Van Va Gogh s Hidden Pictures Pictur Koral Modi

Transcription

1 Van Gogh s Hidden Pictures Koral Modi

2 How is chemistry used to analyze art? One example: Raman Spectroscopy When a laser beam hits the surface of a painting, the frequency of the photons in the laser beam change based on what type of material they hit

3 Since each color of paint consists of different elements, the photons change to different frequencies based on the color of the paint they hit, and in this way, scientists t can figure out what color paint was used in the painting. The unique frequency created by different materials is called the Raman Spectrum

4 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 Spectroscopy A similar technique, called X ray fluorescence spectroscopy, was used to discover Van Gogh s hidden pictures. X ray fluorescence spectroscopy penetrates a painting much better than Raman Spectroscopy pyor traditional X ray radiography

5 Van Gogh s background Vincent Van Gogh was born on March 30 th, 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, earthy tones and dull grays

6 The Potato t Eaters, Et Van Gogh, April il1885

7 Van Gogh s early paintings did not sell well. His brother Theo, an art dealer in Paris, told him it was because people were more attracted to the bold Impressionistic style at the time. In March 1866, Van Gogh moved into his brother s apartment in Paris. There, he was immediately attracted to the work of the Impressionists, such as Adolphe Monticelli, Monet, and Degas

8 Van Gogh s Hidden Paintings Inspired dby the Impressionists, i but ttoo destitute to buy new canvases to accommodate his new paintings, Van Gogh was sometimes forced to paint over his old works to save money, creating hidden paintings Experts estimate that Van Gogh painted over 1/3 of his older works. The best known hidden painting is Patch of Grass

9 Patch of Grass, Van Gogh, 1877

10 Hidden Picture behind Patch of Grass

11 X Ray Fluorescence Spectroscopy: Overview Purpose: To non destructively measure the elemental composition of a sample. Applications: i Mining, i Geologic Studies, Ceramics/Glass, Petroleum, Artwork Morgan Dundon

12 Overview Continued Where can these samples be analyzed? Museums Research Centers XRF spectrometer

13 Process 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

14 Process Shells labeled K, L, M, and N. X ray excitation source strikes sample Electron in K shell is ejected! (creates Electron in K shell is ejected! (creates instability)

15 Continued Electron from L or M shell hllfills the vacancy X ray (unique to the element) is emitted. Another vacancy created..electron from M or N now fll fills this A ray emitted once again

16 Vacancies Filled!

17 Auger Electron An x ray is not always emitted as the electrons from outer shells fill in the vacancies The excitation i energy is instead transferred from the inner electrons to the outer. Causes ejection of the electron

18 Auger Electron

19 X Ray Spectrum The Results!!!!!

20 Electron Ejection

21 Hilal Genc

22 The Technique to Uncover Vincent van Gogh's Patch of Grass

23 About 1/3 of Van Gogh's paintings have hidden images Van Gogh often painted over his older paintings as he had new ideas A A team of researchers at Delft University of Technology had discovered in detail the appearance of one of Van Gogh's former works which was painted under one of his later paintings: Pth Patch of Grass

24 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 painting

25 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 brushstrokes and the details of a face

26 There are two different kinds of mapping techniques Conventional x ray radiography: the theabsorptionofprimary of primary x rays isrecorded 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 elements ''It can give partial or colorblind view''

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28 X ray fluoroscence (XRF) mapping: a newer technique measures the intensity of element specific radiation (energy emitted by atoms while an energetic x ray beam scans over the surface) XRF 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

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30 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 starting Patch of Grass

31 The XRF mapping had directly connected the earlier painting of the Dutch woman to the elements mercury and antimony "The signals of antimony and mercury were totally obstructed in the regular conventional X ray image. We [didn't] see their distribution [before] because the X ray absorption image was totally dominated by the lead signal" Dik

32 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 painting

33 It was at first thought by the researchers that antimony in the painting was a part of the compound lead antimonate (Pb 2 Sb 2 O 7 ) Lead antimonate is also known as Naples yellow and was used by Van Gogh often during his years in the Netherlands Lead was found throughout the painting H l d' di t ib ti th h t th i ti However, lead's distribution throughout the painting did not match that of antimony

34 A method called X ray absorption near end structure (XANES) was used and is a type of absorption spectroscopy Spectroscopy: deals with the analysis ofinteractions between matter and radiation XANES method with some more analysis confirmed that antimony did belongto the Naples yellow

35 Possibility: The pg pigment has been mixed with lead white or zinc white to lighten some parts of the painting The Doris IIIsyncrotron syncrotron light sourceat Duetsches Elektron Syncrotron (DESY) in Hamburg, Germany was used to examine Van Gogh's work The 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 painting

36 They scanned that area in front of a pencil beam of high intensity x rays 90, 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

37 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 gy fluorescence signals from heavy elements in the hidden layers This way, the distribution of both minor and major components in thepainting could beseen

38 Data can be obtained much more quickly by using high intensity x ray beams Next, the L mirofluorescence beamline at DORIS III, a second genetration syncrotron light source, was used A pencil beam (0.5 mm x 0.5 mm) of quasimonochromatic synchrotron radiation with energy of 38.5 KeV was used to primarily excite the electron

39 Fluorescence was recorded at each pixel with a high resolution energy dispersive i 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

40 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 highresolution Renishaw optical encoder system mounted on the theta goniometer. Goniometer: an insrument used for measuring solid angles, such as crystals

41 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 near edge structure (XANES) measurements at the Sb K edge on themost interesting points ofthe hidden layer.

42 To identify the pg pigments of the painting, measurements were done in reference to antimony compounds which are known to have been used as paint pigments when the painting was first finished These substances are Naples yellow (Pb 2 Sb 2 O 7 ), valentinite (Sb 2 O 3 ), and kermesite (Sb 2 S 2 O) For themeasurements parts of the mineral grains For the measurements, parts of the mineral grains were removed and ground to fine powders

43 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, 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

44 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 equipped with a rhodium X ray tube and a peltier cooled SiPIN diode detector.

45 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. Because of the limitations of XRR, the facial characteristics could not be clearly read, so the face was not properly p visible The XRF scan of the painting revealed how some elements were distributed and this mostly correspondswith thesurface painting

46 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 collar of the head, strongly suggesting the use of zinc white in these lighted areas

47 In order to examine further the chemical Sb compound in the lower portrait, XANES K edge measurements were performed at selected positions on the head This indicated that valentinite (Sb 2 O 3 ), a white pigment introduced din 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) 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.

48 Bt Between the two paintings, there was a 50 μm thick white layer. This served as a (secondary) priming layer for the landscape painting, as shown by the uniform lt lateral ldistribution ib ti of Pb

49 Van Gogh'spalettecontained various black and brown pigments, including earth colors (Fe, Mn), bone black (Ca), and carbon black (C). The low energy K line fluorescence of these elements, however, will have been absorbed by the intermediate layer containing Pb

50 Thus, thereconstruction does notincludeall color components and in particular misses browns and blacks. These dark colors would improve visualisation of the actual painting and could btt better illustrate t a rural, earthy atmosphere that Van Gogh was expressing The reconstruction shows approximate and selected color distributions and should not be considered dto show the absolute color of the painting

51 101 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? 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? Submit your answer on using ppt with lastname 1 as file name.

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53 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 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 ΔE = E 3 E 1 = K β e K = 1 e L = 2 e e M = 3 e e e ΔE = E 2 E 1 =K α N = 4 e e

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57 Chemical analysis of the watercolor using surface enhanced Raman spectroscopy (SERS) shows that the red and yellow pigments used for the sky have significantly faded over time. A simulation of the original colors casts a rather different hue onto the scene instead of a bleached out sky, there is a soft orange glow of sunset