In this case, in search of improved realism, has been used a background image to build geometry, applying a material that emulates the behavior of light more fideligna.
There are two possible explanations widely known on the symmetry of snowflakes. First, could have communication (data transfer) between arms, so that the growth in each arm affects the growth of the opposite end. The tension the surface phonons or is one of the ways in which such communication could occur. The other explanation, version seems to be a prevailing, is that the arms of a snowflake independently grow in an environment that is thought to vary rapidly in their temperature, moisture, etcetera.(W)
In the images attached can be observed parameters used to define the material that generated the ice effect.
The result can be seen in the following image, that can be used as wallpaper in this Christmas. Clicking on the image gives the snowflake wallpaper format with resolution 1280 x 1024