Against the background of black ice, the late afternoon’s blue sky turned to indigo (above) while the crystals inside the bubbles catch sunlight and scatters it in all directions.
When the sun is near the horizon, its light scrapes across the surface and illuminates individual snowflakes waiting for a breeze to scoot them across the smooth surface. Perfectly round as well as irregularly shaped bubbles as large as a foot across are embedded in the ice only a quarter-inch under the surface (below). In other spots, the bubbles may be several inches beneath the surface or stacked in successive ice layers. A video titled “Ode to Ice” on ScienceFriday.com explains how oxygen is forced out of water as it freezes and can either fill the ice with microscopic bubbles or create perfectly clear slabs depending upon conditions (5:26 minutes. Explanation of bubbles in ice at about 2:30).
Here are three other examples of bubble gardens on the Brighton millpond. They aren’t great photos but show different bubble patterns along the millpond trail.