Cylinder blown sheet is a type of hand-blown window glass. It is created with a similar process to broad sheet, but larger cylinders are produced by swinging the cylinder in a trench. The glass is then allowed to cool before the cylinder is cut. The glass is then re-heated and flattened. The result is much larger panes and improved surface quality over broad sheet.
In this manufacturing process glass is blown into a cylindrical iron mould. The ends are cut off and a cut is made down the side of the cylinder. The cut cylinder is then placed in an oven where the cylinder unrolls into a flat glass sheet. William J. Blenko used this method in the early 1900s to make stained glass. These imperfect panes have led to the misconception that glass is actually a high-viscosity fluid at room temperature, which is not the case.
Other methods of producing hand-blown window glass included broad sheet, blown plate, crown glass and polished plate. These methods of manufacture lasted at least until the end of the 19th century. The early 20th century marks the move away from hand-blown to machine manufactured glass such as rolled plate, machine drawn cylinder sheet, the Fourcault process of flat drawn sheet, single and twin ground polished plate and most common, float glass.
Cylinder blown sheet glass was manufactured in the UK in the mid 19th century. It had been manufactured in France and Germany (and imported to the UK) since the 18th century.