Back when I lived in Boulder CO, I worked with Charles Knight on developing a new way to grow ice crystals for experimental study. I knew that the problem with most methods was twofold: there were too many crystals too close together to be able to learn how each one behaved on its own, and the surface that held the crystal would influence the crystal’s growth. Charlie hit on a great way to eliminate the first problem: put some water in a small pipette (like a narrow, tapering straw) and freeze the water from the wide end. At the tip, which stuck out into a small observation chamber, ice would grow out as a single crystal. Unfortunately, the smallest pipette tip was about a millimeter in diameter, which is too large. I then tried using Dupont hollowfill fibers, which are about 20 times thinner – about as thick as fine human hair. But this was still too thick. So I started using glass capillaries, which I could heat with a small torch to draw down to sizes 100-1000 times thinner than the pipette – about as thin as small cloud droplets before they freeze into ice. We had our method. From the start we would see things that hadn’t been reported before. Some of these things we (or I) published, but most of the things still remain unpublished. One of them is the heart-shaped crystals. The photo below shows the tip of the capillary, which is about 10 times thinner than human hair, along with a thin heart-shaped crystal.

 

 

After the heart grew a little more, it developed into a hexagonal shape. But probably the most bizarre thing I saw occurred when I decided, just for kicks, to try to evaporate ice from the inside of a crystal by connecting the wide end of the capillary up to a vacuum pump.

As I pumped, ice evaporated from the inside in the shape of a thin disc-shaped region. I started snapping pictures. In my excitement, I went down the hall and told Greg M- to come see the ‘negative crystal’ growing inside my crystal. (Note that part of the original crystal, an elongated hexagonal crystal, lies outside the frame of the photos below.)

 

 

As Greg looked into the eyepiece, he said something about a third crystal. I said that there were only two, but then I looked in the eyepiece and saw a new disc crystal growing inside the evacuated (negative crystal) region. I don’t know how it got started, but I shut off the vacuum and started watching it grow. According to my calculations, there was a temperature gradient inside the original crystal such that the center region was cooler than the outer regions. This gradient, I think, is the reason the interior disc crystal grew; water molecules evaporated (or, more correctly, sublimated) off the sides of the negative crystal and deposited on the cooler sides of the disc crystal, making it grow. But as it grew, the lower part came closer and closer to the walls of the negative crystal. Meanwhile the top of the crystal hardly grew near the capillary tip; instead, it grew around the capillary, resulting in a heart-like shape.

- JN