Broad Glass.
A method used widely in the 12 and 13th century found mainly in churches and cathedrals made by blowing a bubble of molten glass swung to create a tube this was then laid and flattened with the ends cut. Once cool the tube was cut into small rectangular lengths of sheet glass.
Crown glass.
Molten glass was spun producing a disc examples exist from the 14th and 15th century but when the tax on glass by weight ended cylinder glass became popular. Crown glass was made up to the 20th century.
Cylinder glass.
A type of Broad glass but with advanced methods employed it became possible to make larger tubes, this method became popular up to the beginning of the 20th century and many examples exist in private dwellings of that period.
Polished plate glass.
Developed in France glass was laid on a polish table and ground and polished to produce a clear sheet as mechanisation was being introduced glass for the first time was becoming less expensive this method was employed between the 18th and 19th century.
Drawn glass.
Often referred to as flat sheet. Molten glass was drawn between a die a bit like the old fashioned mangle used to wring clothes producing a flat continuous sheet.
This became the industry standard many examples still exist. It can be identified by the mottled effect and bubbles unless your property was bomb damaged during the war years or through some other breakage you probably have this type.
Float.
Invented in 1950 molten glass is allowed to flow over molten tin it results in a completely flat and featureless product of exact thickness and characteristics throughout.
Development in glass production from around the 16th century was reflected in the appearance of windows. Pieces of broad glass were laid in lead quarries but buildings still had often only one window that opened whilst servant quarters and low status rooms were not glazed, a waxed cloth was used along with shutters to keep the night out.
It was not until the 17th century that casement windows with sliding sashes became fashionable and with the onset of larger sheets of glass it became possible to fit these into rebates within the frame and glazing bars with metal sprigs were employed to keep the glass in place and finished in putty to keep the weather out.
The earliest sliding sashes had the top sash fixed. The lower one slid upwards and was held in place with pegs.
Not commonly known is that the double hung sash window that you see today was a British invention although the French like to think it was theirs! As they were the ones who came up with the bottom sliding sash. Using counter weights both sashes could be opened enabling a system of ventilation to be employed. The earliest example dates from 1701 and by 1750 most new development employed this system.
Many variations of this theme were employed and being British ridden by class the better off had swept heads (curved) , bowed, and elaborate decorative glazing bars. This can often be seen in fan lights above main entrance doors which also were becoming popular and stamped on the world a message of status.
Both Crown and cylinder glass was used during this period.
Glazing bars also were going through a development from large chunky Oak members to slender ovolo and quarter circle mouldings this in part was due to the import for the first time of cheaper softwood mainly Scandinavian pine. By the 19th century glazing bars were down to 12mm wide with pointed gothic mouldings.
With the introduction of cheaper plate glass from about 1830 which was stronger and available in larger pieces the need for glazing bars was reduced allowing for larger areas of uninterrupted views to the outside.
Wooden Window Repair 