Plastination involves replacing the water and fats in the tissues with silicon or some other polymer. The specimen is first fixed in alcohol, then dehydrated, impregnated with the polymer and finally allowed to harden.
In the photograph above, the coronal brain sections have been placed under ultraviolet light for curing. The black stains visible in the slices show the sites of a massive haemorrhage which killed this individual.
Pay attention folks. This is the first step toward uploading your brain into a computer!
Too bad some important parts of this man's brain were obscured by the hemorrhaging.
The sections don't show massive hemorrhage (in fact there's no evidence of mass effect). They show bilateral, roughly symmetric hemorrhagic infarcts involving arterial border zones of the cerebrum and cerebellum, which would've been due either to severe systemic hypotension with reperfusion or (less likely) a shower of small emboli from atheromatous plaque in the aorta.
Just my $0.015..