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Van Gogh’s HiddenVan Gogh s Hidden PicturesPictures
Koral Modi
How is chemistry used to analyze art?How is chemistry used to analyze art?
• One example: Raman Spectroscopy– When a laser beam hits the surface of a painting, p g,the frequency of the photons in the laser beam change based on what type of material they hit g yp y
– Since each color of paint consists of different l t th h t h t diff telements, the photons change to different frequencies based on the color of the paint they hit d i thi i ti t fi t h thit, and in this way, scientists can figure out what color paint was used in the painting.
– The unique frequency created by different materials is called the Raman Spectrum
• However, the intense light beams used in Raman Spectroscopy can often damage the paints used by earlier artists, so there is a limit to how much analysis can be done using Raman SpectroscopyRaman Spectroscopy
• A similar technique, called X‐ray fluorescence d di V G h’spectroscopy, was used to discover Van Gogh’s
hidden pictures. – X‐ray fluorescence spectroscopy penetrates a painting much better than Raman Spectroscopy or p g p pytraditional X‐ray radiography
Van Gogh’s backgroundVan Gogh s background
i h b h th• Vincent Van Gogh was born on March 30th, 1853 in the southern Netherlands
• From 1860 to 1880, Van Gogh unsuccessfully worked as a clerk in a bookstore, an art ,salesman and a preacher, before becoming an artist
• When he first started painting, he used a somber palette that consisted of dark earthysomber palette that consisted of dark, earthy tones and dull grays
Th P t t E t V G h A il 1885The Potato Eaters, Van Gogh, April 1885
• Van Gogh’s early paintings did not sell well. g y p gHis brother Theo, an art dealer in Paris, told him it was because people were morehim it was because people were more attracted to the bold Impressionistic style at the timethe time.
• In March 1866, Van Gogh moved into his brother’s apartment in Paris. There, he was immediately attracted to the work of theimmediately attracted to the work of the Impressionists, such as Adolphe Monticelli, Monet and DegasMonet, and Degas
Van Gogh’s Hidden PaintingsVan Gogh s Hidden Paintings
I i d b th I i i t b t t• Inspired by the Impressionists, but too destitute to buy new canvases to accommodate his new paintings Van Goghaccommodate his new paintings, Van Gogh was sometimes forced to paint over his old works to save money creating “hiddenworks to save money, creating hidden paintings”
• Experts estimate that Van Gogh painted overExperts estimate that Van Gogh painted over 1/3 of his older works.
• The best known hidden painting is “Patch of• The best known hidden painting is Patch of Grass”
Patch of Grass, Van Gogh, 1877
Hidden Picture behind “Patch of Grass”
X‐Ray Fluorescence Spectroscopy: Overview
• Purpose: To non‐destructively measure the elemental composition of a sample.p p
A li i Mi i G l i S di• Applications: Mining, Geologic Studies, Ceramics/Glass, Petroleum, Artwork
Morgan Dundon
Overview ContinuedOverview Continued
• Where can these samples be analyzed?samples be analyzed?
‐Museums‐Research Centers
XRF spectrometer
Process of XRFProcess of XRF
• The x‐ray is absorbed or scattered through material.
Ph l i Eff k l h h• Photoelectric Effect takes place throughout the entire process
ProcessProcess
• Shells labeled K, L, M, and N.
• X‐ray excitation source strikes sample
• Electron in K shell is ejected! (createsElectron in K shell is ejected! (creates instability)
Continued…Continued
l f h ll fill h• Electron from L or M shell fills the vacancy
• X‐ray (unique to the element) is emitted.
• Another vacancy created…..Electron from M f ll hor N now fills this
• A ray emitted once again
Vacancies Filled!Vacancies Filled!
Auger ElectronAuger Electron
• An x‐ray is not always emitted as the electrons from outer shells fill in the vacancies
Th i i i i d f d• The excitation energy is instead transferred from the inner electrons to the outer.
C j ti f th l t• Causes ejection of the electron
Auger ElectronAuger Electron
X Ray SpectrumX‐Ray Spectrum
The Results!!!!!
Electron EjectionElectron Ejection
Hilal GencHilal Genc
Th T h i t U Vi t G h'The Technique to Uncover Vincent van Gogh's Patch of Grassf
About 1/3 of Van Gogh's paintings have hiddenAbout 1/3 of Van Gogh s paintings have hidden images
Van Gogh often painted over his older paintings as he had new ideasas he had new ideas
A team of researchers at Delft University ofA team of researchers at Delft University of Technology had discovered in detail the
appearance of one of Van Gogh's former worksappearance of one of Van Gogh s former works which was painted under one of his later
i ti P t h f Gpaintings: Patch of Grass
The team was lead by Joris Dik, and they decided to focus on Patch of Grass because they had known from earlier analysis that there was a portrait painting of a
Dutch woman under the later visible work
The researchers at Delft University of Technology had been able to fathom an idea of the older painting
through several technologies and through the elements found on the paintingp g
They recorded the decimeter scale fluroscence intensity maps that showed a distribution of certain
elements in the paint layers
This indicated that there was actually a painting beneath the Patch of Grass
From there they could visualize van Gogh's y gbrushstrokes and the details of a face
There are two different kinds of mapping techniques
Conventional x ray radiography: the absorption of primary x rays is recorded‐the absorption of primary x rays is recorded‐is an older technique
The traditional radiographic analysis has shown that there is the painting of a head under the Patch of Grass
Traditional x ray radiography looks at the entire material at once
It is sensitive to heavier elementsIt is sensitive to heavier elements
''It can give partial or colorblind view''It can give partial or colorblind view
X ray fluoroscence (XRF) mapping: ‐a newer technique ‐measures the intensity of element specific radiation (energy emitted by atoms while an energetic x ray b h f )beam scans over the surface)
XRF mapping is preferred and was used by Dik and the rest ofXRF mapping is preferred and was used by Dik and the rest of his team
He showed the distribution of the elements, which mostly belonged to the painting at the surface
It helps scientists have a more detailed analysis of the painting
Lead (Pb), Mercury (Hg) and antimony (Sb) were three major elements that were found on the surface of the
painting
Lead appeared to have been spread out throughout the painting
This suggests that Van Gogh had placed a lead based white priming layer over the earlier painting before p g y p g
starting Patch of Grass
The XRF mapping had directly connected the earlier pp g ypainting of the Dutch woman to the elements mercury
and antimony y
"The signals of antimony and mercury were totallyThe signals of antimony and mercury were totally obstructed in the regular conventional X ‐ ray image. We [didn't] see their distribution [before] because theWe [didn t] see their distribution [before] because the X – ray absorption image was totally dominated by the
lead signal" ‐ Diklead signal Dik
Vermillion is a substance with a red pigment containing mercury sulfide
This color was mostly found on the mouth and cheeks of the face, so it would be easier for the researchers to
identify the painting
Antimony was harder and more confusing to find in the paintingp g
It was at first thought by the researchers thatIt was at first thought by the researchers that antimony in the painting was a part of the compound
lead antimonate (Pb Sb O )lead antimonate (Pb2Sb2O7)
Lead antimonate is also known as Naples yellow andLead antimonate is also known as Naples yellow and was used by Van Gogh often during his years in the
NetherlandsNetherlands
Lead was found throughout the paintingLead was found throughout the painting
H l d' di t ib ti th h t th i tiHowever, lead's distribution throughout the painting did not match that of antimony
A method called X ray absorption near end structureA method called X ray absorption near end structure (XANES) was used and is a type of absorption
spectroscopyspectroscopy
Spectroscopy: deals with the analysis of interactionsSpectroscopy: deals with the analysis of interactions between matter and radiation
XANES method with some more analysis confirmed that antimony did belong to the Naples yellowthat antimony did belong to the Naples yellow
Possibility: The pigment has been mixed with lead y p gwhite or zinc white to lighten some parts of the
paintingp g
The Doris‐III syncrotron light source at DuetschesThe Doris III syncrotron light source at Duetsches Elektron‐Syncrotron (DESY) in Hamburg, Germany
was used to examine Van Gogh's workwas used to examine Van Gogh s work
The team collaborators had figured out that theThe team collaborators had figured out that the painting of the Dutch woman was within 17.5 cm x 17 5 cm within a certain area of the newer painting17.5 cm within a certain area of the newer painting
They scanned that area in front of a pencil beam of high intensity x raysg y y
90 000 individual measurements were taken90,000 individual measurements were taken over the 17.5 x 17.5 cm (sq) area
Time of the beam at each pixel was 2s, and the total amount of time to scan took 2 days
“For every pixel scanned, we record the fluorescence spectra to get the full elemental analysis. From this we can deduce which pigments were used and create a three‐dimensional model of the painting. We can then peel off the layers one by one until we get to the layer of interest.”‐ Joris Dik
The covering surface layers will not significantly block the high‐energy fluorescence signals from heavy g gy g yelements in the hidden layers
This way, the distribution of both minor and major components in the painting could be seencomponents in the painting could be seen
Data can be obtained much more quickly by using high intensity x ray beamsg y y
Next, the L mirofluorescence beamline at DORIS‐III, a , ,second genetration syncrotron light source, was usedused
A pencil beam (0.5 mm x 0.5 mm) ofA pencil beam (0.5 mm x 0.5 mm) of quasimonochromatic synchrotron radiation with energy of 38 5 KeV was used to primarily excite theenergy of 38.5 KeV was used to primarily excite the electron
Fluorescence was recorded at each pixel with a high l i di i G dresolution energy dispersive Ge‐ detector
The net peak areas for all the identified elements were determined using the spectra that were processed through the software AXIL6
Elemental distribution images were then reconstructed from the resulting set of peak areas
Those measurements were carried out at beamline C of HASYLAB at DESY.
Energy calibration was performed by transmission measurements of an Sb foil and the use of a high‐
resolution Renishaw optical encoder system mounted on the theta goniometer.g
Goniometer: an insrument used for measuring gsolid angles, such as crystals
These maps were then compared with the features on the surface painting as well as XRF and IRR
imaging
From the elemental distribution maps found from XRF, antimony could be identified as an important
tracer element of the hidden layer
In order to learn about the chemical binding of the Sb, the researchers performed X‐ray absorption , p y p
near edge structure (XANES) measurements at the Sb K‐edge on the most interesting points of theSb K edge on the most interesting points of the
hidden layer.
To identify the pigments of the painting, y p g p g,measurements were done in reference to antimony compounds which are known to have been used ascompounds which are known to have been used as paint pigments when the painting was first finished
These substances are Naples yellow (Pb2Sb2O7), valentinite (Sb O ) and kermesite (Sb S O)valentinite (Sb2O3), and kermesite (Sb2S2O)
For the measurements parts of the mineral grainsFor the measurements, parts of the mineral grains were removed and ground to fine powders
A microscopic sample was taken from the painting in order to study the elements composing it in the upper and lower paint
The paint sample was embedded in epoxy resin
The orientation of the sample in the resin was set up so that the cross section, perpendicular to the original paint surface,the cross section, perpendicular to the original paint surface,
could be studied
The surface of the resin was ground flat with corundum paper and polished with fine diamond pastes up to a final diameter
of 0.25 μm
The objective is to find the elemental components and how they are distributed within the paint layers
Ca K lines and Sb L lines strongly overlap, and software package PyMca was used to fit fluoroscent spectra
Spectra were recorded with a Keymaster Tracer III‐V p yequipped with a rhodium X‐ray tube and a peltier
cooled SiPIN diode detector.
In this way it was possible to position and move the PXRF along the paint surface, in a stable and accurate
way, without ever touching the object.y g j
Because of the limitations of XRR, the facial ,characteristics could not be clearly read, so the face
was not properly visiblep p y
The XRF scan of the painting revealed how someThe XRF scan of the painting revealed how some elements were distributed and this mostly corresponds with the surface paintingcorresponds with the surface painting
Its main elemental components include transition metals such as Mn, Cr, Co, Fe, Cu, Zn, As, and Ba
The zinc that was identified is most probably associated with zinc white (ZnO), a typical pigment
used by Van Gogh in that period
However, they observed a weak overlap with Sb concentrations in the light parts of the nose, ear, and g p , ,collar of the head, strongly suggesting the use of zinc
white in these lighted areasg
In order to examine further the chemical Sb‐compound in the plower portrait, XANES K‐edge measurements were performed
at selected positions on the head
This indicated that valentinite (Sb2O3), a white pigment i t d d i th 1920 b d ibl Sbintroduced in the 1920s can be assumed as a possible Sb
source
Instead, the acquired XANES spectra were rather similar to that of Naples yellow (lead antimonate)p y ( )
Apart from indicating that Sb is present as an antimonate [Sb(+V) valence state], the XANES did not provide additional information on the molecular compound where Sb is present.
B t th tBetween the two paintings, there was a 50 μm thick whitea 50 μm thick white layer. This served as a (secondary) ( y)priming layer for the landscape painting, as shown by the uniform l t l di t ib tilateral distribution of Pb
Van Gogh's palette contained various black and brownVan Gogh's palette contained various black and brown pigments, including earth colors (Fe, Mn), bone black
(C ) d b bl k (C)(Ca), and carbon black (C).
Th l K li fl f h lThe low‐energy K‐line fluorescence of these elements, however, will have been absorbed by the intermediate
l blayer containing Pb
Thus the reconstruction does not include all colorThus, the reconstruction does not include all color components and in particular misses browns and blacks.
These dark colors would improve visualisation of the t l i ti d ld b tt ill t t l thactual painting and could better illustrate a rural, earthy
atmosphere that Van Gogh was expressing
The reconstruction shows approximate and selected l d b d h ld b d dcolor distributions and should not be considered to
show the absolute color of the painting
101 Homework 1 (100922)101 Homework 1 (100922)
1) Why Dik et al undertook this project?2) How did we know that at least 1/3 of van Gogh’s painting are on re used canvas?2) How did we know that at least 1/3 of van Gogh s painting are on re‐used canvas?3) What is synchrotron radiation based X‐ray fluorescence mapping? What makes
this tool unique?4) Find a van Gogh’s painting you like most (show ppt) why?4) Find a van Gogh s painting you like most (show ppt), why?
Submit your answer on using ppt with “lastname 1” as file nameSubmit your answer on using ppt with lastname 1 as file name.
The emission of the innermost electron leaves a vacancy in the inner shell, thus leaving the atom in an unstable condition. As the atom returns to a stable
diti l t f th t h ll fill th i T f i th condition, electrons from the outer shells fill the vacancies. Transferring the electron to the inner shell results in the emission an x-ray whose energy is the difference between the binding energy of the shells. This x-ray, a secondary x-ray or a fluorescent x-ray, is unique for each atom.
e‐
e‐
e‐e‐
ΔE = E3 – E1 = Kβ
K = 1
e‐e‐
L = 2
M = 3e‐ e‐
e‐
e‐ΔE = E2 – E1 = Kα N = 4
e‐
Chemical analysis of the watercolor using surface enhanced Ramanspectroscopy (SERS) shows that the red and yellow pigments usedfor the sky have significantly faded over time. A simulation of theoriginal colors casts a rather different hue onto the scene – instead of ableached out sky, there is a soft orange glow of sunset