Contrary to appearances, the images above are not of a stained-glass window. They show a simple pane of glass layered with transparent adhesive tape of various thicknesses and orientations. The colors emerge only when the glass is illuminated by linearly polarized white light and viewed through a linear polarizer, in this case a pair of polarized sunglasses.
The trick to creating such art is pairing birefringent materials with polarization filtering. The index of refraction for certain materials depends on the light’s polarization relative to specific axes of the material. As a result, the light’s polarization can change as the light travels through the material, a change that depends on the initial polarization and wavelength. For a given angle of a linear polarizer—the sunglasses—only light with a polarization component in that direction will show up, so the colors change with the angle. For example, the circular patch at the center of the glass artwork above is green when the sunglasses are set to transmit vertical light (top image), but pink when the sunglasses have been rotated 90° (bottom image).
Aaron Slepkov, a physics professor at Trent University in Canada, created the artwork at the beginning of the article and above and a series of other pieces. In a recent American Journal of Physics article, he detailed the science and sometimes counterintuitive methods behind art that gains its coloring from birefringent materials. The technique was introduced in 1967 by artist Austine Wood Comarow, who named it Polage—a portmanteau of polarization and collage. An example of her work, a Polage mural housed at the Boston Museum of Science, is shown below. Its hexagons (background) contain hidden patterns that are revealed when polarizers in the room (foreground) are set at specific angles.
The sorts of everyday materials amenable to Polage make it an accessible classroom demonstration or rainy-day activity, even for those who, like me, aren’t artistically talented. Following the lead of Slepkov, I used a white computer screen as a source of linearly polarized light and a pair of polarized sunglasses as my filter. For my birefringent materials, I employed folded plastic wrap (top left, below) and layers of Scotch tape (bottom left). The best results, however, came not from my own design but from a ridged plastic cup (right). Local stress is frozen into the plastic during manufacturing and creates varying birefringence and a beautiful rainbow pattern.
