Summer 1997

Corollary: The Science Behind Coca Cola Green

As a graduate student in the early 1950s, Carl Clark '45 gained experience in spectrophotometry, a skill that to a brief but memorable sidelight in his young career. One day he met a secretary at Coca Cola Export Corporation, who asked if he would be willing to fix some instruments the company was using. In the process, he learned that RCA had developed for Coca Cola an automatic system for spotting foreign matter (mice, cigarettes, etc.) that had not be removed from returned bottles when they were washed out. The system examined full bottles on the production line by spinning them, stopping them, then passing a beam of light through them. A photocell detected pulses that indicated that an object was rotating in the beverage. The machine rejected bottles with foreign objects and any bottle too dark to permit light to be transmitted. Unfortunately, many of the bottles made in plants in the northern U.S., where iron-rich sand produced glass much darker than the standard light-green Coca Cola bottle, were being kicked out. "I said, 'That's a problem of transmission-I can deal with that,'" Clark says. "I broke up a bunch of bottles and ran the spectra. I used what I learned to build a little machine that had had the S-1 photodetector from the RCA machine and could tell right away if the bottle had enough transmittance to be acceptable."

Coca Cola had assigned the same task to the Southwest Research Laboratory, which built a complicated machine that used trichromatic color imagery. "One day we had a shoot-out," he says. "They handed me a bunch of bottles that had already been checked, and I quickly determined which were good and which were bad. Their team, all in lab coats, put the first bottle in their machine, fiddled and fiddled, and five minutes later reported back, 'We think this one is OK....'" Clark's machine was introduced into the production line. Having begun to study the spectra of Coca Cola bottles, he finished the job. He went through the methodology developed by the International Committee on Illumination for developing a color standard (taught by Dr. Alan Parker in his optics course at WPI) and wrote the specifications for "Coca Cola Green," which became part of the manufacturing specs the company used from that point on.

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Last Modified: Thu June 10 11:52:03 EDT 1999