HOW COME? Why we see art in ice

How come we sometimes see miniature, flowerlike shapes inside ice cubes? asks a reader.

If you've ever looked at an ice cube under a bright light, you may have noticed them: an array of tiny, decorative figures, a hidden pattern in the warp and weave of the ice. John Tyndall noticed them, too, more than a century ago. Today, the icy figures bear his name.

John Tyndall was a 19th century physicist, born in Ireland in 1820. Among his many areas of interest -- from magnetism to the Earth's atmosphere -- Tyndall was also fascinated by glaciers and ice, keeping journals of his many climbing expeditions in the snowy Alps.

In one experiment, Tyndall cut a cube from a chunk of lake ice, then studied it in beams of sunlight. As sunlight penetrated the cube from different directions, Tyndall observed "bright bubbles" forming inside the ice.

According to Cleveland State University physicist Jearl Walker, any chunk of ice contains many six-sided crystalline plates. Each crystal usually forms around impurities in the water (whether from a lake or the kitchen faucet). Looking at his chunk of lake ice at different angles through a magnifying lens, Tyndall saw odd designs in the ice. When he viewed areas perpendicular to crystalline layers in the ice, Tyndall saw long cracks, with feather-like spurs.

But when he looked parallel to the frozen layers, Tyndall said, "a very beautiful appearance revealed itself." The illuminated ice, he discovered, was "filled with little flower-shaped figures." Each figure had six tiny petals. The petals, he noted, were composed of liquid water, encased in ice. Each "flower" had a brilliantly shining center.

These "liquid flowers," as Tyndall called them, are now known as Tyndall figures. The figures, as Tyndall noted, come in other shapes, too, from ferns to hexagons.

What causes the mysterious figures to form? According to Walker, Tyndall figures are created by melting in the interior of ice. Infrared light (from sunlight or a lamp) easily penetrates an ice cube. But instead of being absorbed evenly throughout the cube, its heating energy is absorbed mainly at the cube's "defects" -- places in the icy structure where, say, two crystals touch, where atoms are arrayed irregularly or where impurities lurk.

At these interior hot spots, ice quickly melts to liquid or turns to water vapor. The result? Tiny, cave-like spaces filled with liquid, vapor or both, surrounded by ice. Depending on the intensity of the light and how quickly the ice melts, fern-like shapes or six-sided cavities may form. At cracks in the ice, Walker says, water-filled ovals may appear.