Period Flat Glass
See also Tube and Sheet Glass Making #SHEET
Back to Good Old Days Center
2009-06-19 Rev. 2011-02-04,
Period Window Glass
|CROWN GLASS: Fig. 1 shows the glassmaker having spun the table of Crown, about to drop it into a bed of sand (note the early version of virtual reality headgear||BROAD GLASS: Fig. 2 shows part of the process of Broad Sheet manufacture. ‘d’ shows the muff about to be sheared open, ‘h’ shows the sheet after flattening|
|PLATE GLASS: Fig. 3 This shows the French process of Cast Plate manufacture. The box of molten glass on the jib has been turned over and the molten glass is poured onto the casting table and the large iron roller will be passed over the glass to make a uniform thickness prior to polishing and grinding||BROAD GLASS: Fig. 4 The title is misleading as this shows the manual polishing of Broad Glass to turn it into Blown Plate. Wooden blocks mounted on a willow spring, have felt pads underneath and fine polish such as jeweler's rouge is used to finish off sometimes before turning into mirrors|
PRESERVING AND RE-USING ORIGINAL GLASS Where old glass exists in good
condition, it should, if at all possible, be retained. When this is not
possible, care should betaken to select the correct glass. Old glass can be
fragile and care needs to be taken when removing it from a frame. The 19th
century method of removing valuable old glass from its Georgian sash, was to
dump frame and glass in a heap of farmyard manure for 6-8weeks. The glass was
alleged to fall out easily! However, today a system exists using infrared
technology to soften the putty without heating the glass - it is also relatively
less odorous! It is sometimes possible for a good glass cutter to cut old glass
to a new size, provided it was well made originally. Old glass may have
discoloration or surface degradation due to exposure and too high an alkali
content in the original composition. Unfortunately, such damage is irreversible.
WEIGHTS AND QUANTITIES
These may conflict with information gleaned by other researchers, as measures and quantities seem to have varied at different periods (and possibly in different places).
- Crib: a hundredweight or 150 sq feet. Case: 24 leaves, half cases also sold, of 12 leaves.
- Neve a case ranged from 25 tables (French glass) to 45 of Newcastle. This dependent on diameter of the table: those 5 square foot were 45 to the case, at 6 square foot there were 35.
- Table or leaf: each unit of glass, uncut, e.g. circles, or segmentally headed rec- tangles in broad glass. According to Neve, tables of crown were 3 ft 6 in or 3 ft 8 in, giving area of 9-10 ft2. The case then had a quantity of 220-240 ft2. Tables of crown became larger during the 18th century, measuring up to 5 ft and 6 ft in diameter.
- Webb or way: this peculiar term to describe a quantity of glass seems to have been applied only in regard to Rhenish glass. Each webb consisted of bunches of six glass plates of about two square foot. At the end of the 17th century there were 100 bunches per webb, but later 60 was the usual amount.
- Squares: the common term to describe a rectangular pane of glass in timber casements or sashes. Very often building accounts only mention the term without giving exact sizes. Sometimes this is elaborated upon the general sizes being from 6in by 8in upwards, with l9in by 12 in and 12 in by 16 in usual. Though most 244 panes were rectangular, square ones are also found.
- Quarries: Neve gives details about calculating sizes of quarries, and the standards used, which would be of relevance to anyone needing to calculate exact measurements but are not necessary here. Suffice to mention that there were two types, ordinary and long, and that the most usual size was 12s (meaning that there are 12 of l2s in a foot of glass); these are 6 in long by 4 in wide.
- Measuring glass according to weight: Neve quotes a Mr Leybourn as stating that 225 ft of glass equals about 200 lb, i.e. 9 ft is about 8 lb weight. In an article which mentioned that the chapel in Dublin Castle bought 600 lb of glass in the late 14th century, the author quotes the then (1920s) clerk of works at York Minsteras estimating 3 lb per foot of glass. The discrepancy is interesting and may be explained by extreme thinness of good crown, which weighs less per foot.
It is hoped that this short explanation of types and terms may be of some use to those who come into contact with this most aesthetic of materials. I am very interested in any other information on this subject, or others linked to it, if anyone has snippets or knows of obscure sources that I may have missed.
Nessa Roche is based in Dublin
Glass Types and Measures http://ihbc.org.uk/context_archive/48/glasstypes_dir/glasstypes_s2.htm