It's a plot device... a way to cast a
reflective plate
glass window against the
larger theme of the dissolution of, well, take your choice.
If one sees Mirror Strata (a
large piece formed by overlaid strips of
glass) as sculpture, for example, it is necessary to negate the
reflective aspect of its material while, on the other hand, if one concentrates on its surface, then its solidity as an object disappears.