RGB complements

2. RGB complements

3. CMY complements

4. Mixing paints and subtractive filters C-Y pair—only green is transmitted

5. Mixing paints and subtractive filters Y-M pair—only red is transmitted

6. Mixing paints and subtractive filters M-C pair—only blue is transmitted

7. *****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

8. 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

9. 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

10. IR—particle size and wavelength Scattering strength wavelength Particle size • 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)

11. 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

12. 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) link to photos

13. 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

14. UV—selective reflection Links to flowers and rugs

15. UV—fluorescence 0 -2.5 -5.0 -6.5 UV absorption Visible emission Energy in eV Examples: recall Friday’s lecture

16. X-Ray fluorescence 0 -2.5 -5.0 X-ray emission -6.5 X-ray absorption Energy in keV

17. *****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

18. X-rays—spectroscopy sample Excitation beam: X-rays, electrons, ions, protons • 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 X-ray energy analyzer X-rays

19. XRF in action

20. X-Ray radiography Lighter = less exposure

21. How does it work? X-ray absorption guts X-ray source spine • 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 TiO2? film

22. 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