Windows were Tiffany's first love, but they are much rarer.  Each is also unique, unlike the lamps.  They represent a higher level of expertise in artistry and craftsmanship, having glass selected by master colorists, and being manufactured by the Studios' best craftsmen usually with multiple layers of glass.  More of Tiffany's windows, installed in buildings that were demolished, were also lost, while Tiffany's lamps were often packed away.  Until recently, they were actually less valued than lamps.