Plastic Pictures

In the language of the laboratory, the thin, transparent material is "thermoplastic"--it softens quickly when heated. It is also "photoconductive"--conducts electricity when exposed to light. Together, these two qualities turn General Electric's newest plastic into a practical contribution to the burgeoning science of instant photography.

G.E.'s new picture-making process is far too complex to compete with Polaroid for the amateur snapshot market. But for some special applications, its lack of negatives or complicated chemical developers is a distinct asset. All that is necessary is to spray the film's photoconductive plastic top with an easily generated positive charge of static electricity. The bottom layer of the film carries an equal, but opposite, negative charge. Those two electric charges, although powerfully attracted to each other, are kept apart by the thin plastic film.

When the shutter is opened and a picture is momentarily focused on the film, the situation suddenly changes. Wherever light hits the film, the plastic it strikes becomes electrically conductive; the positive and negative charges flow together at that point and cancel each other out. Where no light strikes, the opposite charges remain in place, still pulling toward each other like opposite poles of a magnet.

To develop the picture, an electric current is shot through the film for one hundredth of a second. This jolt of juice generates just enough heat to soften the plastic. The electric charges are able to squeeze closer together, dimpling the softened material, which instantly cools and solidifies. The result is a pattern of varying thickness that matches the pattern of light and darkness that made up the original image on the film.

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