Akira's Corner Pockets

May 10th, 2016

The evanescent snow crystal

appears out of nowhere

The lines and boundaries

on its faces record a story

a story of a crystal's birth

a story of a crystal's life

But before the record vanishes

Who will hear its story?



A few years back, a correspondent of mine, Professor Akira Yamashita of Japan, long retired, sends me an email. In the email, he had a document with words and pictures of some small crystals that he'd captured back in the 70s. They were small crystals, essentially freshly "hatched eggs" from the frozen droplets upon from they had started. But some had small pockets of air near their corners.

To those who have studied any sort of crystal growth and have some familiarity with crystal-growth theory, these corner air pockets, or "bubbles", were in impossible locations. They should not be there. Pockets will form near face centers, not corners. But Prof. Yamashita also had a theory about their formation. His theory first looked sketchy to me, but I appreciate hearing about new ideas, so over the following years kept revisiting his theory, getting to think that it had merit, and wondering if it had other applications.

Then, just this past year, in our own ice-crystal experiments, we did something that apparently had never been done to small ice crystals in the lab before. We slowly grew a crystal in air. And we cycled it from slightly growing, to slightly sublimating (i.e., shrinking in size), to slightly growing again. A cycle that must happen in some regions of cloud. And here is what we saw:




Corner pockets!


After the sublimating, the subsequent growth kept a permanent record of the sublimation cycle in the form of 12 corner pockets, one pocket for each of the 12 corners of the crystal. These are pockets of air, just like the six large 'petal-shaped' pockets of air you see nearer the center of the crystal. They are forever stuck in the crystal. Stuck there until the crystal, with all of its features, vanishes back to air.




After seeing this, we ran a few more experiments, and each time we slowly grew, then sublimated, then grew again, we got corner pockets. The name 'corner pockets' refers to their location when they are formed; namely at the corners, next to the crystal perimeter. However, they remain essentially fixed in position as the crystal grows, and this means that as the crystal perimeter expands outward, the corner pockets will appear further within the crystal. Analogously, the 'center pockets' shown above formed at the face centers, on the crystal perimeter, back when the crystal was much smaller.



As to the theory of their formation, and how the theory can explain other observable features of snow crystals, you'll have to wait for a subsequent post.



- Jon

Story of Snow - Simplified Chinese edition

April 6th, 2016
Story of Snow - Simplified Chinese edition
A few copies of the simplified Chinese Edition of The Story of Snow arrived at my house a few days ago - here's what it looks like:

The Story of Snow was originally published over 6 years ago (October, 2009) - so it's great to see continued developments even now. It of course remains in print in English and available at places like Amazon. -- Mark

100 Snowflake Photos

January 27th, 2015

I recently put together a new collection of 100 snowflake photos. The gallery ranges from some of the first photos I made (on film) in 1999 through photos made in early 2015. If you are interested in seeing more snowflake photos, follow this link: 100 Snowflake Photos (or click the snowflake photo below). Enjoy!

More 2015 Snow Crystals

January 27th, 2015

A few more snowflakes from recent days (January, 2015)... click the images for much larger files on flickr.

Note - to keep from cluttering the blog here, I am just adding new images as I take and process them. So stop back to see new stuff!

-- Mark C.

Added January 27, 2015:

Added January 15, 2015:

Added January 13, 2015:

Added January 9, 2015

January 2015 Snow Crystals

January 6th, 2015
At long last a snow that produced some intact crystals... Here are two from this afternoon, January 6, 2015 (click on the images for much larger files.)
Hopefully, more will be coming! Mark C.

Standard P1a Hexagonal Crystal, Front and Side

December 19th, 2014

It didn't start so symmetrical, but became so as it grew:

This, the left crystal of the pair described two posts below, grew much more slowly on its basal faces (front & back in the left image). The way it grew, and its big difference with the crystal on the other capillary (described two posts below), indicates crystalline perfection on the basal faces. Imperfections on the other crystal caused its basal faces to grow relatively fast.

The bands of dark and light on the rotated crystal (right side above) suggest different facets. But the light regions are instead regions where the light, coming from the back, can go through two parallel (or nearly parallel) faces. Thus, the light region is actually less than a complete facet, whereas the top dark region is a combination of two facets. See the facet-by-facet comparison below:


Lots of Hair Ice

December 19th, 2014

My older sister sent me this photo on a recent morning.

This is hair ice growing from an alder tree. All of it grew overnight, formed when liquid water near the outer trunk surface (beneath the bark) froze. This creates an ice front in each pore-like structure. Water inside the trunk flowed out to the ice front, pushing each hair-like strand of ice outward.

It probably does not get as cold under bark unless the bark is partly peeled off, so the hair ice comes out of bare spots in the trunk, as shown in the photo above. The air temperature got down to 26 F that night, and the tree was next to a dirt road, and thus partly exposed to the sky.

Like the needle ice that grows out of the ground, it grows relatively fast, producing relatively long hairs. From another spot, down near a meadow:


A Crystal Pair, Several Views, and a "Man on the Crystal"

December 19th, 2014

One advantage of the new apparatus is the capability to grow up to three crystals at a time, each on its own capillary. It is also very useful being able to move each capillary around. Having success with a single crystal, we tried it with two, and much thinner, capillaries.

This time, we had to cool the apparatus down to about -38.5 C before they appeared (previous cases were about -20 C), and to my surprise, they both appeared at about the same time. (Polycrystalline blobs, as are more common at these low temperatures.) Due to some troubles we were having with the vacuum (later discovered to be simply a case of the pump getting shut off), we warmed the crystals up to -17 C, sublimated them, and regrew them.

The capillaries slide up-down on axes that intersect, designed this way so we can bring the crystals nearer or further apart. For the above image, they were relatively close. The crystal on the left is a thin plate, whereas the one on the right appears to be a short column. Both grew under the same conditions, but grew into different forms.

On closer look, the rightmost crystal revealed itself to be more interesting than initially thought:

The apparent "man in the crystal" (i.e., face, as in the "man on the moon") shown in the view above arises from dark lines, which are due to face-face edges on the other side of the crystal, a horizontal "terrace", also on the other side, plus an air pocket inside the crystal.

Also, the crystal appears to be eight-sided around the perimeter, but this is again an illusion due to perspective. Rotating the crystal around the main capillary axis instead suggests a four-sided form:

Whereas another rotation suggests a common hexagonal prism:

The horizonal extent of the crystal is about 150 micro-meters (microns). The view above clearly shows the interior air pocket. Also, on the right, you can see the profile of the "terrace" mentioned above.

Another rotation, giving another view, helps to clear up the mystery of the 3-D crystal shape:

The crystal is a short hexagonal column, but two opposite prismatic faces are much larger than the other four (because they grew much slower). I copied the crystal image at right and outlined the crystal edges in red. This shape of crystal is thought to give rise to one of the "Parry arcs" in the sky, which I showed in an earlier post.

Another interesting thing about this crystal is its very weak attachment to the capillary. The molecular forces holding it up were so weak that torques arising from the pull of gravity would cause the crystal to slowly rotate downward. In general though, these cases show how useful it is to be able to move and rotate the crystals.


New Capillary Crystal-Growth Device

December 11th, 2014

After several years of planning and several more years of construction, our new crystal-growth device is operational. We are now tuning the electronics, vacuum system, data collection method, and other aspects, but we can indeed produce ice crystals on a glass capillary under controlled conditions.

The thing works!

The first two capillaries we tried basically exploded, due to my having loaded them with way too much water, but the third produced a nice frozen droplet. The frozen droplet, or "droxtal" did not grow on account of all the water that had spewed down from the previous attempts, but we cleaned up the debris, and started anew. That case, pictured above, produced a nice spatial dendrite. I could control the growth condition quite well, and kept growing, sublimating, and regrowing the same crystal for a few days. We now need to refine our capillary-making method and make them about 10x thinner (as I used to do in my previous experiments).

The overall setup is pictured below, Brian at the controls.

The white thing on the right is the cooler. It pumps cold methanol into the big aluminum box sitting on the table. That box is actually three boxes: an innermost crystal box (consisting of several chambers), a bath box that holds the cold methanol cooling fluid, and a vacuum box around that to help insulate the system.

All the controls enter from the top, so we have lots of things sticking up on top: fluid in-out ports, vacuum control of the growth chamber, reference chamber access, access to two vapor-supply chambers plus vacuum control of the chambers, a valve system to connect vapor to growth chambers, and a bunch of wires... The inside of the innermost crystal box is gold-plated to deter corrosion and help us keep contaminants to a minimum.

We hope to have more crystal images soon.


Freezing a Soap Film

December 1st, 2014

Upon seeing this morning some recently posted pictures of freezing soap bubbles, I decided to give it a try.

Fortunately, we have been having freezing temperatures recently. And coincidentally, my older daughter had just purchased some glycerin for making hand lotion. (Glycerin is a very useful ingredient in soap-solution.) I mixed up a cup of solution, using crushed ice in the water to make it cold, found a bit of twine, and headed outside to a shady spot in back.

I soon gave up on blowing bubbles, and just tried freezing a film. It worked on the third try:

(As with all images on this blog, click to enlarge.)

Sometime later, I will work on freezing larger bubbles. I imagine though that if I had my polarizing sheets with me, even a frozen film could dazzle. Next time.

If you have experience freezing large bubbles, please let me know. My ice films would break within about a minute of the first signs of ice formation--it would be nice to know a better method.

- JN