1. AA&A spring 20021

2. 2 RGB complements

3. AA&A spring 20023

4. 4 CMY complements

5. AA&A spring 20025 Mixing paints and subtractive filters C-Y pair—only green is transmitted

6. AA&A spring 20026 Mixing paints and subtractive filters Y-M pair—only red is transmitted

7. AA&A spring 20027 Mixing paints and subtractive filters M-C pair—only blue is transmitted

8. AA&A spring 20028 *****Subtractive mixing***** A paint (A) is made using a mixture of two pigments, yellow and blue. The blue transmits light only from 400 nm to 510 nm, while the yellow transmits only from 520 nm to 600 nm. What will be the color of the mixture? A paint (B) is made using a mixture of two pigments, yellow and blue. The blue transmits light only from 420 nm to 540 nm, while the yellow transmits only from 530 nm to 650 nm. What will be the color of the mixture? A paint (C) is made using a mixture of two pigments, yellow and cyan. The blue transmits light only from 420 nm to 560 nm, while the yellow transmit only from 510 nm to 650 nm. What will be the color of the mixture? Which of the three is the brightest? Which of the three is the most saturated? black, green, green, C, B

9. AA&A spring 20029 Mixing paints and subtractive filters M-C pair—only blue is transmittedY-M pair—only red is transmittedC-Y pair—only green is transmitted

10. AA&A spring 200210 Rest of electromagnetic spectrum? Near infra-red (IR)—wavelength > 800 nm Near ultra-violet (UV)—wavelength < 400 nm X-ray—wavelength ~ 0.01-1 nm

11. AA&A spring 200211 Infra-red (IR)—index of refraction Index of refraction n is less in IR than in visible Implies less reflection, less scattering, deeper penetration of light into paint

12. AA&A spring 200212 IR—particle size and wavelength In addition to wavelength dependence of index n What if particle size same or less than wavelength: –New physics –Scattering falls off rapidly with longer wavelength –(blue scattered more strongly than red and IR) Scattering strength wavelength Particle size

13. AA&A spring 200213 Wavelength dependence of scattering What happened to the sky in the IR photo? Blue sky, red sunsets Yellow fog-lights on cars Again, deep penetration of IR into paint layer

14. AA&A spring 200214 IR—particle size and wavelength Particle size same or less than wavelength: –New physics –Scattering falls off rapidly with longer wavelength IR penetrates more deeply into paint than visible Scattering strength wavelength Particle size

15. AA&A spring 200215 IR—selective absorption Brick—reflects more in the red than in the IR Leaves—reflect more in IR than in the red Charcoal absorbs everywhere! (Wednesday) linklink to photos

16. AA&A spring 200216 IR-summary IR light penetrates more deeply into paint layer than visible light: both –Wavelength dependence of index n –Particle size small compared with wavelength –—>Possibility of seeing “what’s underneath” Selective absorption –Different image contrast Details depend critically on variety of factors: –specific pigments –binders –particle sizes

17. AA&A spring 200217 UV—selective reflection Links to flowers and rugsflowersrugs

18. AA&A spring 200218 UV—fluorescence 0 -5.0 -6.5 -2.5 UV absorption Visible emission Examples: recall Friday’s lecture Energy in eV

19. AA&A spring 200219 X-Ray fluorescence 0 -5.0 -6.5 -2.5 X-ray absorption X-ray emission Energy in keV

20. AA&A spring 200220 *****Fluorescence***** Based on the level scheme in the UV-fluorescence slide, what other energies might I expect for fluorescence excited by the 4 eV photon? (Note that it’s possible to get two, or sometimes more, photons out for one photon in!) Based on the level scheme in the X-ray fluorescence slide, what other energies might I expect for fluorescence excited by a high energy (enough to knock any electron out of the atom) x-ray photon? (Note that the photon may knock any one of the electrons out.) 1.5, 2.5, or 4 eV; 1.5, 2.5, or 4 keV

21. AA&A spring 200221 X-rays—spectroscopy Fluorescence—XRF –Another element specific spectroscopy –Excitation of inner shell electrons by X-rays in—X-rays (longer wavelength) out Electron beam in—X-rays out Proton beam in—X-rays out Excitation beam: X-rays, electrons, ions, protons X-ray energy analyzer sample X-rays

22. AA&A spring 200222 XRF in action

23. AA&A spring 200223 X-Ray radiographyradiography Lighter = less exposure

24. AA&A spring 200224 How does it work? X-ray absorption X-ray photo is a shadowgraph X-ray absorption ~ # of electrons = Z H, C, N, O: Z = 1, 6, 7, 8 Ca, Fe: Z = 20, 26 lead (82), titanium (22): could you tell PbO from TiO 2 ? X-ray source guts spine film

25. AA&A spring 200225 IR—UV—X IR—smaller index n, longer wavelength, selective absorption –Penetration reveals deeper material –Modified images UV—selective reflection, fluorescence –Modified images –Enhanced visible intensities –Pigment identification X—fluorescence, Z dependent absorption –XRF spectroscopy –X-radiography