p. gaugin: by the seashore, martinique. oil on canvas ...€¦ · detect forged paintings assign...

|| 1.12.2015Emmanuel Wirth und Tobias Wyler 1

Analytical Strategy: Art

P. Gaugin: By the Seashore, Martinique. Oil on Canvas, 1887

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

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

Challenges in Analysing Paintings

How old is the painting?

Who is the alleged artist?

Who where previous owners?

Previous appearance in art literature

Detective work

Analysis: ask the obvious

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

What can we analyse?

Stratigraphic Analysis

Cross-section reveals layers

Chemical analysis:

Pigments

Binders

What can we analyse?

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

Signature of a Painting

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

Photographing the Entire Painting

UV irratiation + visible light photography

Old pigments tend to fluoresce

Modern, aromatic organic pigments fluoresce strongly

Restoration works are highlighted

Photographing the Entire Painting (2)

Still life with flowers. Oil on canvas. 20th century, Ireland. Left: visible light. Right: UV fluorescence photography

Perry’s house at

Newcastle. Oil on

canvas. 20th century.

Top: visible light

Bottom: IR photography

Baptism of Jesus. Panel Tempera Painting, 1685, Poland. Left: visible light. Right: X-ray photography

Pigments

Elements

Organics

Metallorganics

Pigment and Binder Determination

Hansa Yellow 16

Copper phthalocyanine

TiO2 (anatase, rutile)

«Titanium White»

CdS«Cadmium Yellow»

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

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

Non invasive

Raman for organics (characteristic spectrum)

XRF, XRD for metals

Invasive methods

Analytical Methods for Individual Pigments

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

Rayleigh

Stokes

Raman: How does it work?

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)

Raman Instrument

High spatial resolution of 1 µm

Can be done directly on painting

Portable instruments available

Raman Microscopy

Raman microscopy on a painting.

Raman microscopy on a

painting.

Raman Spectra

X-Ray Fluorescence

Suited for the identification of

elements

Limited to elements with

mass 23 or higher

X-Ray Fluorescence

Spot analysis

Imaging whole painting

for one element

(emission line)

Monochromatic X-ray source

Characteristic diffraction pattern

Potential to be conducted on-site

Reveals polymorphs, not just elements

example TiO2 (rutile vs anatase)

X-Ray Diffraction

X-ray diffraction pattern of powdered Cd orange pigment

(source: Getty)

X-Ray Diffraction

XRF/XRD portable

device (Getty)

ATR-IR

X-ray powder diffraction

Chemical analysis: solubility, elemental analysis methods

Destructive Methods

Combine complementary data from XRF, Raman, (XRD),

expert analysis, UV/IR/X-ray photography

By computer, since lots of data points

The Full Picture

(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…

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

Sources

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

Sources (2)

P. Picasso: The Old Guitarist,

1904, oil on panel.The Old Guitarist, IR

reflectogram

The Old Guitarist, radiography

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

Photographing the Entire Painting

Anthony van Dyck, Saint Rosalie praying for

the Plague stricken of Palermo 1624Radiograph

Third autoradiograph4-5h after irradtion

54Mn, t1/2 = 2.6h

Umber contains MnO

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

Eighth autoradiograph8-20d after irradtion

32P, t1/2 = 14.3d

Bone black contains

phosphates

Anthony van Dyck

p. gaugin: by the seashore, martinique. oil on canvas ...€¦ · detect forged paintings assign...

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