The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion Using 21st century spectroscopic tools with 20th century theory to understand the color of 19th century glass from Bangkok’s Temple of the Emerald Buddha Bruce Ravel1, Larry Carr2, Christophe Hauzenberger3, Wantana Klysubun4 1NIST & NSLS Beamline X23A2 2BNL, Photon Sciences 3Karl-Franzens-University Graz, Austria 4Synchrotron Light Research Institute, Thailand ASEAN Conference on X-ray Absorption Spectroscopy July 12-13, 2013 Spectroscopy on antique Thai glass 1 / 31

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion The gang Dr. Wantana Klysubun Synchrotron Light Research Instutute Nakhon Ratchasima, Thailand Dr. G. Lawrence Carr BNL, Photon Sciences Mag. Dr. Christoph A. Hauzenberger Karl Franzens University Graz, Austria Spectroscopy on antique Thai glass 2 / 31

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion The Grand Palace This amazing place is Bangkok’s Grand Palace, the residence of Thai royal family. The Palace grounds house an important Buddhist site, the Temple of the Emerald Buddha (Wat Phra Kaew). Spectroscopy on antique Thai glass 3 / 31 This image is from Wikimedia Commons

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion The Emerald Buddha The Temple houses a small statue of the Buddha carved from green stone.∗ The story goes that it was carved in the 1st century CE in Patna, India. Over two millenia, it took a complex path driven by Buddhist evangelism, war, and natural disaster from India to Sri Lanka, Cambodia, Lanna (now in northern Thailand), Laos, and finally to the Thai capital, then called Rattanakosin (“Keeping place of the Emerald Buddha”), in 1784 during the reign of King Rama I. Today, the statue and its temple are both a tourist attractions and a sacred Buddhist temple. Spectroscopy on antique Thai glass 4 / 31 This image is from Wikimedia Commons ∗jadeite (NaAlSi2O6)

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion The glass mosaic decorations Following construction of the Temple in the late 18th century, the exterior was renovated and decorated with innovative, mirrored, glass mosaics during the 1830s (under King Rama III). The glass was produced at royally sponsored glass workshops in Bangkok. Here we see a pillar on the rear side of the Temple which is still decorated with the original glass mosaic. Spectroscopy on antique Thai glass 5 / 31 This image is by me.

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion The glass mosaic decorations Here is a closeup of the mosaic on that column. Spectroscopy on antique Thai glass 6 / 31 This image is by me.

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion The glass mosaic decorations Here is a restored mosaic using modern, commercial glass. The modern glass is quite different visually – brighter, more reflective. Kind of gaudy, in fact. Spectroscopy on antique Thai glass 6 / 31 This image is by me.

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion The red glass sample Wantana was asked to explore the prospect of recreating the glass with the original formulations for use in future renovations. Let’s do chemical analysis and some spectroscopy! KMHR1 from pillar shown earlier KMSR2 from elsewhere in the temple complex The dark bits are oxidized Sn/Pb alloy used for mirroring Spectroscopy on antique Thai glass 7 / 31

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion Chemical composition: major elements EDX-WDX SEM [wt.%, as oxides] KMHR1 KMSR2 SiO2 37.99(9) 37.59(77) TiO2 < 0.15 < 0.15 Al2 O3 1.41(9) 1.20(13) Fe2 O3 0.37(5) 0.31(4) MnO < 0.15 < 0.15 MgO 0.53(12) 0.56(11) PbO 46.33(103) 51.77(124) CaO 0.94(4) 0.90(8) Na2 O 3.86(5) 3.86(14) K2 O 0.78(1) 0.81(3) Sum 92.20(103) 97.01(131) This glass is heavily leaded – consistent with a refractive index of ∼ 1.65 Spectroscopy on antique Thai glass 8 / 31

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion Chemical composition: minor elements LA-ICP-MS [mg/kg] KMHR1 KMSR2 Ti 212(5) 182(11) Mn 416(8) 309(19) Cu 2204(36) 1883(58) Zn 82(2) 78(4) As 3234(35) 3616(50) Rb 56(2) 50(2) Sr 21(1) 18(1) Zr 20(1) 16(1) Ag 14(1) 13(1) Sn 77(3) 59(3) Sb 60(1) 56(3) Ba 91(1) 82(6) Au 45(1) 49(2) Several of these elements are important to our story: 1 Cu and As are relevant to the optical properties. 2 Sn and Sb (and possibly As) play a role in the redox environment of the glass melt. 3 Au is the central topic of this talk. 4 The mountain of As plays a big role in the XAS measurements. Spectroscopy on antique Thai glass 9 / 31

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion NSLS Beamline X23A2 We began our X-ray measurements at my beamline High energy XRF (12 keV and >29 keV) Au K edge XAS Spectroscopy on antique Thai glass 10 / 31 Photo courtesy Jasen Vita, Sarah Lawrence College, and his iPhone.

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion XRF spectrum These glasses are filled with common transition metals – Mn, Fe, Cu – as well as a substantial amount of As. Intriguingly, there is a bit of gold in these glasses. As Kα: 10543 eV Au Lα: 9713 eV Spectroscopy on antique Thai glass 11 / 31

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion What’s the deal with gold? Here is a famous, 4th century CE, Roman artifact from the British Museum: The Lycurgus Cup. This is the most famous, ancient example of “struck-gold” or “ruby-gold” glass. The red color is caused by nanoscale colloidal gold finely dispersed throughout the glass matrix. Modern recreations of ruby-gold glass involve control of the redox potential in the melt by addition of SnO2 . Done correctly, this reduces gold salt to colloidal, zero-valent gold. The punch line of the story The 19th century Thai glass craftsmen were nanoengineers! Spectroscopy on antique Thai glass 12 / 31 F.E. Wagner, Nature 407 (2000) 691-692. DOI: 10.1038/35037661

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion Tin and antimony Both tin and antimony are present in the glass. Spectroscopy on antique Thai glass 13 / 31

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion Reference measurement Reference foil Sample Four-channel ion chamber Slit assembly Incident beam Ion chamber Fluorescence detector At X23A2 the angular stability of the mono is poor, so a good reference measurement is essential. The glass, however, is too thick to allow passage of beam, even at 12 keV. My solution was to use a 20 mm wide beam and a special ionization chamber for measuring different regions of the swath independently. Spectroscopy on antique Thai glass 14 / 31 B. Ravel et al., J. Synchrotron Rad. (2010). 17, 380-385 DOI: 10.1107/S0909049510006230

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion Reference measurement Reference foil Sample Four-channel ion chamber Slit assembly Incident beam Ion chamber Fluorescence detector At X23A2 the angular stability of the mono is poor, so a good reference measurement is essential. The glass, however, is too thick to allow passage of beam, even at 12 keV. My solution was to use a 20 mm wide beam and a special ionization chamber for measuring different regions of the swath independently. Spectroscopy on antique Thai glass 14 / 31 B. Ravel et al., J. Synchrotron Rad. (2010). 17, 380-385 DOI: 10.1107/S0909049510006230

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion Reference measurement Reference foil Sample Four-channel ion chamber Slit assembly Incident beam Ion chamber Fluorescence detector At X23A2 the angular stability of the mono is poor, so a good reference measurement is essential. The glass, however, is too thick to allow passage of beam, even at 12 keV. My solution was to use a 20 mm wide beam and a special ionization chamber for measuring different regions of the swath independently. Spectroscopy on antique Thai glass 14 / 31 B. Ravel et al., J. Synchrotron Rad. (2010). 17, 380-385 DOI: 10.1107/S0909049510006230

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion Au K-edge XANES With the discriminator window set around the Au Lα peak, we measure this XANES spectrum. Purple line: Au LIII edge energy at 11919 eV. Red line: As K-edge energy at 11867 eV. Energy (eV) Spectroscopy on antique Thai glass 15 / 31

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion Au K-edge XANES Here we compare the “Au” data with a properly measured As K-edge spectrum from the same sample. It looks much the same, but with some excess spectral weight above the Au K-edge energy. Energy (eV) Spectroscopy on antique Thai glass 15 / 31

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion Au K-edge XANES So, we subtract the properly measured As spectrum from the “Au” data, resulting in this difference spectrum. These we will treat in the normal way, using the indicated pre- and post-edge lines for normalization. Energy (eV) Spectroscopy on antique Thai glass 15 / 31

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion Au K-edge XANES Finally, we see the normalized difference spectrum plotted along with transmission XANES from an Au foil. Voil´ a! Metallic gold is clearly present in these glasses. So, why is it red? This is proof that the gold in the red Thai glass is in the metallic form. The XAS does not explain the color. Spectroscopy on antique Thai glass 15 / 31

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion What about the copper? Cuprite, CuO2 , is a brilliant red mineral. Perhaps the red color in the Thai glass comes from Cu1+ ions dispersed in the glass. Spectroscopy on antique Thai glass 16 / 31 This image is from Wikimedia Commons.

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion Copper XANES Our XANES data demonstrate that the Cu is Cu1+ in the glass In cuprite, the red color is due∗ to an absorption process which transfers charge from the O2− ion to the Cu1+ ion. However, in glass, Cu has a filled d band, so there is no available transition. KMHCL2 is a piece of clear glass of the same vintage. Cu is not the colorant. Spectroscopy on antique Thai glass 17 / 31 ∗See The Physics and Chemistry of Color by Kurt Nassau. These data measured at SLRI BL8 − →

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion A bit of history James Clerk Maxwell Garnett (b. 1880) was a junior research fellow at Trinity College, Cambridge when, in 1904, he authored a seminal paper explaining coloration in metals and metal glasses. After a brief career as a mathematical physicist, he became an academic administrator, then lead Britain’s League of Nations Union. Britain along with Thailand (under King Rama VI) were among the founding members of the LN. Photograph of J.C.M. Garnett in the National Portrait Gallery (London) Spectroscopy on antique Thai glass 18 / 31

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion Garnett’s seminal paper “Colours in Metal Glasses and in Metallic Films”, Philosophical Transactions of the Royal Society of London, 203 (1904), p. 385. This journal begun publication in 1665. Isaac Newton published “New Theory about Light and Colours” in 1672. Volume 203 also included an article on acoustics by Lord Rayleigh, the same Lord Rayleigh for whom elastic scattering of photons is named. Spectroscopy on antique Thai glass 19 / 31

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion For decades his work languished... ... then along came nanotechnology and the ability to resolve objects on the scale of 10s of nanometers. Spectroscopy on antique Thai glass 20 / 31

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion NSLS Beamline U10B Use the synchrotron optical, near IR, and near UV spectrum Bruker FTIR spectrometer with CaF2 vis/UV beamsplitter Si and GaP photodiode detectors Transmission spectroscopy at near-normal incidence Analyze as absorbance A = -log(Transmission) Spectroscopy on antique Thai glass 21 / 31 Photo from the U10B webpage

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion Garnett theory for optical properties of heterogeneous materials E applied p = α·E When an electric field is applied to an atom of polarizability α, a dipole is created. Spectroscopy on antique Thai glass 22 / 31

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion Garnett theory, cont. E applied An electric field applied to a solid results in an array of dipoles. Macroscopic optical response given by the dielectric function ε(ω) ≡ ε (ω) + iε (ω) and the refractive index n = e1/2 E applied E local The local electric field at any point in the solid includes the induced fields of the surrounding dipoles. Spectroscopy on antique Thai glass 23 / 31

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion Garnett theory, cont. E applied E local The Clausius-Mossotti relation connects macroscopic dielectric response ε with the polarizability α of the individual atomic (or molecular) components. ε−1 ε+2 = 4π 3 Nα Spectroscopy on antique Thai glass 24 / 31

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion Garnett theory, cont. E applied E local ε particle Generalized form for polarizable components embedded in an existing dielectric εb . εeff−εb εeff+εb = 4π 3 Nα Spectroscopy on antique Thai glass 25 / 31

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion Garnett theory, cont. Let polarizable entities be spherical inclusions of radius a 1 and having dielectric response εinc inside host material of εhost . α = εinc −εhost εinc +εhost ·a3 Substitute and solve for εeff . This is Garnett’s dielectric response for a composite. εeff = εhost + εinc 3f (εinc −εhost ) (1−f )(εinc −εhost )+3εhost Assume that the inclusion is dilute, f 1, and solve for the absorption coefficient: A(ω) =2ωc−1 Im ε(ω) = 18f ω2ε1.5 host c2 εinc (εinc + 2εhost )2 + (εinc )2 There is a resonance when εinc = −2εhost Spectroscopy on antique Thai glass 26 / 31

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion Dielectric response for gold Glass with n ≈ 1.5 has εglass ≈ 2.25 So gold in glass has a resonance when εAu ≈ −4.5. That happens at about 2.3 eV. Spectroscopy on antique Thai glass 27 / 31 P.B. Johnson and R.W. Christy, Phys. Rev. B 6, 4370-4379 (1972) DOI: 10.1103/PhysRevB.6.4370

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion Optical spectroscopy 0 0.5 1 1.5 2 2.5 1 1.5 2 2.5 3 3.5 1033 774 619 516 442 387 Optical density (a.u.) Energy (eV) Wavelength (nm) GaP Si Garnett Infrared Ultraviolet The red and blue traces show the absorption of light by the glass. The purple trace is the predicted absorption by 30 nm Au spheres in glass using J.C.M. Garnett’s theory. Other elements (Fe and As) cause strong absorption in the ultraviolet. Yellow, green, blue, and violet are absorbed. Red transmits. Green light is absorbed due to the gold. Gold → red, no gold → green Spectroscopy on antique Thai glass 28 / 31

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion The proof of the pudding... Wantana is working on recreating the antique glass This is glass she made with the chemical composition of the original red glass, but without gold. This glass has the chemical composition of antique clear glass, but with 0.1 wt% AuCl3 and 0.2 wt% Sb2 O3 . The color is not quite right, but close! Spectroscopy on antique Thai glass 29 / 31

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion We’re making progress! Yellow and clear Published∗ Red Ready to submit† Blue and green Forthcoming Learning how to blow and flatten the glass, then cut it into tiles will be another story entirely! Spectroscopy on antique Thai glass 30 / 31 ∗W. Klysubun, et al. Applied Physics A 11:3 (2013), pp 775-782, DOI: 10.1007/s00339-013-7657-8 †will be submitted to Spectrochimica Acta

The Temple Samples X-ray measurements XAS Optical spectroscopy Conclusion Questions for an art historian 1 What is the source of the lead? Perhaps galena (PbS). Knowing this would help understand the origin of the various impurities. 2 How was the reductant introduced? Was Sn or Sb introduced directly? Or as an impurity of some other constituent? 3 What is the source of the gold? AuCl3 is unlikely for the time period. Perhaps chloroauric acid (HAuCl4 ), the product of dissolving gold in aqua regia, was used. 4 What blowing and cutting techniques were used? 5 How did the Thai craftsmen know about the ruby-gold technique? Via contact with Europe (where it was rediscovered in the late 17th century)? Via contact with China? Independent discovery? Spectroscopy on antique Thai glass 31 / 31