Cylinder glass (historic window glass)
Cylinder glass here means historic window glass made by blowing a large cylinder, removing its ends and cutting it lengthwise. Reheating allowed it to be flattened into a sheet. After annealing, the sheet was cut into panes. The term therefore describes manufacture, not merely an object with a cylindrical shape.
Tafelglass in Norwegian sources
Nøstetangen Norwegian Glass Museum uses the name tafelglass for glass made by opening and flattening blown cylinders. It documents this production at Nøstetangen. The Norwegian encyclopaedia Store norske leksikon also discusses the cylinder method in connection with Drammen Glassworks. See Drammen Glassworks for the works' own history.
Difference from crown glass
Cylinder glass starts as an elongated hollow form opened into a sheet. Crown glass, by contrast, is formed as a spinning disc. Both historic methods can produce waves and varying thickness. Distorted reflections in a pane are therefore insufficient to establish which method was used.
When buying or recording
Document dimensions, edge finishing, surface and mounting. Distinguish manufacturing traces from scratches and later damage. An old frame does not prove that its glass is original. Nor does a pane matching the description of cylinder glass establish Norwegian manufacture or a particular glassworks.
Sources
Corning Museum of Glass: Cylinder glass; Nøstetangen Norsk Glassmuseum: Vindusglass; SNL: glassforming; Historic New England: A History of Window Glass.
