Polarized Light Reveals Detail and Beauty of Ice
Daniel S. Burgess
Using polarized light to reveal the crystallographic structure of a thin cross section of an ice core enables a reconstruction of how the ice formed over the course of a season, with the layers bearing evidence of colder and warmer trends and of precipitation. Beyond its scientific utility, the technique also produces brilliant kaleidoscopic images.
The polarized light images of ice samples are offered as works of art called Frizions. Courtesy of Peter J. Wasilewski.
Ice is a doubly refracting hexagonal crystal with a long axis and three identical, short ones. Its anisotropy causes a crystal to exhibit color under polarized light that depends on its thickness and on its orientation within the sample and with respect to the imaging setup.
The orientation of the long axis in a crystal of lake ice with respect to the surface depends on its growth conditions. Spontaneous nucleation under very cold conditions yields sheets of large crystals with a vertically oriented long axis, while heterogeneous nucleation involving the seeding of cold water by dust or precipitation yields columns of crystals with a horizontally oriented long axis. Ice formed by the accumulation of snow atop lake ice is distinguished by fine crystals.
The polarized images also are aesthetically pleasing, which prompted Peter J. Wasilewski, an astrophysicist at the Laboratory for Extraterrestrial Physics at NASA’s Goddard Space Flight Center in Greenbelt, Md., to offer them as art prints, called Frizions. He collects the images of water frozen in a container, such as a petri dish, using a pair of polarizing filters from Edmund Optics Inc. of Barrington, N.J., and a CoolPix 900 or D100 digital camera from Nikon Corp. of Tokyo, sometimes using 103 magnification.
Wasilewski’s work is being exhibited at the Franklin Institute Science Museum in Philadelphia, and it will appear at Farmingdale State University of New York through the middle of April to accompany a distinguished speakers program called “The Art of Science.” A permanent installation is on display at Goddard Space Flight Center.
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