Tapier, a gifter from the german north sea coast recently published on the german forum these nice pictures of ice plugs which had formed in the tubes of his CB. He discovered them when he was pulling out the crystals for inspection.
What a cool surprise.
There is clearly to see a vortex-structure in the
core of the ice plugs.
Above the crystals there had formed a funnel-like
cavity which then continues in a thiner, somehow
twisted cavity. Enjoy!