Glass is based on the premise that while here, the top group of panes looks vertical and the bottom group looks horizontal, ...
... if we see only a small subset of these clusters, we cannot distinguish them.
So the two states exist in superposition, until we reach an edge, where typically one particular orientation is favoured. This represents a measurement in quantum mechanics: the collapse of the wave function.
* The Consistent Histories Interpretation, proposed by R.B. Griffiths (1984) and elucidated by the late Pierre Hohenberg in his Reviews of Modern Physics article (2009).
** This statement is shared by all interpretations of quantum mechanics.