  The possibility of observing a glass transition in water before
crystallisation occurs has been debated vigorously but inconclusively over five
decades [1,2]. For two decades a glass transition at 136K [2,3] was accepted
but this transition has perplexing qualities [4]. Recently it has been
argued[2,5],that this assignment must be wrong. The re-assignment of Tg to
temperatures above the 150K crystallisation was vigorously contested [6]. Here
we use detailed anneal-and-scan studies of a hyperquenched inorganic glass,
which does not crystallize on heating, to interpret the perplexing aspects of
the 136K water phenomenon. We show that it is indeed linked to a glass
transition, though only via a cross-over phenomenon. The thermal history that
gives the same behaviour ("shadow" glass transition) in the inorganic glass is
linked by crossover to a "normal" glass transition 23% higher in temperature.
Thus a Tg is indeed unobservable for water, while the vitreous nature of
hyperquenched glassy water is strongly supported. The shadow Tg is reproducible
in the inorganic glass as it is in H2O. The observed aging dynamics are very
relevant to current glass theory, particularly to dynamical heterogeneity which
is seen to have an energy manifestation.
