Glass—With Care

Auckland Star, Volume LXXII, Issue 86, 12 April 1941, Page 16 (Supplement)

Glass —With Care

"THE Egyptians are believed to have invented glass about 4000 B.C. But the art of making it may have been lost, because archaeologists say that the glass ur>ed in Egypt was imported from Syria. This kind of glass was opaque, and v.ii used for making ornaments and beni'.a and for decorative purposes and drii.king vessels. It was not until the C hiistian era thnt glass-blowing through an iron tube was invented. From that point its manufacture spread rapidly throughout "Europe, and bv A.D. 200 most countries had their iiwll glass industries. (ibss i 3 made principally of silica, .variably used in the fortn of sand, ■lie of the finest sands with a high .1 content come from the forest of linebleau in France, from Germany I'elgium. ' itain has large deposits at King's ..it, but these have a comparatively _!i content of iron oxide—.os per cent i • be exact—and therefore they are not iliable for the manufacture of the very

finest glass. Too much iron oxide makes tlie glass green. Silica sand is mixed with soda, potash, lime and red lead, the fundamental materials. Other ingredients may be added, such as 'decolorising agents to make the glass opaque. Once the mixture has been heated to a molten state, it is treated in various ways to produce different kinds of glass. Ordinary window glass is "drawn" cither straight ir/.-> sheets or !:ito cylinders, which are cut and then flattened in special presses. Plate glass its rolled into enormotis sheets, which are afterwards cut and polished. For domestic and "thick-walled" glass goods the molten mixture is poured into moulds, after which the goods go through various polishing and finishing processes. A good deal of this cheap "pressed" glass used to come from Czechoslovakia before the war.

By Clement Yorke

"Cut" glass, used for ornaments and for better types of drinking glasses. is the product of a very highly skilled operation. Once the rough shape has been formed, the pattern is chalked on and roughly cut on a rotating ,;nn wheel with a trin ng lar edge. Sand and water are poured on the wheel as it comes in contact with the glass, and it is the sand which actually does the cutting. You can see right through glass because the molecules < ' which it is c«nposed are so spaced out in the substance as to allow the rays of light to pass between them. Glass manufacturers use a large percentage of broken glass in their furnaces. Sometimes as much as SO per cent of the mixture will be broken glass, or

"cutlets," as the trade calls it. All the glass which has been shattered by bombs will be sort"' ded and used again, so that it is really a non-waste product.

It is, of course, impossible to estimate how iniK-h glass is likely to be broken in air raids, hut in Madrid more than 1,000.000 panes were needed to repair the damage done during the defence of the city.

Glass grows fragile with advancing

age. Continued vibrations and reception of •'musical"' noi.-.cs—not audible to the human ear—make minute holes in the glass.

This is particularly so in the ease of old church lights. With the passing of years the holes deepen and eventually the glass flakes completely away.

The thickest glass when it is smashed breaks into far many more pieces than thin glass, which by comparison is much the stronger.

Stained glass was an industry of great importance at; «ne time, and it is only in recent years that many of the different methods of manufacture have been rediscovered.

Xo manufacturer has done more for the stained glass industry than the firm of James Powell. The Powells took over the Whitefriars works in the early part of the last century and their research helped to re-establish a stained glass trade.

"Safety" Accident Accidents caused through flying glass gave the inspiration to the French chemist who invented safety glass. Although a form of safety glass had been made in the late OO's it did not reach commercial development. Actuallv, the first pate: t for imsplintercd glass was filed in 1910.

It was in 1!)0:? that Kdouard Bcnedictus, a French chemist, dropped a bottle in his laboratory, but although it broke it did not splinter. He found from his records that 1"> years before the bottle had contained a mixture which had evaporated and left a coating inside of celluloid-like enamel of high tensile strength.

Benedictus thought no more of this until he read of an accident in which two young women wore injured by broken glass. Then he invented his safety glass—a glass "sandwich"—two pieces of glass with a sheet of celluloid in I t ween. Bern-'- - of this triple compi ion he called it "Triplex."

This new glass did not catch on until, in 1027, Henry Ford was the victim of a motor car accident. Within six months every Ford car leaving his factory was lit ted with the new safety glass.

Since 1037 it has been compulsory by law for every car used in Britain to have safety glass windscreens.

Four years ago Imperial Chemical Industries discovered a new type of "glass," made from a mixture of coal, air, and water, which they called "P pcx."' Its peculiar property was that it was not affected by ultra-violet ra vs.

It had been found that the windscreens of aeroplanes flying at great altitudes became discoloured as a result of the action of ultra-violet rays and went opaque. The new "Perspex" is now widely used in aircraft production. The "One-glass" Man

The "balloon" glass in which brandy is served originated through a doctor ordering a patient to reduce his drinking to one glass per day. A glass manufacturer friend took pity on him and the result was the '"balloon," which will hold a full-sized bottle of champagne.

Modern shop window-fronts Aiave been designed to make the gla«s invisible so that there is 110 reflection which might prevent you from seeing the goods in the window.

This lia,s been done by introducing concave shop window fronts. Another way of making glass as good as invisible is to coat it with a film of liquid soap almut for-millionths of an inch thick.

In trying to find a glass which would preserve the natural colour of .'>2 jams and fruits, the research department of a preserve manufacturing company discovered that Hies do not like yellow light. All the windows in the firm's factories were thereupon tinted yellow.