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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 One
   ... First attempts ...

   While studying the physics of how snow crystals form and grow, I also became interested in the art of growing synthetic snowflakes.  These are basically identical to what falls from the sky, except they are made in the lab under controlled conditions.   I also like to call them designer snowflakes, since in principle one could design whatever shape one wanted ... within the bounds of the crystal-growing physics, of course.

   Why make designer snowflakes?  Partly it's the challenge of reproducing what's found in nature, and perhaps doing better than nature.  There's also a sound scientific motivation for making designer snowflakes, since often the best way to understand a phenomenon is to try and reproduce it in the lab.   One might even learn something interesting about crystal growth along the way.

The Art of Growing Snowflakes

The Diffusion ChamberStart with a Diffusion Chamber
   There are many ways to grow snowflakes (see the Designer's Page), but my favorite starts with something called a vapor diffusion chamber.   This is essentially nothing more than an insulated box that is kept cold on the bottom (say -40C) and hot on the top (say +40C).  A source of water is placed at the top, and water vapor diffuses down through the box, producing supersaturated air.   The cold, supersatured air at the center of the chamber is ideal for growing ice crystals.
   Our first diffusion chamber was the rather simple affair shown at right -- mostly made of plexiglas and styrofoam.  I worked with Caltech undergraduate Victoria Tanusheva to make our first designer snowflakes in this apparatus in the summer of 1997. 

Electric Needles
   While working with this diffusion chamber, we rediscovered a wonderful technique for growing synthetic snow crystals that was first published in 1963 by meteorologist Basil Mason and collaborators [1].  One starts by putting a wire into the diffusion chamber from below, so that small ice crystals begin growing on the wire's tip.  Then apply a high voltage to the wire, say +2000 volts, and voila -- slender ice needles begin growing from the wire.
   The great thing about electric needles is that you can grow snow stars on their ends.  The picture at right shows five electric needles growing out from our initial ice-covered wire, and each needle is topped with a snow star.  The right image is a negative close-up of the same cluster of needles (from a different viewpoint); the diameter of the snow star is 2.4 mm.
   In addition to the pretty pictures, we also spent a fair bit of time puzzling over exactly how the electric needles grow, which we showed was because of an electrically induced growth instability [2].
Snow Stars

Click for a larger image   These two pictures show a well-formed snow star growing at the end of a long electric needle crystal.  The left image is after about 10 minutes of growth, the right image about 5 minutes later.  The diameter of the star in the right-hand image is roughly 2.5 mm.  The temperature of the crystal was varied with time to change the crystal growth morphology, giving the crystal its unique form.

Here is another large dendritic star; the right-hand image shows the star after the background crystals were carefully removed. 

Two shots of a cluster of numerous snow stars growing on electric needles.
starscomposite2x.jpg (24943 bytes)Moviemaking
   This time series of pictures shows the growth of a large star (final diameter about 4.5 mm).  First the wire was placed at a position in the chamber where the temperature was -5C and an electric needle was grown (see Electric Growth).  Then the voltage was turned off and the needle moved to -15C, where a stellar dendrite formed.  Then the temperature was cycled between roughly -15 C, which gave rapidly growing dendritic spikes, and -12 C, which produced more-slowly growing sectored plates. Each of the sub-images is shown at the same scale. 
   See Snowflake Movies for some movie clips of growing snowflakes.
Here are some random dendrites grown in our diffusion chamber, which form at a temperature of around -15 C.  Note the appearance of sectored plates in some of the images, which results from lower supersaturations.

Some typical needle-like crystals which grow around -5C.
The Hardware
   This shows a schematic view of the vapor diffusion chamber.  Dimensions of the inner box are 15x15x32 cm.  The bottom plate was cooled to as low as -50 C while the top plate was heated to as high as 40C.  The temperature gradient created a stable environment since warm air floats on top of cold air.  Water vapor diffused downward to make supersaturated air in the center of the chamber.
   Crystals were grown either on the tip of a tungsten wire (left) or along a nylon string (right).  The three layers of chamber walls were made from acrylic sheet, with styrofoam insulation between layers.  
The Diffusion Chamber    Imaging was done from the side, using a standard video camera attached to one eye of a stereo microscope.  Images were digitized using a Snappy frame grabber, with SnapCap software for time-lapse imaging.  (This was before the era of cheap digital cameras!)  The images were all digitized at a resolution of 640x480 pixel resolution, and typically have a scale of 10 microns/pixel.  .
Victoria TanushevaAnd finally we have a picture of Vicky Tanusheva at the helm.
[1] J. T. Bartlett, A. P. van den Heuval, B. J. Mason, Z. angue. Math. Phys. 14, 509 (1963).

[2] "Electrically Induced Morphological Instabilities in Free Dendrite Growth," K. G. Libbrecht and V. M. Tanusheva, Phys. Rev. Lett. 81, 176 (1998). (see our published papers)

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