Just my luck! Not many snowstorms create colourful snowflakes, and when they do they are usually smaller hexagonal gems. I was thrilled to encounter this vibrant flower in a slightly large crystal!
The colour here is well understood, but still magical. It’s not colour in the same sense as you would paint with (the paint would absorb certain wavelengths of light and reflect others, you see the reflected light), but rather generated through optical interference. This is the same physics that generates colours in soap bubbles, but in a snowflake is often much more structured.
One way or another, a bubble forms in the ice. The thickness of this bubble dictates the thickness of the ice on either side of it, and shifts in this thickness will change the resulting colours. Light bounces off of reflective surfaces, but a snowflake is ice, not a mirror; some light still enters the snowflake and reflects back off of the additional boundaries between ice and air. When light passes through a denser material (ice), it slows down, and when it reflects back out, it speeds up again. This is critical. If the distance traveled through the ice is small enough, the two rays of light will rejoin, but half of it will be “out of sync”. This causes some wavelengths to cancel out while others are added together, generating specific colours from otherwise white light. Very similar principals apply to sound waves and interference.
Once the bubble is completely enclosed, things can still change. Water molecules can break away from their crystal structure (sublimation) and re-attach elsewhere. This might slightly change the thickness of the ice in certain areas but in a gradual fashion. I suspect this is the reason for the gradient from yellow to magenta at the tips of the internal “petals”.
The central bubble here is fascinating for other reasons as well – just look at the outer edge of it. Notice these little “nubs” in each corner? Imagine the snowflake being just that big. Those little nibs would be the last elements to stay open to the outside air before shifts in temperature and humidity allow the outer edge of the snowflake to become whole again. What’s interesting here is that a snowflake typically grows fastest where it has the greatest access to water vapour – the corners. Why then did the corners take the longest to close up? Moreover, why did the middle of each prism facet also have a nub, which continued to progress a line-like bubble that eventually evolved into a sectored-plate design?
It’s a beautiful physics puzzle and fun to spend some time imagining how and why it came to be.
Shot on a Lumix S1R with a Canon MP-E 65mm macro lens. I’ve used a lot of ring flashes over the years, but my favourite is also one of the most affordable – the Yongnuo YN-14EX II: www.bhphotovideo.com/c/product/1462725-REG/yongnuo_yn_14e... . It’s better in many ways than Canon’s own MR-14EX II, and it’s what I’ve been using to shoot the snowflakes in this year’s series. For more tips on snowflake and general macro photography, you can also check out my upcoming instructional book, Macro Photography: The Universe at Our Feet - skycrystals.ca/product/pre-order-macro-photography-the-un...
For those curious about how the book is progressing? Coming along nicely! Most of the book is just undergoing revisions and grammar checks but there is still more work to be done. I appreciate your patience. :)