Pushing the Rainbow: Frontiers in Color Chemistry; Light and Color in

Chemical Education Today

Meeting Report

Pushing the Rainbow: Frontiers in Color Chemistry; Light and Color in Chemistry Report on Two American Chemical Society Presidential Events by Nancy S. Gettys

On Sunday March 21, 1999, the 217th ACS National Meeting in Anaheim, California sponsored two Presidential Events, “Pushing the Rainbow: Frontiers in Color Chemistry” and “Light and Color in Chemistry”. The events included 10 exceptional and very different speakers who explored various aspects of the importance of light and color in chemistry and chemistry teaching, in other sciences, and in art and human culture. Support for the events was provided by Research Corporation, General Atomics Sciences Education Foundation, Eastman Kodak Company, American Chemical Society, and University of Wisconsin–Madison Materials Research Science and Engineering Center for Nanostructured Materials and Interfaces. Both events were introduced by American Chemical Society President Ed Wasserman. Wasserman noted that color is a critical part of chemistry. A change in color is very often an indication of chemical change. He commented that long before scientists had sophisticated sensors available, people used their senses—sight, smell, touch, and taste—to attempt to understand the world around them. In the modern chemistry laboratory, for safety reasons, only sight (color) is still commonly used. Color is also of vital importance in everyday life, not only in aesthetics and art, but also in the dye industry and in the manufacture of liquid crystal displays and LEDs. Applications of light and color are both practical and aesthetic. Color is easily understood by most people, making it an ideal tool for outreach to the public. Pushing the Rainbow: Frontiers in Color Chemistry The morning seminar, “Pushing the Rainbow: Frontiers in Color Chemistry” was coordinated by Arthur B. Ellis of the University of Wisconsin–Madison. This seminar had an atmosphere far different from the average meeting session at an ACS national meeting. Attendees were greeted at the door and offered a variety of materials to be used during the seminar—a color wheel poster, an envelope of colored films, a sample of photochromic fabric, a liquid crystal thermometer card, a new blue LED, a magnifying glass, JCE Classroom Activity Sheets, and many other items. All were encouraged to register for several door prizes given away throughout the seminar. The atmosphere was set for excitement and learning! Ellis opened the seminar by explaining that the seven invited speakers would address two topics: cutting-edge research and technology; and outreach, including new instructional materials. Information on the symposia, including any

Figure 1. A photochromic T-shirt, available from the Institute for Chemical Education, changes color in direct sunlight.

possible slides used by the speakers during their presentations, is available online at http://mrsec.wisc.edu/edetc/colorsymp.htm.

Coloring the Curriculum John W. Moore, from the Department of Chemistry at the University of Wisconsin–Madison and Editor of the Journal of Chemical Education, spoke on many ways in which color can be incorporated in the chemistry curriculum. He included examples from the Institute for Chemical Education such as SuperScience Connections (1), a resource for teachers in grades K–3. SuperScience Connections integrates science into the regular curriculum. Examples included activities in which K–3 students combine and separate colors and reading assignments involving color. Other resources mentioned from the Institute for Chemical Education included the SPICE program (2), Chem Camps (3), Chemistry and Materials Science Workshop (4), and the ICE photochromic T-shirt shown in Figure 1. Moore described a few of the publications of the Journal of Chemical Education that deal with light and color including Classroom Activity Sheets (5, 6), JCE Software’s Chemistry Comes Alive! CD-ROM series (7, 8), and the JCE Internet dynamic publication, How a Photon Is Created or Absorbed (9). He closed by demonstrating virtual reality software that simulated a spectrophotometer. Not only could the instrument be manipulated using a mouse, but its case could be made transparent (as shown in Figure 2, over) so that students could see its inner workings.

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Meeting Report Literature Cited

Figure 2. This screen from the virtual reality Spectronic 20 shows inner workings of the instrument.

For More Information

1. Super Science Connections: Integrated Activities for K–3 Teachers; Smith, J., Ed.; Institute for Chemical Education; University of Wisconsin–Madison: Madison, WI, 1994. 2. Jacob, A. T.; Dirreen, G. E. In SPICE: The Institute for Chemical Education’s Guide to Student-Presented Interactive Chemistry Experiences; Aristov, N., Ed.; Institute for Chemical Education; University of Wisconsin–Madison: Madison, WI, 1992. 3. Chem Camp is a summer workshop for students in grades 5, 6, 7, and 8. Contact the Institute for Chemical Education for information about the camp or see Chem Camp Handbook: The Institute for Chemical Education’s Guide to the Fun with Chemistry Laboratory Workshops for Middle School Students; Cargille, C., Aristov, N., Huseth, A., Shanks, K., Eds.; Institute for Chemical Education; University of Wisconsin–Madison: Madison, WI, 1992. 4. Materials Science Summer Workshop for high school teachers. Contact the Institute for Chemical Education for information. 5. How Many Colors in Your Computer? Discovering the Rules for Making Colors. J. Chem. Educ. 1998, 75, 312A. 6. CD Light: An Introduction to Spectroscopy. J. Chem. Educ. 1998, 75, 1568A. 7. Jacobsen, J. J.; Moore, J. W. Chemistry Comes Alive!, Vol. 1. J. Chem. Educ. Software 1998, SP18. 8. Jacobsen, J. J.; Moore, J. W. Chemistry Comes Alive!, Vol. 2. J. Chem. Educ. Software 1998, SP 21. 9. JCE Internet, How a Photon Is Created or Absorbed. http:// jchemed.chem.wisc.edu/JCEWWW/Articles/DynaPub/DynaPub.html (accessed April 1999).

Additional information and photographs from Moore’s presentation are available online at http://mrsec.wisc.edu/edetc/colorsymp. htm#Moore_paper. The slides he used can be downloaded in PDF (Adobe Acrobat) format. Information about the Institute for Chemical Education and its publications and workshops are available online at http://ice.chem.wisc.edu/ice/ or contact the Institute for Chemical Education, University of Wisconsin–Madison, Department of Chemistry, 1101 University Avenue, Madison, WI 53706-1396; phone: 800/9915534 (USA) or 608/262-3033. Information about JCE Software and its publications is available online at http://jchemed.chem.wisc.edu/JCESoft/ or contact JCE Software, University of Wisconsin–Madison, Department of Chemistry, 1101 University Avenue, Madison, WI 53706-1396; phone: 800/991-5534 (USA) or 608/262-5153.

An Introduction to the Wonderful World of Color Lawrence D. Woolf, manager of the Applied Physics Group at General Atomics, spoke about color theory. He pointed out that the set of colors considered to be primary colors depends on the application. The most commonly used set of primary colors is red (R), blue (B), and yellow (Y). These are the colors used by artists and taught to school children as primary colors. Unfortunately, the true primary colors for pigments are cyan (C), magenta (M), and yellow (Y).

LIGHT

PRINTING/PAINTING

yellow

YELLOW

(RED & GREEN)

GREEN

RED

magenta

cyan

(RED & BLUE)

(CYAN & YELLOW)

MAGENTA

CYAN

(GREEN & BLUE)

BLUE

Primary Colors of Light: RED, GREEN, BLUE Secondary Colors: cyan, magenta, yellow

Figure 3. The color wheel for additive color (light) emphasizes the primary colors red, blue, and green.

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green

red (YELLOW & MAGENTA)

blue (CYAN & MAGENTA)

Primary Colors of Printing/Painting: CYAN, MAGENTA, YELLOW Secondary Colors: red, green, blue

Figure 4. The color wheel for subtractive color (paints and pigments) emphasizes the primary colors cyan, magenta, and yellow.

Journal of Chemical Education • Vol. 76 No. 6 June 1999 • JChemEd.chem.wisc.edu


These are also called the subtractive primary colors. When mixed, these colors of pigment (such as paint) produce the widest range of colors. For light, as in LEDs and other sources, the mixing of colors is additive. The correct primary colors are red (R), green (G), and blue (B), hence the designation of RGB color for computer monitors and television sets. Combinations of these three colors produce the widest possible range of colors of light. Woolf demonstrated subtractive color combinations very effectively with transparent films that had been distributed to the audience. The source of white light was ambient light, reflected from a white paper envelope. It was simple to observe that overlapping the cyan and yellow films produced green (C + Y = G); the cyan and magenta produced blue (C + M = B); the yellow and magenta produced red (Y + M = R); overlapping all three colors produced black (B) (C + M + Y = B). Experimenting with red, blue, and green transparent, plastic sheets showed that overlap of any two produced black. Woolf then presented a color wheel, different from that usually used by artists, shown in Figures 3 and 4, opposite.

Colors opposite one another are complementary and overlap to produce white light or black pigment. The pairs of complementary colors are yellow and blue, cyan and red, and magenta and green. These are not the complementary pairs usually used in art. Woolf noted that some artists, such as Matisse, used correct complementary colors, thereby producing more striking effects than others who followed the conventional artist’s color wheel. He concluded that additive and subtractive primary colors are easy to demonstrate but are confusing to most people, perhaps due to early incorrect training. For More Information Additional information and photographs from Woolf ’s presentation are available online at http://mrsec.wisc.edu/edetc/colorsymp. htm#Woolf_paper. The slides he used can be downloaded in PDF (Adobe Acrobat) format. More information and instructional materials about color and light, including the colored films demonstrated by Woolf, are available from General Atomics Sciences Education Foundation (online at http://sci_ed_ga.org) or contact Patricia Winter, Educational Materials, Mail Stop 15-113, General Atomics Sciences Education Foundation, 3550 General Atomics Court, San Diego, CA 92121-1194.

Figure 7. This a typical “focal conic” texture observed for smectic phases in which the molecules are arranged into “layers” in addition to being oriented along a particular axis.

Figure 5 (above) and 6 (below). These images are textures of liquid crystals in the nematic phase which have orientational order, but no positional order. Figure 5 is the characteristic “droplet” texture that is observed when the nematic phase begins to form upon cooling from the isotropic (completely disordered liquid) phase. Figure 6 shows the characteristic “threading” observed in nematic textures. The dark threads throughout the colored regions correspond to molecular domains which are aligned with one of the optical polarizers.

Figure 8. This is a texture commonly observed for cholesteric (twisted nematic/chiral nematic) phases. The distinct stripes in the image are associated with the pitch of the helical suprastructure that is formed in this type of phase.


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Additional information and photographs from Park’s presentation are available online at http://mrsec.wisc.edu/edetc/colorsymp. htm#Park_paper. A Web page showing images from her presentation is available at http://mrsec.wisc.edu/edetc/park/index.html. For more information about liquid crystals, see: Collings, P. J. Liquid Crystals: Nature’s Delicate Phase of Matter; Princeton University Press: Princeton, NJ, 1991. Collings, P. J.; Hird, M. An Introduction to Liquid Crystals: Chemistry and Physics; Liquid Crystals Book Series; Taylor & Francis: Bristol, PA, 1997. Chandrasekhar, S. Liquid Crystals, 2nd ed.; Cambridge University Press: New York, 1992. Demus, D.; Richter, L. Textures of Liquid Crystals; Chemie: New York, 1978. Gray, G. W. Smectic Liquid Crystals: Textures and Structures; Heyden & Son: Philadelphia, 1984. Polymers and Liquid Crystal Tutorial. http://abalone.cwru.edu (accessed April 1999). NSF Science and Technology Center ALCOM Home Page. http:// scorpio.kent.edu/ALCOM/ALCOM.html (accessed April 1999).

Phosphors and Organic LEDs Michael J. Sailor of the University of California–San Diego discussed luminescence in nature, phosphorescence, and some technological applications (see Fig. 9). Bioluminescence is observed in several species in nature, among them dinoflagellates found in Mosquito Bay, Puerto Rico. The light is a product of a π aromatic system in luciferin. When it is oxidized, light is produced. He explained that the overall efficiency of the production of light by this method was poor. 740

Figure 9. Copper-doped ZnS powder and some toys containing copper-doped ZnS, illuminated by UV light. The green phosphor in your television set is copper-doped ZnS. Its relatively long excitedstate lifetime accounts for the green glow from your television set after you turn it off.

Sailor went on to describe the use of phosphors in cathode ray tubes and color television screens. Red, blue, and green inorganic phosphors present in the television screen are excited by electrons to produce all the colors needed to display the images. He demonstrated the green phosphor with the assistance of a volunteer from the audience. The phosphor powder was mixed with polyvinyl alcohol, which was then cross-linked with borax solution to form “slime”. The resulting polymer glowed bright green under an ultraviolet lamp. (When asked by a member of the audience, Sailor said he obtained his samples of phosphor powder from Sony and was not aware of a commercial source.) New liquid crystal displays and flat panel screens that use organic polymers have been developed. These polymers have the advantages of being thin, flexible, and very inexpensive. They are not as stable as the phosphors used currently in televisions, but if they are inexpensive enough, disposable TV screens may someday be practical. For More Information Additional information and photographs from Sailor’s presentation are available online at http://mrsec.wisc.edu/edetc/ colorsymp.htm#Sailor_paper. The slides he used can be downloaded in PDF (Adobe Acrobat) format.

photo by George Lisensky

Light and Color in Liquid-Crystalline Materials Lee Y. Park of Williams College talked about liquid crystals, describing how they work and the molecular structures that make the phenomenon possible. She explained that liquid-crystalline materials demonstrate short-range order. The molecules align with order that is intermediate between the random orientations found in liquids and the rigidly ordered structure of solids. In liquid-crystalline materials, there are areas of this short-range order that result in the unusual properties of these materials. One structural feature that results in liquid-crystalline behavior is molecules that have a rigid central region with long, flexible tails (calamitic) on either side. The flexible regions “melt” and move about randomly, while the rigid areas attract one another, ordering the material. A balance of forces results. Another possible structure is a rigid core with flexible tails (discotic). Chemical forces can also result in liquid crystals. A molecule with a polar end and a nonpolar end can form bilayers or micelles with varying degrees of order. The various degrees of order in the arrangement of the molecules produce a series of phases similar to solid phases. The more and less oriented regions react differently with polarized light, producing some very interesting and beautiful colored patterns (see Figures 5–8, previous page). The phase transition from a less to more ordered state can be used in a liquid crystal display. The color of the region depends on energy, temperature, and pressure. This was demonstrated with a liquid crystal postcard thermometer distributed to the audience. For More Information


Meeting Report

Figure 10. LED traffic light.

Exploring Color and Periodic Properties with Light-Emitting Diode Lasers This paper by Arthur B. Ellis, George C. Lisensky, Karen J. Nordell, and S. Michael Condren was presented by Lisensky and Nordell. They gave a brief history of the development of electric light bulbs and LEDs. New LEDs are much more efficient and have a longer life than incandescent light bulbs. LEDs are now being used in automobile brake lights and in traf-




Figure 11. GaN LEDs. Left: at room temperature. Right: in liquid nitrogen. Lowering the temperature decreases the spacing between atoms and increases the energy of the electronic transition.

fic lights (see Figure 10). Replacing standard bulbs with LEDs is not only less expensive but also produces brighter light. A single LED can go out without endangering the public as happens when an incandescent bulb burns out. Lisensky predicted that LED brake lights will be used on all new cars in about three years. The molecular structure for LED material is a tetrahedral arrangement of atoms, like that of carbon atoms in diamond. The identity of the atoms (in combinations that are isoelectronic with carbon) determines the size of the unit cell and the color of the LED. The new, intense blue LEDs contain aluminum, gallium, indium, and phosphorus. Nordell demonstrated both the blue LED and a new tricolored LED that could be used to demonstrate additive-color mixing. Samples of the blue LED were provided to the audience. The audience helped to demonstrate their brilliance by connecting them to 9-volt batteries and holding them up in the darkened room. Lisensky dipped a blue LED in liquid nitrogen to demonstrate the color shift from blue to violet when cooling the material, as shown in Figure 11.

tronic devices. The quantum dot is a possible answer to the need to miniaturize semiconductors. Quantum dots are the clusters of matter larger than a molecule but smaller than usual solid particles. They contain about 1000 atoms, are about 4 nm in diameter, and have different optical properties from their parent materials. Examples demonstrated included a sample of CdS, normally a lemon-yellow, opaque solid. A sample of quantum clusters of CdS was a clear, colorless solution that fluoresced bluegreen light. A second example was PbS—the solid is black, but the quantum clusters formed a clear red solution that fluoresced green light. In these small clusters, quantum effects begin to be important. One-half to one-third of the atoms are on the surface. The chemistries of the “corner” and “side” atoms differ. Shultz focused on optical properties, the band gap in particular, which is larger in the quantum dot than in the corresponding solid. She explained this with a simple model of missing states and a more sophisticated particle-in-a-box model. Quantum dots can be produced by several different procedures, for example: 1.

2.

3.

Polymer Method is used for PbS clusters. It makes large clusters. (For specific directions see Quantum Dots and Modern Electronics, described in For More Information, below). Surfactant Method is used for CdS and makes smaller clusters. The method was adapted from Chandler, R. R.; Bigham, S. R.; Coffer, J. J. Chem. Educ. 1993, 70, A7. (See Quantum Dots and Modern Electronics, described in For More Information, below). Dendrimer Method makes the smallest clusters, ca. 2– 4 nm diameter. See Sooklal, K.; Hanus, L.; Ploehn, H. J.; Murphy, C. J. A Blue-Emitting CdS/Dendrimer Nanocomposite. Adv. Mater. 1998, 10, 1083–1087 for details. Shultz has modified it for PbS and is currently modifying it for gold.

For More Information Additional information and photographs from this presentation are available online at http://mrsec.wisc.edu/edetc/colorsymp. htm#ellis_paper. The slides he used can be downloaded in PDF (Adobe Acrobat) format. See also http://mrsec.wisc.edu/edetc/LED.htm for more detailed information on LEDs.

Quantum Dots: Casting Light on Fundamentals with Cutting-Edge Research Mary Jane Shultz of Tufts University uses practical applications to get students at the introductory level excited about chemistry. She is able to teach such concepts as molecular orbitals, the particle in a box, and the hydrogen atom. Shultz explained that the band gap in semiconductors, composed of elements in Group 4 of the periodic table, depends on the size of the atoms. Outside of Group 4, the band gap increases with increasing electronegativity difference. She noted the trend in miniaturization of electronics and its importance in increasing the speed and reducing the cost of elec-

Figure 12. Clusters of 13 (top left) and 55 (below, right) S2– ions form in the preparation of CdS quantum dots.


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Meeting Report

Figure 13. Color film consists of a layer of gelatin containing silver halide crystals and precursors for magenta, cyan, and yellow dyes on a plastic support. Reprinted with permission from Eastman Kodak Company.

Figure 14. Kodak’s new Academy-Award-winning color film includes innovations in almost all layers of the film. Reprinted with permission from Eastman Kodak Company.

For More Information

agent that reacts with the dyes to produce the complementary color or positive image. A new color motion-picture film developed by Kodak (see Figure 14) recently won a technical Academy Award (Oscar). Special effects can be created using digital video in which the video frames are scanned individually and then edited with a computer. This is an expensive and time consuming process because of the large number of frames that must be scanned (24 frames per second of film!) and the resulting enormous amount of computer storage; about 40 MB per frame are needed to save and edit the high-resolution images. The 1998 film Pleasantville, which appears to have both color and black-and-white images on the same film, was created with digital techniques. The film was originally shot in color. The color film was scanned; color was removed from some areas to produce black-and-white images; and color was enhanced in other areas for added emphasis. Gisser predicted that these advancements would someday be available in consumer photographic equipment and film, but this may take some time due to cost of materials.

Additional information and photographs from Shultz’s presentation are available online at http://mrsec.wisc.edu/edetc/colorsymp. htm#Shultz_paper. The slides she used can be downloaded in PDF (Adobe Acrobat) format. A handout, Quantum Dots and Modern Electronics, can also be downloaded in PDF format. This handout includes detailed procedures for making quantum dots by the Polymer and Surfactants methods described earlier. Materials required for the Dendrimer method are available from Aldrich. Additional references are: Nieman, G. W.; Weertman, J. R.;. Siegel, R. W. J. Mater. Res. 1991, 6, 1012. Mayo, M. J.; Siegel, R. W.; Narayanasamy, A.; Nix, W. D. J. Mater. Res. 1990, 5, 1073. Klots, T. D.; Winter, B. J.; Parks, E. K.; Riley, S. J. J. Chem. Phys. 1990, 92, 2110 and 1991, 95, 8919. An article on quantum dots was recently published in this Journal: Lagally, M. G. Self-Organized Quantum Dots. J. Chem. Educ. 1998, 75, 277.

Color and Light in the Movies Kathleen Gisser of Eastman Kodak Co. described recent developments in color motion-picture film. She suggested that the pot at the end of the rainbow should be silver rather than gold because of the silver chemistry involved in photographic imaging. Gisser estimated that 100,000–250,000 feet of film are shot for a theatrical motion picture and that the resulting movie contains 10,000–12,000 feet of film. Kodak produces several billion feet of film a year—this is a very big business. Gisser explained how film works and described recent advances, including digital technology. Motion picture film consists of layers of solutions in gelatin on a plastic support, as shown in Figure 13. Each layer contains a dye precursor (for magenta, cyan, or yellow) and crystals of silver halide. Light of different color (red, blue, or green) interacts with the dye for its complementary color, producing a negative (or complementary color) image. The film is developed in a high pH solution, containing a developing 742

For More Information Additional information and photographs from Gisser’s presentation are available online at http://mrsec.wisc.edu/edetc/colorsymp. htm#Gisser_paper. Sources of additional information are cited in her bibliography: Hunt, R. W. G. The Reproduction of Colour, 4th ed.; Fountain Press: England, 1987. Billmeyer, F. W., Jr.; Saltzman, M. Principles of Color Technology, 2nd ed.; John Wiley & Sons, Inc.: New York, 1981. James, T. H. Theory of the Photographic Process, 4th ed.; Eastman Kodak Company: Rochester, NY, 1977. Carroll, B. H.; Higgins, G. C.; James, T. H. Introduction to Photographic Theory; John Wiley & Sons, Inc.: New York, 1980. Kennel, G. Digital Film Scanning and Recording: The Technology and Practice. J. SMPTE 1994, 103, 174–181. Silberg, J.; Blair, I.; Heuring, D. Nothing is as Simple as Black and White. Film and Video 1998, 15, 46.


photo by Ari Greenspan

photo by Shira Leibowitz Schmidt


Figure 15. A ritual fringe on a garment worn by observant Jews. One strand is dyed blue.

Light and Color in Chemistry The evening session of the Presidential Event was again introduced by ACS president Ed Wasserman. This session was intended to be less technical than the morning session and focused on the aesthetics of light and color in chemistry.

The Royal Purple and Biblical Blue Roald Hoffmann of Cornell University told a fascinating story of the color blue. It is the story of people doing chemistry long before the development of science. He described and showed slides of ancient works of art, including blue pigments from available, if expensive, mineral sources. However, he explained that these pigments were not useful for dying fabric. Blue dye for fabric was very rare, expensive, and highly sought. The dye was made from three species of snails found in the Mediterranean sea. He explained that the dye comes from a 10–15-mm-long gland in the snails that turns blue or purple when exposed to air and sunlight. Hoffmann estimated that one pound of dyed wool would have cost the equivalent of 300 days’ labor of a baker and that about 9,000 snails were required to produce a gram of the dye. The exact color of dye obtained ranged from light blue to deep purple and appeared to depend on the season and sex of the snail. The purpose this material served to the snail is not known. Manufacture of the dye was a specialty of the ancient Phoenicians, and there is still evidence today of their dye industry and the environmental effects produced by the disposal of snail shells. The blue or purple dye became very significant to the religions and cultures of the Mediterranean area. The “royal purple” version of the dye was so highly valued by the Romans that only certain officials were allowed to wear robes trimmed in purple, and only triumphant generals could wear purple garments. In the Bible, in Numbers, chapter 15, God instructs the Israelites to wear fringes on the corners of their garments with blue cords (see Figure 15). These cords would have been dyed “biblical blue” or tekhelet with the snail dye. Hoffmann described the importance that the blue color came to have in Judaism. He said that the exact color and number of fringes are addressed in great detail in the Talmud, and the

Figure 16. Photograph of Roald Hoffmann and three young Israelis who are reviving the ancient art and science of making the biblical blue (tekhelet).

blue dye played a crucial role in a rebellion described in the Bible in Numbers 16–17. The significance of the color is reflected to this day in the blue star and trim on the Israeli flag. At the same time, there was in use a chemically similar blue dye made from the tropical indigo plant as well as from the woad plant that grew all over Europe. This dye was visually indistinguishable from the royal purple and biblical blue. Counterfeiting royal purple with indigo became a capital offense in Rome, and it was considered a very serious sin among the Jews to use blue fringes dyed with indigo. The chemical structure of the indigo dye was determined in the second half of the 19th century, and processes for its synthesis quickly developed. While indigo from plants is still used today, especially in Japan and Africa, most is made synthetically. According to Hoffmann, two to three grams of indigo are required for a pair of blue jeans, and about one billion pairs of jeans are made annually. It would be impossible to fill even 1% of the demand with snail or plant source dye. The knowledge of how to make the snail dye was lost around 600 A.D. Hoffmann explained that the loss was a great sorrow to the Jewish people, and there have been attempts to relearn the process. One of these attempts actually synthesized not the snail tekhelet but Prussian blue from cuttlefish sepia mixed with iron filings and potash. More recent attempts have had some success in making dye from snails. It has been discovered that in order to make the dye colorfast, it must be reduced to a colorless form, applied to the cloth, and then oxidized by air to return to the blue color. Urine was often used as the reducing agent. Hoffmann asked the audience to consider the act of faith that must have been required to remove the color from this very valuable, highly sought-after dye, and the renewal of faith when the color reappeared. Figure 16 shows Hoffmann working with young Israelis who are reviving the process used to make the dye. He specifically noted that the process they used did not involve urine!


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Meeting Report For More Information For more information about the story of biblical blue, see Old Wine, New Flasks; Reflections on Science and Jewish Tradition by Roald Hoffmann and Shira Leibowitz Schmidt, published in 1997 by W. H. Freeman (New York). Roald Hoffmann is also the author of these books about science: Hoffmann, R.; Torrence, V. Chemistry Imagined; Smithsonian Institution Press: Washington, DC, 1993. Hoffmann, R. The Same and Not the Same; Columbia University Press: New York, 1995. An online resource located by the Journal staff may be of interest to anyone who would like to learn more about the continued importance of biblical blue to the Jewish people. See Bluethread at http:// www.exo.net/bluethread/index.html and http://www.exo.net/bluethread/ tzitzit.htm (accessed April, 1999).

Quest for Color in Photography John P. Schaefer is president of Research Corporation (http://www.rescorp.org/), a foundation for the advancement of science. An outstanding amateur photographer himself, he presented a brief history of photography that included many interesting and beautiful examples of early photographs. The two images shown here are of the first true photograph (Figure 17) and the first humans photographed—note the man having his shoe shined near the lower left corner of the photograph by Daguerre (Figure 18). Schaefer explained that photography was developed during the Industrial Revolution, at a time when people were building machines to do the work of men. The motivation was to create a machine that could draw. The idea of a camera and lens was not new. Since the time of Aristotle, people had focused images through a pinhole. In order to capture the focused image, it had to be traced or sketched by hand.

Figure 17. Oriel Window, Lacock Abbey, William Henry Fox Talbot, 1835.

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Some degree of artistic talent was necessary to get good results. Louis Jacques Mande Daguerre was a painter in Paris in the early 1800s. He invented a Diorama, a series of huge wallsized paintings on a lazy-Susan that rotated around the audience in the center. The Diorama was extremely popular with the public, but when the theater burned down, Daguerre began to search for a way to recreate the images without having to paint them again. His method was based on the darkening of silver (silver ion reduced to silver metal) when exposed to light. Through much trial and error, he was able to produce visible images by developing the exposed silver over hot mercury. Daguerreotype images became very popular and, for the most part, eliminated the practice of painting “miniatures” that had been the usual method for obtaining pictures of people. The major problem for the public was that the images were black and white. This was solved by painting the black-and-white images in color by hand. (Schaefer noted that the practice of coloring black-and-white photographs has recently experienced a resurgence.) The major problem of the process was the use of mercury. The Daguerreotype process was only practiced for 10–15 years. William Henry Fox Talbot, an Englishman, developed a more promising photographic process by experimenting with paper soaked in silver nitrate solution. His images were “negatives” from which “positive” images could be printed. A seeming disadvantage—that the images produced were backwards or mirror images of the object photographed— turned out to be popular with the public; they could see themselves in photographs as they were accustomed to seeing themselves in a mirror. Many advances followed rapidly, including the use of gallic acid as a developing agent, sodium thiosulfate in dissolving the silver salt, the albumen (egg white) process, the collodion process, and the use of gelatin to contain light-sensitive materials on a photographic plate. Photography became practical for the common person, and the words photograph, snapshot, negative, and positive became commonly used.

Figure 18. View of the Boulevard du Temple, L. J. M. Daguerre, 1839.



Several different attempts were made to produce color images, including the cyanotype first introduced by John Herschel. It used paper coated with Fe(CN)63– solution to produce a blue-and-white image. Anna Atkins used this process to create stunning, detailed images. Color photography finally became practical in the 1930s with the development of Kodachrome film. Schaefer asked the audience to consider how profoundly photography has affected our lives. Rather than diaries, most people keep scrap books or photograph albums to record their memories. Photography is important personally and as an art form, but it is also important to society. Photographs of war have changed our outlook; images of immigrants and child workers have led to legislative reforms; images of natural phenomena and beautiful landscapes led to the establishment of our national parks. Newspapers, books, and advertisements have all been irrevocably changed by the use of photographs. For More Information For more information about the history of photography, see The Keepers of Light: A History and Working Guide to Early Photographic Processes by William Crawford, published in 1980 by Morgan & Morgan, Inc (Dobbs Ferry, NY). Schaefer is the author of two books on photography: The Ansel Adams Guide: Basic Techniques of Photography (revised 1999), Little Brown & Company: Boston and The Ansel Adams Guide: Basic Techniques of Photography, Volume 2, 1998, Little Brown & Company: Boston. Additional related references and a student activity centered around a pinhole camera are provided in this issue, see pp 736A–736B.

Color of Chemistry: A Photographer’s Perspective If an ordinary picture is worth a thousand words, a photograph by Felice Frankel must be worth at least a million. Felice Frankel is Artist-in-Residence in Science and Technology at the Edgerton Center and a research scientist in electrical engineering and computer science at MIT. She opened her presentation by saying she would not tell the audience how to take pictures but would tell us a little about how she does it. She proceeded to show and talk about a series of stunning images of science, explaining how minor changes in lighting and color can make important differences in the aesthetic appeal of an image as well as in the information it conveys (see Figures 19 and 20). Frankel explained that she had been a landscape photographer for many years and began taking photographs of science experiments in the laboratory of George Whitesides at Harvard University. She showed some of her landscape photographs and explained how the colors and her choice of palette differed from the colors in science. She closed her talk by encouraging us to be more aware of the color and light around us and to realize the importance of color and light in seeing and presenting science to others. Felice Frankel has received grants from the Guggenheim Foundation, the National Endowment for the Arts, and the Graham Foundation. In 1991 she was a Loeb Fellow at Harvard University. You can see more of her work online, in books, on the cover and inside pages of science journals, and in traveling exhibits:

I photographed the square drops of colored water on the right after the researchers and I decided we could improve on their rendition above. One aspect of the research was to demonstrate microcontact printing, creating patterns with hydrophobic “lines” that define hydrophilic areas on a self-assembled monolayer (SAM). My intent was to add an aesthetic component and to reinforce the idea that the drops (about 4-mm on one side) do, in fact, maintain their integrity and do not leak into each other. The image appeared on the cover of Science . (The art department at Science refers to it as the Chiclet cover.) - Felice Frankel

Figure 19. Frankel’s photograph appeared on the cover of Science, 4 September 1992, Vol. 257, pp 1317–1448. It illustrated “Manipulation of the Wettability of Surfaces on the 0.1- to 1-Macrometer Scale through Micromachining and Molecular Self-Assembly” by Nicholas L. Abbott, John P. Folkers, and George M. Whitesides, pp 1380–1381. Photo by Felice Frankel, copyright © 1992.


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Online: http://web.mit.edu/edgerton/felice/felice.html and http://web.mit.edu/feliceF/www/aps1.html. Books: On the Surface of Things, Chronicle Books, 1997, with George M. Whitesides (Harvard University chemist). Modern Landscape Architecture: Redefining the Garden, Abbeville Press, Inc., 1991, with Jory Johnson. Journals: Includes recent issues of Nature, Science, Journal of Physical Chemistry, Langmuir, Cellular Biology, and the Journal of Chemical Education. Exhibitions: Envisioning Physics at the Fernbank Museum, Atlanta, Georgia, March 21–October 1, 1999. After October 1, the exhibit will be traveling.

Felice Frankel is now working on a project for the National Science Foundation called Envisioning Science and Engineering. The effort will produce a guidebook for students and researchers that includes a visual vocabulary of science. Recently she has discussed her philosophy in Science, “Envisioning Science, A Personal Perspective”, June 12, 1998. Notes The figure captions were provided by Felice Frankel. They not only explain what is shown but also describe her approach to and feelings about the photographs. Felice Frankel’s photograph of blue and green squares of water, included in On the Surface of Things (reproduced here, see Figure 19), inspired the development of the mini-activity “Circles and Squares”, published in JCE Classroom Activity #6, On the Surface: Mini-Activities Exploring Surface Phenomena. J. Chem. Educ. 1998, 75, 176A. Jerrold Jacobsen’s color photographs of a checkerboard of water squares

produced using this procedure were included in the table of contents (page 133) of the February 1998 issue of the Journal.

Conclusions The ACS Presidential Events, “Pushing the Rainbow: Frontiers in Color Chemistry” and “Light and Color in Chemistry”, made for a very memorable day at the ACS National Meeting. Many audience members sought out the Journal of Chemical Eduction booth in the exhibition hall to ask for more information about JCE and ICE materials cited in the morning session. Color and light are such an integral part of how we view the world and receive information about the world that they are easily taken for granted. We would all be living very different lives if photographs, movies, television, computer screens, and traffic lights did not exist. The presentations showed not only how vital color, light, and the technology surrounding them are to our lives, but how we can use these familiar items and ideas to provide more interesting and accessible lessons for chemistry students. I thank the speakers for their help in preparing this report. Their assistance in providing the beautiful figures in the report and on the cover of the issue is especially appreciated. I would also like to thank Journal Associate Editors Mary Saecker and Elizabeth Moore for their support and assistance. Nancy S. Gettys is an assistant editor of the Journal. She attended these Presidential Symposia as our reporter.

My first attempt, on the left, photographing these microstructures (about 3-mm wide) was to take a silhouette of the samples using transmitted light with my stereomicroscope. The better image, on the right, taken with reflected light, shows both the intricacies of the patterns and that the structures are, in fact, three dimensional. This image also appeared on the cover of Science . (The art department at Science refers to this one as the “earring” cover.) - Felice Frankel

Figure 20. The photograph on the right appeared on the cover of Science, 26 June 1998, Vol. 280, pp 2013–2176. It illustrated “Design and Fabrication of Topologically Complex, Three-Dimensional Microstructures” by Rebecca J. Jackman, Scott T. Brittain, Allan Adams, Mara G. Prentiss, and George M. Whitesides, pp 2089–2091. Both photos by Felice Frankel, copyright © 1998.

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