These are really cool pictures. To me, this
phenomenon is somewhat reminiscent of "Pharaoh's
Snakes" fireworks (see Youtube?). In the case of
the sculpture, the zinc oxide wants to "get out"
from the penny and as it does so these tubes
Why are the tubes hollow? To be perfectly
honest, I'm not sure. Disclaimer: most of what
I'm saying is "educated conjecture." But I have
a couple of guesses. It could be a consequence
of the fact that at the molecular level, zinc
oxide exhibits crystalline structure. There have
been experiments in the last decade or so that
show that zinc oxide can grow in hollow tubes.
However, the size of the tubes in these
experiments was much smaller than what the
pictures you sent look like. The hollow tubes
could alternatively be the result of the zinc
oxide pushing its way through the clay, which is
porous. The size of the pores in clay, I think,
are more consistent with the size of the tubes
that formed (on the order of mm or so).
And why are the tubes spiral? When I look at the
pictures, the tubes look like they were pushed
out one little "bit" at a time. It looks almost
as if some zinc oxide might have formed, pushed
its way out, more might have formed, and pushed
its way out and so on, but very rapidly.
One interesting thing you might do if you
the time/resources is to try to reproduce this
and see if the same thing happens; and if time
and resources allow, maybe try it with the
pennies embedded more deeply in the clay?
Sorry that I didn't give any really solid
answers, but I hope this helps. It was
interesting thinking about this question --
thanks for bringing it to our attention!
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