Summer is already approaching and long lines are forming in front of the ice cream parlors.
However, frozen food does not only exist as a treat.
As little as lemon sorbet seems to have in common with black ice, there is a great deal of agreement: in both cases, water molecules form the same hexagonal, i.e. hexagonal, crystal structure.
In it, the molecules are less densely packed than in liquid water, which is why ice floats on the latter.
Most other substances, on the other hand, are denser in the solid state and therefore heavier than in the liquid.
This oddity is just one of several anomalies in the compound H2O to which we owe our existence.
The eccentric character of the water also results in a unique variety of frozen things.
Twenty different types of water ice are known today.
The research numbered the range quite dry with Roman numerals.
Anyone who consumes ice cream, for example, will have the crystal type “Ih” melt in their mouth;
a subscript "h" stands for said "hexagonal".
Anyone who gets the idea of wanting to market higher-numbered ice cream varieties from this mineralogical range, such as ice cubes suitable for bars, be warned: Practically all of them only exist under very uncomfortable conditions - under enormous pressure and extremely low to sometimes amazingly high temperatures.
If you wanted to experience something like this, you would either have to go into the Earth's mantle or into the interior of icy moons.
That would be indigestible because the human body consists of almost 60 percent water, which would form an exotic form of ice there.
Such places are also technically inaccessible.
Boreholes do not go much deeper than ten kilometers, so they barely scrape the upper crust of the earth.
However, the interesting ice forms only form at a depth of hundreds of kilometers,
despite the heat there.
And space probes that could melt through the icy crust of Jupiter's moon Europa are unlikely to be seen any time soon.
Hydraulics and geometry push like 1500 tons
However, the conditions prevailing in such places can be created artificially, namely in high-pressure presses.
Two of them are in Hamburg.
Hanns-Peter Liermann leads us there through experimental halls on the site of the German electron synchrotron DESY.
They belong to PETRA III, a so-called storage ring with a circumference of 2.3 kilometers.
Inside, electrons revolve at almost the speed of light, which are tricked into emitting energy in sharp, intense X-rays.
These are led to various experimental areas secured with thick protective walls, including those where exotic types of ice cream are researched.
The answer to the question why X-rays are needed to study crystal structures will be given later.
Right now we are standing in front of "Aster-15", a hydraulic press in a nearly five meter high cage made of solid steel.
"It weighs about 45 tons," explains Robert Farla, who is scientifically responsible for it.
Six thick, blue-painted hydraulic arms can build up a pressure in all three spatial axes that corresponds to a weight of 1,500 tons.
In doing so, they press together an arrangement of movable stamps, which in this way transfer the force from a larger to a much smaller area.
Like a geometric transmission gear, this increases the pressure inside a sample chamber, which is only a few millimeters in size, to up to one million earth atmospheres.
However, this can only be achieved with special stamp materials, and only those made of a special diamond material can withstand the maximum pressure.
The sample chamber can also be heated up to 3000 degrees Celsius in order to be able to simulate temperature extremes at the same time as the pressure.