The glazing of windows originally belonged to the painters' trade, and when glass has been broken it is still customary to go to a painter to get it replaced, but when new windows are to be glazed it is so much more convenient to glaze them at the mill or factory where the sash are made that this has now, the author believes, become the universal custom, and hence the glass and glazing is usually included in the carpenter's specifications.
Common window glass is almost always set with putty and secured with triangular pieces of zinc called glaziers' points, driven into the wood over the glass and covered by the putty. In the best work a thin layer of putty is first put in the rebate of the sash, the glass placed on it and pushed down to a solid bearing. This is called "back puttying." The points are then driven about 8 or 10 inches apart, and the putty applied over the glass and points so as to fill the rebate. Outside windows should always be glazed on the outside of the sash. Plate glass should be back puttied and secured by wooden beads, and also all door lights.
Leaded glass is generally furnished and set by parties that make a business of ornamental or "stained" glass. It is quite common for the architect to fix a certain sum of money, in the specifications, to be allowed by the carpenter for the leaded glass, and to be expended under the direction of the architect, although where clear glass is used it is just as well to show the pattern on the drawings and specify it in the same manner as any other work. If colored glass is to be used, however, it is best to make a definite allowance and then entrust the work to a good art glass worker.
Sheet Glass. - Common window glass is technically known as sheet or cylinder glass. "It is made by the workmen dipping a tube with an enlarged end in the molten glass or 'metal' until from 7 to 10 pounds are gathered up. Then it is blown out slightly, taken on a blowing tube and still further manipulated, until a cylinder about 15 inches in diameter and 45 inches long is formed. This cylinder has the two ends trimmed off, is then cut longitudinally and gradually warmed, when it is placed on a large flat stone supported by a carriage, where it is heated until it softens sufficiently to open out flat; the carriage is then pushed into the annealing chamber and the sheet taken off."
Grades and Qualities of Sheet Glass. - Sheet glass is graded as double or single strength, French, German or American make, and as first, second or third quality, the strength and quality always, affecting the price.
Previous to about the year 1875 nearly all of the window glass used in this country was imported from France or Germany, but since then American glass has been gradually taking the place of imported glass, until at the present time little, if any, imported sheet glass is used, except in the portions of the country bordering on the Atlan-. tic. In Boston, German glass is used entirely when first-quality glass is furnished, as only the second and third qualities of American glass are carried in that market (with the exception of special brands, such as Chambers' " Eagle Brand "). The German glass, so called, sold in the Eastern markets is really made in Belgium, but is still sold under the old name. There is now no true French or German sheet glass carried in this country, and when either are specified Belgium or American glass is furnished.
The Belgium glass is generally considered as superior to the American glass, but it is very doubtful if there is any practical difference between the two in the better grades. Since the adoption of the new tariff the price of German glass in the Eastern cities is about the same as that of American glass.
All common sheet glass, without regard to quality, is graded according to thickness, as "single strength" or "double strength." The double-strength glass is supposed to have a nearly uniform thickness of \ inch, while the single-strength may be as thin as 1/16 inch. The thickness of single-strength glass, however, is generally far from uniform.
All lights over 24 inches wide should be double strength, and in the better class of buildings it is best not to use single-strength glass at all.
Both single and double-strength glass are sorted into three grades or qualities, the classification depending upon color, brilliancy and flaws.
In the common American glass the best quality is designated as AA, the second as A and the third as B. The AA quality is supposed to be as good glass as can be made by the cylinder process. As even this glass, however, is not entirely free from defects, it is very difficult for any one but an expert to tell exactly whether certain lights of glass are first or second quality. The second and third qualities are only suitable for cellar windows, stables, factories, con* servatories, etc. For residences, schools, apartment buildings, etc., nothing poorer than first quality should be specified.
Sizes. - The regular stock sizes vary by inches from 6 to 16 inches, and above that by even inches up to 60 inches in width and 70 inches in height tor double strength and 30x50 inches for single strength.
Cost. - The prices for sheet glass, as for all other clear glass, varies with the size, strength and quality. It is determined by a schedule, or price list, fixed from time to time by the glass companies, from which a very large discount is made, fluctuations in prices being regulated by the discount, the list generally remaining unchanged for a number of years. The only way of ascertaining the price of a light of glass of a given size is by means of the price list and discount.
The price per square foot increases rapidly as the size of the glass increases, so that it is much cheaper to divide a large window into eight or twelve lights than into two lights. Compared with the cost of the building, however, the glass is a small item, and in the better class of buildings each sash is usually glazed with a single light of glass. In factories, workshops, etc., where there is usually a great amount of glass surface, the size of the lights is not of so much importance, while the saving by using small lights is quite an item ; hence twelve and even sixteen-light windows are generally used in such buildings.
The following table shows quite clearly the relative cost per square foot for different sizes of American glass, the prices given being about an average for the whole country at the present time (1897):
SIZE OF LIGHT IN INCHES.
10 X 12
PRICE IN CENTS.
From this table it can be seen that to glaze a given area with 10x12-inch lights will cost only one-half what it would with 30x36-inch lights, and only about one-third the cost of 40x60-inch lights. Two lights 30x70 inches cost but little more than half as much as one light 60x70 inches. Two lights of glass of the same area but different dimensions, however, will cost practically the same.
The comparative cost of German and American sheet glass is indicated by the table in Section 104.
Special Brands of Sheet Glass. - There are a few American firms that make a better quality of sheet glass than that which is ordinarily found in the market, and they designate their product by special trade marks.
One of these special brands of common window glass is "Chambers' Eagle Brand," which is made in three qualities, designated as "Three Star," "Two Star" and "Star," and in both single and double strength. The Three Star, double strength, is claimed to be superior to the ordinary AA glass, and it has this advantage, which most architects will appreciate, that each sheet bears a label showing the brand and quality. This enables the architect to be sure that he is getting the kind of glass specified. The cost of this glass is practically the same as that of ordinary American glass of corresponding grade.
The Chambers Glass Co. also make a special grade of window glass known as " Chambers' Eagle Brand " 26-ounce crystal sheet glass.
This glass is made by the cylinder process, but under improved methods ; it is a little thicker than the double-strength glass and of greater brilliancy and transparency. This is probably the best glass made, next to plate glass, and either it or plate glass should be specified for all first-class residences, hotels, office buildings, etc. For ordinary sizes it costs about 90 per cent. more than first quality double strength and about one-half as much as plate glass. It is made in regular sizes up to 48x52 inches, and each sheet is labeled with the trade mark. There are also other brands of "crystal sheet" glass, which are of about the same quality.
Defects of Sheet Glass. - All sheet glass, when looked upon from the outside, has a wavy, watery appearance, like the surface of a lake slightly agitated by the wind, and when the sunshine falls upon it the irregularity of the surface is greatly emphasized. This characteristic of sheet glass is due to its being made in the shape of a cylinder and then stretched or flattened out into a sheet, and cannot be wholly avoided. Besides this universal defect, the cheaper grades are often stringy or blistery, or sulphured, or smoked, or stained, so that, in looking through the glass, objects seen at a distance are deformed and distorted.
I04. Plate Glass. - For lights of glass over 60x70 inches in size it is necessary to use plate glass, and owing to the watery and uneven appearance of cylinder glass, plate glass, which is perfectly clear and transparent, is becoming more largely used every year for windows of ordinary size, especially in fine residences, hotels and office buildings.
The process of manufacture of plate glass is entirely different from that of sheet glass. In making plate glass the metal, which is prepared with great care, is melted in large pots and then cast on a perfectly flat cast iron table. "The width and thickness of the plate is determined by means of metal strips called 'guns,' which are fastened on, and on which a heavy metal roller travels. The ends of the guns are tapered, so that when the roller is at one extremity it and the guns form three sides of a shallow rectangular dish. The molten metal is poured on and the roller passed along slowly, forcing the metal in front of it and rolling out the sheet."
"For polished plate the rough plate is carefully examined for flaws, which are cut out, leaving the largest size sheet practicable ; then the plate is fastened to a revolving stone by means of plaster of Paris, and two heavy shoes, shod with cast iron, are mounted over it. The stone is then revolved and sand and water fed on to the surface; the shoes revolve also, going over all parts of the plate and grinding it down to a true plane. Then emery powder is fed on in successive degrees of fineness until the plate is made absolutely smooth and all grit removed. Then new rubbers, shod with very fine felt, are put on and liquid rouge is added for the polishing. When one side is completed the other side is similarly treated, the plate losing about 40 per cent. in weight by the operation."
Qualities of Polished Plate Glass. - There are practically but three qualities of polished plate glass now on the American market, viz.: French plate and two grades of American plate - first, silvering quality, which is used for mirrors exclusively, and second, glazing quality.
French plate is now only used in this country for mirrors, for which purpose it is generally considered superior to the American glass, although the silvering quality American glass is rapidly supplanting the French glass, and the manufacturers claim it to be equal to the latter in every respect.
French plate may be distinguished from American plate by the color when looked at endways, the French glass showing perfectly clear and white, while the American, glass has a decidedly bluish color. American glass is said to resist the weather better than the French glass.
The usual thickness of American polished plate glass is ¼ inch, but there is also made a thinner plate, commonly known as 3/16-inch plate, which is just like the regular glazing plate, except that it is thinner. It is ground from the same thickness of rough plate as regular plate glass. It is used principally in thin sash, such as are used in railway coaches, and where the saving in weight is a consideration.
American glazing plate glass is made in but one quality, the only variation being in the thickness.
Cost. - The cost of plate glass varies with the size of the lights, but not to so great an extent as with sheet glass. At the present time the net price of American polished plate, glazing quality, is about 48 cents per square foot up to 10 square feet; 66 cents from 10 to 40 square feet, and 80 cents for sheets containing 120 square feet. For larger sheets the price increases rapidly up to $2.50 per square foot for the largest size.
The price, however, can only be accurately determined by means of the official price list and the discount, which at present varies from
75 to 80 per cent, according to locality. Three-sixteenths-inch plate costs from 10 to 15 per cent, more than the regular plate, because of the extra expense in grinding it down. French plate costs about 50 per cent. more than the American plate.
Sizes, - Glazing plate is made in stock sizes varying by even numbers from 6x6 inches up to 144x200 inches, or 138x208 inches.
Comparative Cost of Different Kinds of Window
Glass.* - The following table gives as close an idea of the comparative cost of the different kinds and qualities of glass used in this country for glazing as it is possible to arrive at, the prices for the sizes given being the present net average price :
KIND OF GLASS.
SIZE OF LIGHT IN INCHES.
26-ounce crystal sheet..........
German (Belgium) Sheet.
Double strength, 1st quality........
" " 2d quality........
Double strength, 1st quality........
" " 2d quality........
Single strength, 1st quality........
" " 2d quality........
It will be seen from this table that the relative difference in the cost of plate and sheet glass decreases rapidly as the size of the light increases.