HISTO RICAL

One of the earliest of all Diamond tools introduced to the world was the glazier's Diamond, for use for the cutting and shaping of glass plate, both for windows and for mirrors. We shall begin with the description of this slow, almost personal early tool, and progress later towards those high­speed modern machine tools which are basic in many engineer­ing mass-production lines today. The glazier's Diamond is used not only for cutting plates for windows, but also for numerous subsidiary uses such as the cutting of hard glaze tiles, dividing of tubes, making special glass shapes, and so on.

Today in modern architecture sheet glass is playing a domi­nant part and, of course, such glass has to be cut to size. This is best done by using the glazier's Diamond, and since this ancient tool now plays its slight yet still essential part in the building industry we shall first briefly review the evolution of this glazier's cutting tool. In spite of mechanisation it is still often used as a hand tool by the expert.

The glazier's Diamond is one of the oldest of all Diamond tools. There is no doubt at all that from earliest times the sharp point of a Diamond has been used for scribing and engraving. The examination of some ancient jewels shows that fine cuts on them have very probably been made with Diamond. There exists a manuscript dated about 400 years after Pliny which describes the engraving of stone with splin­ters broken off Diamonds. The art of engraving with Diamond persisted, and in Europe it reached considerable aesthetic achievement by the 16th century, from which time on vessels of glass were often artistically engraved. It would not be sur­prising to expect that some glass engraver accidentally dis covered the art of glass-cutting with a Diamond. There exists a detailed description in a manuscript dated about 1425 which says that to cut a sheet of glass draw a fissure on it with a line Diamond and then tap the sheet under water, whereupon it will break along that line drawn by the Diamond.

Although this use of the Diamond as a cutter was recorded over 500 years ago, it was not until the mid 18th century that the glazier's Diamond became an industrial proposition. Indeed, it was only after the invention by Shaw, in England in 1814, of the familiar swivel-head mounting that the glazier's Diamond came into widespread popular use. In earlier times glass was cut either with an emerald or indeed a fissure was led along slowly by application of a hot iron, but neither method at all compares with the excellence of the Diamond cutting tool for parting glass sheet.

It is to be noted that even today the best Diamond glass-cutting tools are small natural Diamonds, and not polished or shaped Diamonds. Truth to tell, the past 150 years has seen hardly any advance or improvement in the glazier's Diamond cutter. For cutting glass a small Diamond is selected (it may even only weigh 1/100 part of a Carat) and this is soldered into a brass or a steel mount. Many octahedron Diamonds have curved faces, and where two adjacent such faces meet there is an extremely sharp and very hard curved edge. This is the edge used to cut the glass. It is applied to the sheet and only mild pressure exerted. The direction of cut is critical. Should too much pressure be applied, a rough scratch results. If the ml is correctly made, the Diamond 'sings' as it moves, induc­ing as it moves along its path, in depth, a fine fissure. With a sharp snapping action the sheet can be broken along the fissure. A good deal of practice is required, but in the hands of an expert failures are extremely rare.