  Strangeness flavor has turned out to be a very effective diagnostic tool of
relativistic heavy ion physics. The absolute yield provides information about
conditions arising in first instants of the interaction. Strange hadrons are
abundant allowing a precise study of the chemical freeze-out conditions in the
dense matter fireball. The thermal and chemical freeze-out universality seen in
strange hadrons confirms sudden hadronization as the breakup mechanism. A
plausible cause of sudden fireball breakup is the mechanical instability
arising when a quark-gluon plasma phase supercools deeply in its adiabatic
expansion. Applying these ideas, we interpret CERN-SPS and the first results on
hadronic particle ratios obtained at RHI
