Glass is cut with either a diamond or a tiny sharp-edged and very hard steel wheel. The diamond is undoubtedly the finer tool, especially for thick glass. But a glaziers diamond costs a pound or more, whereas a first-class steel-wheel cutter can be bought for a shilling or eighteenpence, including a few spare wheels. In the hands of an expert the wheel gives excellent results; and most of the worlds glass-cutting is done with wheels. A wheel cutter must be kept well lubricated to do itself full justice.
The beginner is advised to get his hand in by practising on waste pieces of glass before attempting serious cutting.
The glass to be cut must be supported by an absolutely flat surface as large as, or larger than, itself – a drawing-board or a table. For cutting straight lines the tool must be guided by a straight-edge thick enough to prevent the tool climbing on to it. The straight-edge must be half the width of the head of the tool away from the marks to allow cutting through the marks.
The tool is held with the handle passing between first and second fingers, which press on the front, while the thumb presses on the back. A diamond cuts best when the handle tilts backwards at a particular angle, which can be found only by experience. If the tool is then properly used it cuts with a silky sound and makes a hardly visible scratch. A rough scratch means that the angle is wrong or the pressure too great.
The cut should be made right acres. from close to the beginning edge. A wheel will need more pressure than a diamond; but avoid scoring the glass; and on no account go over the cut again, if dissatisfied with its appearance.
So far only the surface of the glass has been affected. But the scratch is converted into a crack right through if the glass is bent away from it. Thin glass separates readily enough. Large pieces should be laid with the cut just beyond the edge of the support and broken by a push. Thick glass may prove stubborn; in which case the glass is tapped smartly on back, at the centre of cut, until cracking begins. The crack may then be extended in both directions by more rapping.
If much cutting has to be done, it will pay to rule the board in both directions with fines dividing its surface in J-inch squares, the inch lines being marked more boldly than the others. The fines will be visible through the glass and do away with the need for marking the glass when measuring, besides assisting in getting the corners square.
First-class joints can be made only with good glue, freshly prepared. The best glue is Scotch. Glue that will absorb twice or more times its own weight of water is good glue. Whether it does so can easily be tested by weighing a given quantity of it before and after a long soaking.
When the glue has been swelled into a jelly, it is transferred to a glue-pot fitting into an outer pot containing water, and heated for an hour or so, any scum being removed as it forms. Glue of the