Crown glass (historic window glass)
Crown glass here means historic window glass made by blowing and opening a glass form, then rotating it into a large flat disc. After cooling and annealing, the disc could be cut into window panes. This article uses the term for window glass and its manufacturing method, not as a general quality label.
The central bull's-eye
The disc was thicker at its centre where it had been attached to the pontil. Panes cut from this area may retain a conspicuous bull's-eye. Not every pane cut from the same disc contains that mark. The absence of a visible bull's-eye therefore does not rule out crown glass.
Norwegian glass history
Nøstetangen Norwegian Glass Museum documents the production of both crown and cylinder glass at Nøstetangen. A pane's appearance alone is nevertheless insufficient to attribute it to that glassworks. Read about Nøstetangen Glassworks too.
Assessing older panes
Examine surface waves, varying thickness and possible tool marks. These features relate to manufacture and are not a reliable age scale. Cylinder glass can also be uneven. Record dimensions, edges, framing and earlier repairs. Do not remove an old pane from its setting merely to examine it more closely.
Sources
Corning Museum of Glass: Crown glass; Nøstetangen Norsk Glassmuseum: Vindusglass; Historic New England: A History of Window Glass.
