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Chemistry 151

Chemistry 151. Chemistry and Color (from an elementary school perspective). ACS Outreach. Electromagnetic radiation. Light is a form of energy that travels through space like a wave and is characterized by its wavelength. Electromagnetic radiation.

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Chemistry 151

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  1. Chemistry 151 Chemistry and Color (from an elementary school perspective) ACS Outreach

  2. Electromagnetic radiation • Light is a form of energy that travels through space like a wave and is characterized by its wavelength.

  3. Electromagnetic radiation • Only certain wavelengths of light (visible light) can be detected by the human eye. • “White” light is actually composed of all colors in equal amounts.

  4. Color Perception • Objects appear colored when they reflect light of that color. • Red cone cells in the eye respond, signalling to the brain that the apple is “red”.

  5. Pigments • Pigments are molecules that absorb certain colors of light and reflect the others. • A pigment generally absorbs light that is complementary to the observed color. • Absorbance data can be correlated to the identity of pigment.

  6. Pigments • The absorbance of light can be measured with a spectophotometer.

  7. Pigments • A purple pigment absorbs yellow-green light.

  8. Pigments Food Coloring Data: Color Absorbance Max Yellow 425 nm (absorbs violet) Red 522 nm (absorbs cyan) Blue 610 nm (absorbs orange)

  9. Pigments • Adding magenta, cyan, and yellow pigments in equal proportions leads to black. • Adding magenta, cyan, and yellow pigments in unequal proportions leads to all possible colors of pigments. • Magenta, cyan, and yellow are the primary colors of pigments.

  10. primary colors secondary colors tertiary colors Primary Colors of Pigments • Equally adding adjacent pigments leads to the development of color wheels.

  11. yellow green red cyan blue magenta Complementary colors • Colors opposite each other on color wheels are complementary colors. • Pigments of complementary colors add in equal amounts to give black.

  12. Complementary colors Yellow and blue Magenta and green Red and cyan

  13. 2012: Color Wheels Primary and secondary colors are introduced to show that some colors are made when mixing other colors together. Students make their own color wheels using homemade paint. Teko Mmolowa ’12

  14. Colors in art • Paints are a homogeneous mixture of a pigment, which provides color, and a binder, which cements the pigment to the solid support after drying.

  15. charcoal brown ochre Pigments in nature • Early artists had primarily earth tones in their palettes, many mineral-based.

  16. hematite (Fe2O3 · nH2O) is a source of red, yellow, and brown ochre cinnabar (HgS) is a source of the red pigment vermilion azurite (2 CuCO3 · Cu(OH)2) Mineral-Based (Inorganic) Pigments

  17. Tyrian purple Madder lake (alizarin) Plant & Animal-Based (Organic) Pigments Indigo

  18. Common Sources of Pigments Marigolds Grape Juice Beets Cochineal Beetles Walnut hulls Kool-Aid

  19. CH112: Color Activity • Learning Goals: • Investigate the interaction of dyes with different fabrics. • Identify ionic and polar groups in dyes and fabrics. • Identify the different types of bonding interactions between dyes and fabrics.

  20. The chemistry of fraud detection History of blue pigment use Pigment/Metal Dates in use Azurite/Cu until 1800 Ultramarine/Al until 1828 Prussian Blue/Fe post-1704 Synthetic Ultramarine/Al post-1828 Cerulean Blue/Co, Sn post-1850 Manganese Blue/Mn post-1935

  21. 2008: Art Fraud Activity Last Friday, a priceless masterpiece was stolen from the little-known Waterville Museum of Old Weird Art. The painting was the masterpiece of the great Italian finger painter, Alfredo Fettuccini. However, yesterday the caretaker told police he forgot he had taken the painting home to clean it, and found it in his bedroom the next morning. An original painting by Fettuccini and the painting produced by the caretaker have been confiscated, packaged, and sent to the Colby Chemistry Lab for analysis. Alfredo Fettuccini 1600 - 1650

  22. The case of the missing masterpiece You suspect that the caretaker, Ebenezer Wheezingeezer, stole the real painting and replaced it with a fake. You will investigate the pigments used in the paintings and then look for clues on the paintings themselves. The Waterville Museum of Old Weird Art has granted you special permission to handle these rare paintings. The police are standing by, awaiting your judgment. Ebenezer Wheezingeezer 1950 - ????

  23. The case of the missing masterpiece • The following pigments were characterized: • Pigment from the “Masterpiece” Ebenezer found • Pigment from a modern painting • Pigment found on the floor of the museum • Pigment from a preserved brush of Fettuccini • Pigment stain found on Ebenezer’s overalls • Techniques included absorbance spectroscopy, chemical tests for iron, pH, and fluoresence.

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