computer, since lots of data points
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The Full Picture
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(Allegedly) Gauguin
View of Notre Dame, 1871, signed by P Gaugin Detail of the signature
Traces of of titanium and copper were found in the signature. Both titanium white
and copper phthalocyanine were not on the market until the 20th century…
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P. Gaugin: By the Seashore, Martinique. Oil on
Canvas, 1887. wikimedia.org
http://artnewengland.com/images/2015/06/PAINTING-ON-
RAMAN.JPG
https://www.bruker.com/fileadmin/user_upload/1-
Products/X-
rayDiffraction_ElementalAnalysis/mXRF/artax_painting_c
osimo.jpg
https://www.getty.edu/conservation/about/science/portable
_xrd_xrf.pdf
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Sources
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http://fineartconservation.ie/ultraviolet-radiation-4-4-
43.html
http://fineartconservation.ie/infrared-radiation-4-4-44.html
http://fineartconservation.ie/x-radiography-4-4-45.html
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Sources (2)
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P. Picasso: The Old Guitarist,
1904, oil on panel.The Old Guitarist, IR
reflectogram
The Old Guitarist, radiography
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Neutron activation autoradiography
Reveals isotopes/elements of paints used
Underlying images
Expensive
Need thermal neutron source (nuclear power plant)
Need to wait several weeks for longest-lived isotopes
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Photographing the Entire Painting
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Anthony van Dyck, Saint Rosalie praying for
the Plague stricken of Palermo 1624Radiograph
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Third autoradiograph4-5h after irradtion
54Mn, t1/2 = 2.6h
Umber contains MnO
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Sixth autoradiograph2-4d after irradtion
64Cu, t1/2 = 12.8h
azurite consists of
CuCO3Cu(OH)2
24Na, t1/2 = 15h
Ultramarine consists of
sodium aluminosilicate
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Eighth autoradiograph8-20d after irradtion
32P, t1/2 = 14.3d
Bone black contains
phosphates
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Anthony van Dyck