Sheet Glass is first blown in the form of a large hollow cylinder. The ends of the cylinder are then cut off, and it is split down one side with a diamond, after which it is placed in a flattening kiln, where, under the influence of heat, it opens out into a flat sheet, which is carefully annealed and then cooled very gradually.
The qualities of sheet glass are as follows, and may be used for the purposes mentioned : -
A. For pictures (the best).
B. Do. (ordinary).
Best. For the best glazing in first-class dwelling-houses.
Seconds. Good glazing.
Thirds. Ordinary glazing.
Fourths. Coarse. Unfit for most purposes. The supply is limited.
The different classes may be used for the same purposes as the corresponding qualities of crown glass, as given above, but are available for large panes.
Thickness in inches.
Every 1/16 inch adds 13 oz. to the weight per foot superficial.
The largest sizes which, for all practical purposes, are made in the various substances of sheet glass are as follows : -
Weight per foot superficial in ounces.
Maximum length. Inches.
Maximum width. Inches.
Maximum area in feet superficial.
It will be understood that the size is governed by the maximum area. A sheet may be of the maximum length or of the maximum breadth, but no combination of length and breadth must exceed the area given in the last column.
The usual stock sizes of sheet glass are from 48 inches x 34 inches up to 50 inches x 36 inches. Any size above these comes under a special tariff of prices.
The variation of price, according to weight per foot superficial and size, is given in the ordinary builder's Price Books.
Sheet glass is generally sold in crates. The number of sheets in a crate varies according to the thickness of the glass, and is as follows : -
15 oz. glass..
of stock sizes.
21 „ .
26 „ . . .
Sheet glass has a somewhat duller surface than crown glass, but can be made thicker and to yield larger panes.
Cylinder Glass, German Plate Glass, and British Sheet Glass, are various names given to sheet glass.
Fluted Sheet Glass is of a wavy section, having flutes or corrugations on both sides.
The sizes kept in stock do not exceed 13 feet in area, or 55 inches in length, or 38 inches in width. It is not advisable to make fluted sheets larger than this, but, if ordered, they can be made of the same size as ordinary sheets.
1 This glass, though sold as 15 oz., generally weighs 16 oz. per foot superficial, and is 1/12 inch in thickness.
This glass is used in situations where it is necessary to secure privacy, without so much obstruction to light as is offered by obscured glass.