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Natural Snowflakes
  --Photo Gallery I
  --Photo Gallery II
  --Photo Gallery III
  --Guide to Snowflakes
  --Snowflake Books
  --Historic Snowflakes
  --Ice Crystal Halos
  --Snowflake Store
Designer Snowflakes
  --I: First Attempts
  --II: Better Snowflakes
  --III: Precision Snow
  --Snowflake Movies
  --Free-falling Snow
  --Designer's Page
Frost Crystals
  --Guide to Frost
  --Frost Photos
Snowflake Physics
  --Snowflake Primer
  --Snow Crystal FAQs
  --No Two Alike?
  --Crystal Faceting
  --Snowflake Branching
  --Electric Growth
  --Ice Properties
  --Myths and Nonsense
Snow Activities
  --Snowflake Watching
  --Photographing Snow
  --Make Your Own
  --Snowflake Fossils
  --Ice Spikes
  --Activities for Kids
Snowflake Touring
  --Snowflake Hot Spots
  --Northern Ontario
  --Hokkaido, Japan (2) (3)
  --Michigan U. P.
  --California Mountains
Copyright Issues
Designer Snowflakes - Part Two
   ... Better snowflakes ...

   Our initial successes (see Part One) showed that it was possible to grow some excellent designer snow crystals on the ends of electric ice needles.  But getting everything working right -- the temperature, humidity, and optics -- was going to be difficult.

Better Hardware ...

labpic2x.jpg (9284 bytes)   Our simple diffusion chamber wasn't sufficient to engineer really nice snowflakes, so we built a new and improved snowflake growing machine.  We did some systematic studies of electrically modified crystal growth with this chamber, and along the way we took more pictures.
   Along with a better chamber, we also used a high-quality long-distace microscope, along with a large-format CCD camera, to get substantially better photographs.

... makes Better Snowflakes
    This image shows a small plate-like crystal, which was grown at a temperature of about -13 C, slightly warmer than the dendrite peak (see the snow crystal primer for details). As with most of the snow crystals displayed here, the crystal was created by first growing a thin "electric" ice needle (click here for details). Once the ice needle had reached the desired length, the high voltage was turned off, and the crystal was moved to a region in the growth chamber that had the desired temperature. At this point the plate-like crystal began growing at the needle's tip.
    The tip-to-tip diameter of this crystal is about 0.6 mm, which took about ten minutes to grow. The water vapor supersaturation level was not measured with high accuracy, but here is estimated to be around the water saturation level.
    Note the sectored plates in this crystal, some of which are strongly reflecting the light, and the characteristic ribs on the plates. The "shadow" in the lower left of the image is in fact another growing snow crystal, behind the one the camera is focused on.
   In this image one sees another example of sectored plates. This crystal began growing close to the dendrite peak, so that six dendritic arms sprouted from the needle tip. Because the supersaturation level was low, the arms exhibited only slight sidebranching. After the arms had developed, the crystal temperature was raised a few degrees, and the supersaturation level was reduced, then favoring the development of sectored plates at the ends of the dendritic arms. Finally, near the end of the crystal growth the temperature was again lowered to the dendrite peak, which caused ridges to form along the outermost edges of the sectored plates. The crystal diameter is about 0.8 mm.
    All the images shown on this page were originally acquired in black-and-white using a megapixel CCD camera. The images were cleaned and processed to varying degrees using PhotoShop, and color was added for artistic effect.


   Here's a good example of a designer snowflake. It was grown at about -14 C, quite near the dendrite peak, and at a fairly low supersaturation. Under these conditions the needle tip immediately sprouted six dendritic arms. At various times during growth the crystal was moved to -7 C for just a few seconds, and then moved back to -14 C; this operation caused a pair of sidebranches to sprout from each of the six main arms. All the sidebranches on the crystal were induced using this procedure; none grew otherwise. Tip-to-tip diameter is 1.8 mm.
    This crystal also demonstrates the phenomenon of kinetic roughening. At the tips of the main arms the supersaturation is high, making the tips rounded. Closer to the center of the crystal the supersaturation is lower, and thus the sidebranches are faceted.
  See Snowflake Movies for a movie of this crystal growing.
   This crystal began at -15 C, where six branchless dendritic arms grew from the needle tip. Once the arms had grown a bit, the crystal temperature was raised to -13 C and the supersaturation was reduced. Then sectored plates proceeded to grow from the ends of the dendritic arms. Right before the picture was taken the crystal was moved to -15 C again, and dendritic arms just started growing from the tips of the sectored plates. Diameter is about 0.8 mm.


   At right is a combined image of the above four. Click on the image for a full-sized version.. The sizes and growth conditions of the various crystals are given above. Growth times varied from about 15 - 45 minutes. Dendritic arms grow at typically 1 - 3 microns/second, which can produce a 1 mm diameter crystal in about 5 minutes. Sectored plates, on the other hand, grow more slowly.


   Here are several examples of hollow columns grown at the ends of electric needles. For each of these crystals, once the electric needle had grown to some length (at a temperature of -4 C, just above the needle peak), the voltage was turned off and the crystal moved to a slightly lower temperature area. At this point a hollow column grew at the needle tip, while the rest of the needle slowly thickened. The first image shows a crystal grown at about -8 C. The second image shows a crystal grown at about -9 C; the two upper inset views show early times during the growth; the lower inset shows a end-on view, with light reflecting from the rim of the column. The third image shows a crystal grown near -7 C, producing a somewhat longer, thinner column.


   More dendritic designer crystals. The one on the left was grown near -15 C, with excursions to a slightly higher temperature to promote sidebranching. The final phase of growth was at -15 C, at which temperature the main arms grow rapidly in the form of sharp spikes. The image on the right is side view of a dendritic start, early in its growth.


   A fairly large crystal, approximately 2 mm in diameter. The ambient temperature varied slightly during the crystal growth, changing from about -14 C to -13 C. Note that there is a great deal of structure in the sectored plates at the ends of the arms, reflecting the somewhat higher supersaturation (compared to the pictures above) during growth.

   Electric needles can be coaxed to grow along different crystallographic axes of ice, and these two columnar crystals formed on electric needles that had grown along an a-axis. The first crystal was grown near -7 C, becoming a hollow column (the hexagonal shape can be seen in the enlarged image). The second was grown at -5 C, showing a collection of thin ice needles. Note that the electric needles, grown along an a-axis, are quite rough. This is in contrast to the previous images, where the electric needles were grown along the c-axis, which can result in very smooth hexagonal needles, the same shape as wooden pencils.

   Left: Another snow star, grown near -13 C at fairly high supersaturation. The dendritic arms show copious sidebranching in the form of small plates. The electric needle evidently had small imperfections just below the tip, which resulted in the growth of small plates below the main crystal. Note these small plates have the same orientation as the main crystal, demonstrating that the entire assembly is a single crystal. Right: An oblique view of a dendritic star, grown at -15 C and high supersaturation, which produces many fern-like sidebranches on the main arms. Note how the crystal grows upward, since the top basal surface is at a higher supersaturation level than the lower surface.


   Left: A nice shot of a scroll-type hollow column, growing from a clump of crystals. Note how one wall of the cup-shaped crystal is curled inward. Right: a chain of hollow columns, growing at around -7 C with fairly high supersaturation.


   Left: A side-view of a growing dendritic star, with thick, somewhat structured plates. Note the facets visible in the supporting needle crystal. Right: A peculiar snow star, grown around -10 C (midway between columns and plates), at high supersaturation.


   Another designer snowflake, which we call a "chandelier" crystal. After growing an electric needle, the voltage was removed and the temperature lowered to around -15 C to produce a small stellar crystal. This was then moved to about -7 C, which caused hollow columns to grow from the tips of the stellar branches (left image). Finally, this same crystal was again lowered to -15 C, resulting in more dendritic branches growing out from the hollow columns (right image). From this perspective it is a bit difficult to pick out all six branches of the crystal.


   This image shows a dendritic star crystal in light reflecting directly off the shiny flat surfaces of the plate-like sidebranches (using a bright, point-source lamp for illumination). Similar, very flat, basal facets are often seen on snow crystals falling in cold climates.

Return to was created by Kenneth G. Libbrecht, Caltech
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