Reflections
Shines new light on an age-old technology – the Mirror
Background and History

Many of the exhibits in Reflections, on view at the Exploratorium, from June 19-September 20, 2009, are based on a familiar reflecting technology: the mirror. But although the glass in which you see yourself each morning may seem mundane, the mirror’s apparent banality belies its fascinating history.

The first mirror may well have been serendipitous—a surprising reflection in the surface of a still pool or water bowl. But smoothed pieces of obsidian and slate found in Middle Eastern archaeological sites suggest that people were making stone mirrors 6000 or more years ago. Mirrors of copper and other metals began appearing around 4000 BCE with the dawn of metalworking. By 1500 BCE, mirrors of stone and metal were found throughout the Middle East; similar mirrors were being fashioned in China and the Americas.

Glass mirrors were slower to evolve. The art of glassblowing (also a Middle Eastern invention) is thought to be about 2000 years old, and the Romans learned to coat glass with molten metals at around the same time. But a reliable and affordable way to mass-produce flat, metal-coated glass mirrors wasn’t invented until hundreds of years later, in Renaissance Europe.

The sizes and shapes of early mirrors, together with their handles or mounting holes, indicate that at least one use of the mirror has remained unchanged for centuries: Ancient peoples used them for applying makeup or headgear, styling their hair, and examining their own faces. And because they were usually created from highly valued materials, early mirrors tended to be luxury items.

But soon after their invention, it became clear that mirrors were much more than vanity items for the well-to-do. Humans quickly saw tantalizing connections between reflected images and questions of reality and metaphysics. In addition to providing people with views of their own previously unseen faces and emotional expressions, mirrors bounced ephemeral beams of light and provided mysterious glimpses of a subtly altered reality. Mirrors played key roles in the methods of Greek seers, Chinese physicians, South American priests, and European diviners. In paintings, friezes, and ceremonial sites around the world, mirrors were associated with supernatural beings, oracular revelations, and the journeys of the soul.

Mirrors also became important tools for problem-solving and scientific investigation. Egyptian, Greek, and Persian experimenters and astronomers used mirrors to study light and vision for centuries before the Renaissance. A classic legend has Archimedes deploying mirrors to focus the heat of the sun onto enemy ships, essentially creating a giant solar “death ray.” Given the technology of the time, it’s unclear how much fact lies behind this story—but the same idea is at work in today’s solar furnaces, which use arrays of mirrors to generate intense heat by concentrating sunlight on a small point. Such heat can be used directly—to melt metals, for example—or indirectly, by heating water to create steam, drive a turbine, and generate electricity.

The light-concentrating properties of curved mirrors had long been known by the time they were harnessed to study the cosmos. Appearing early in the 17th century, the first telescopes (including Galileo’s model) were refracting scopes, which use lenses to focus light rays and magnify tiny images. Refractors can provide spectacular images, but fine lenses become increasingly impractical with size.

Large mirrors are much easier and cheaper to make than large lenses. Mirror-based reflecting telescopes took longer than refractors to perfect, but Isaac Newton eventually designed a workable model—making today’s giant telescopes possible. (Unlike lenses, the mirrors in a Newtonian reflector also reflect all wavelengths of light at the same angle, so even a simple reflector can create images with all colors in crisp focus. A refracting scope’s lenses must be specially treated to reduce the chromatic aberration resulting from different colors of light focusing at different locations.)

Astronomical tool, optical implement, industrial machine, window on the future—even with this varied history, the most illuminating use of a mirror may still be its power to show us ourselves. Artists like Durer and Rembrandt, famous for their self-portraits, relied on mirrors to capture the subtleties of the human face. Neuroscientist (and Exploratorium Osher Fellow) V.S. Ramachandran uses mirrors to help amputees overcome the confusing sensory information behind “phantom limb” phenomena. Psychologists have used mirrors in research suggesting that humans begin to recognize themselves at around two years of age—and that chimpanzees, orangutans, and perhaps other creatures may have a sense of themselves as individuals. Our centuries-long fascination with mirrors thus reflects the full range of human curiosity, from our innermost identities to the nature of the universe itself.

Find out more on the exhibition at http://www.exploratorium.edu/reflections/

Prepared by Hugh McDonald/Exploratorium