Читать книгу Stained Glass Work: A text-book for students and workers in glass - Christopher Whall - Страница 5

Cutting (elementary)—The Diamond—The Wheel—Sharpening—How to Cut—Amount of Force– The Beginner's Mistake—Tapping—Possible and Impossible Cuts—"Grozeing"—Defects of the Wheel—The Actual Nature of a "Cut" in Glass.

No written directions can teach the use of the diamond; it is as sensitive to the hand as the string of a violin, and a good workman feels with a most delicate touch exactly where the cutting edge is, and uses his tool accordingly. Every apprentice counts on spoiling a guinea diamond in the learning, which will take him from one to two years.

Most cutters now use the wheel, of which illustrations are given (figs. 1 and 2).

Figs. 1 and 2.

The wheels themselves are good things, and cut as well as the diamond, in some respects almost better; but many of the handles are very unsatisfactory. From some of them indeed one might suppose, if such a thing were conceivable, that the maker knew nothing of the use of the tool.

For it is held thus (fig. 5), the pressure of the forefinger both guiding the cut and supplying force for it: and they give you an edge to press on (fig. 1) instead of a surface! In some other patterns, indeed, they do give you the desired surface, but the tool is so thin that there is nothing to grip. What ought to be done is to reproduce the shape of the old wooden handle of the diamond proper (figs. 3 and 4).

Figs. 3 and 4.

The foregoing passage must, however, be amplified and modified, but this I will do further on, for you will understand the reasons better if I insert it after what I had written further with regard to the cutting of glass.

How to Sharpen the Wheel Cutter.—The right way to do this is difficult to describe in writing. You must, first of all, grind down the "shoulders" of the tool, through which the pivot of the wheel goes, for they are made so large that the wheel cannot reach the stone (fig. 6), and must be reduced (fig. 7). Then, after first oiling the pivot so that the wheel may run easily, you must hold the tool as shown in fig. 8, and rub it swiftly up and down the stone. The angle at which the wheel should rest on the stone is shown in fig. 9. You will see that the angle at which the wheel meets the stone is a little blunter than the angle of the side of the wheel itself. You do not want to make the tool too sharp, otherwise you will risk breaking down the edge, when the wheel will cease to be truly circular, and when that occurs it is absolutely useless. The same thing will happen if the wheel is checked in its revolution while sharpening, and therefore the pivot must be kept oiled both for cutting and sharpening.

Fig. 5.

It is a curious fact to notice that the tool, be it wheel or diamond, that is too sharp is not, in practice, found to make so good a cut as one that is less sharp; it scratches the glass and throws up a line of splinters.

Figs. 6 and 7.

Fig. 8.

How to Cut Glass.—Hold the cutter as shown in the illustration (fig. 5), a little sloping towards you, but perfectly upright laterally; draw it towards you, hard enough to make it just bite the glass. If it leaves a mark you can hardly see it is a good cut (fig. 10b), but if it scratches a white line, throwing up glass-dust as it goes, either the tool is faulty, or you are pressing too hard, or you are applying the pressure to the wheel unevenly and at an angle to the direction of the cut (fig. 10a). Not that you can make the wheel move sideways in the cut actually; it will keep itself straight as a ploughshare keeps in its furrow, but it will press sideways, and so break down the edges of the furrow, while if you exaggerate this enough it will actually leave the furrow, and, ceasing to cut, will "skid" aside over the glass. As to pressure, all cutters begin by pressing much too hard; the tool having started biting, it should be kept only just biting while drawn along. The cut should be almost noiseless. You think you're not cutting because you don't hear it grate, but hold the glass sideways to the light and you will see the silver line quite continuous.

Having made your cut, take the glass up; hold it as in fig. 11, press downward with the thumbs and upward with the fingers, and the glass will come apart.

Fig. 9.

Fig. 10, a and b

Fig. 11.

But you want to cut shaped pieces as well as straight. You cannot break these directly the cut is made, but, holding the glass as in fig. 12, and pressing it firmly with the left thumb, jerk the tool up by little, sharp jerks of the fingers only, so as to tap along the underside of your cut. You will see a little silver line spring along the cut, showing that the glass is dividing; and when that silver line has sprung from end to end, a gentle pressure will bring the glass apart.

Fig. 12.

This upward jerk must be sharp and swift, but must be calculated so as only just to reach the glass, being checked just at the right point, as one hammers a nail when one does not want to stir the work into which the nail is driven. A pushing stroke, a blow that would go much further if the glass were not there, is no use; and for this reason neither the elbow nor the hand must move; the knuckles are the hinge upon which the stroke revolves.

But you can only cut certain shapes—for instance, you cannot cut a wedge-shaped gap out of a piece of glass (fig. 13); however tenderly you handle it, it will split at point A. The nearest you can go to it is a curve; and the deeper the curve the more difficult it is to get the piece out. In fig. 14 A is an average easy curve, B a difficult one, C impossible, except by "groseing" or "grozeing" as cutters call it; that is, after the cut is made, setting to work to patiently bite the piece out with pliers (fig. 15).

Fig. 15.

Now, further, you must understand that you must not cut round all the sides of a shaped piece of glass at once; indeed, you must only cut one side at a time, and draw your cut right up to the edge of the glass, and break away the whole piece which contains the side you are cutting before you go on to another.

Thus, in fig. 16, suppose the shaded portion to be the shape that you wish to cut out of the piece of glass, A, B, C, D. You must lay your gauge anglewise down upon the piece. Do not try to get the sides parallel to the shapes of your gauge, for that makes it much more difficult; angular pieces break off the easiest.

Fig. 16.

Now, then, cut the most difficult piece first. That marked 1. Perhaps you will not cut it quite true; but, if not, then shift the gauge slightly on to another part of the curve, and very likely it may fit that better and so come true.

Then follow with one of those marked 2 or 3. Probably it would be safest to cut the larger and more difficult piece first, and get both the curved cuts right by your gauge; then you can be quite sure of getting the very easy small bit off quite truly, to fit into its place with both of them. Go on with 4, and then with one of those marked 5 or 6. Probably it would still be best to cut the curved piece first, unless you think that shortening it by cutting off the small corner-piece first will make the curved cut easier by making it shorter.

In any case you must only cut one side at a time, and break it away before you make the cut for another side.

Take care that you do not go back in your cut. You must try and make it quite continuous onwards; for if you go back in the cut, where your tool has already thrown up splinters, it will spoil your tool and spoil your cut also.

Difficult curves, that it is only just possible to get out by groseing, ought never to be resorted to, except for some very sufficient reason. A cartoonist who knows the craft will avoid setting such tasks to the cutter; but, unfortunately, many cartoonists do not know the craft. If people were taught the complete craft as they should be, this book would not have been written.

Here let me say that we cannot possibly within the narrow limits of it go thoroughly into all the very wide range of subjects connected with glass—the chemistry, the permanence, the purity of materials. With the exception of the practice of the craft, probably we shall not be able to go thoroughly into any one of them; but I shall endeavour to mention them all, and to do so sufficiently to indicate the directions in which work and research and experiment may be made, for they are all three much needed in several directions.

It becomes, for instance, now my task, in modifying the passage some pages back as I promised, to go into one of these subjects in the light of inquiries made since the passage in question was written; and I let it for the time being stand just as it was, without the additional information, because it gives a picture of how such things crop up and of the way in which such investigations may be made, and of how useful and pleasant they may be.

Here then let us have—

A LITTLE DISSERTATION UPON CUTTING

Through the agent for the wheel-cutter in England I communicated with the maker and inventor in America, and told him of our difficulties and perplexities over here, and chiefly with regard to two points. First, the awkwardness of the handle, which causes the glaziers here to use the tool bound round with wadding, or enclosed in a bit of india-rubber pipe; and, secondly, the bluntness of the "jaws" which hold the wheel, and which must be ground down (and are in universal practice ground down), before the tool can be sharpened.

His reply called attention to a number of different patterns of handle, the existence of which, I think, is not generally known, in England at any rate, and some of which seem to more or less meet the difficulties we experience, most of them also being made with malleable iron handles, so that fresh cutting-wheels can be inserted in the same handle. His letter also entered into the question of the actual dynamics of "cutting," maintaining, I think rightly, that a "cut" is made by the edge of the wheel (this not being very sharp) forcing the particles of the glass down into the mass of it by pressure.

With regard to the old-fashioned pattern of tool which we chiefly use in this country, the very sufficient explanation is that they continue to make it because we continue to demand it, a circumstance which, as he declares, is a mystery to the inventor himself! Nevertheless, as we do so, and, in spite of the variety of newer tools on the market, still go on grinding down the jaws of our favourite, and wrapping round the handle with cotton-wool, let us try and put this matter straight, and compare our requirements with the advantages offered us.

There are three chief points to be cleared up. (1) The actual nature of a "cut" in glass; (2) the question of sharpening the tool and grinding down of the jaws to do so; and (3) the "mystery" of our preference for a particular tool, although we all confess its awkwardness by the means we take to modify it.

(1) With regard, then, to the nature of a "cut" in glass I am disposed entirely to agree with the theory put forward by the inventor of the wheel, which an examination of the cuts under the microscope, or even a 6 diameter lens, certainly also tends to confirm.

What happens appears to my non-scientific eyes to be this.

Glass is one of the most fissile or "splittable" of all materials; but it is so just in the same way that ice is, and just in the opposite way to that in which slate or talc is.

Slate or talc splits easily into thin layers or laminæ, because it already lies in such layers, and these will come apart when the force is applied between them: but it will only split into the laminæ of which it already is composed, and along the line of the fissures which already exist between them.

Glass, on the contrary (and the same is true of ice, or for that matter of currant-jelly and such like things), appears to be a substance which is the same in all directions, or nearly so, and therefore as liable to split in one direction as in another, and is so loosely held together that, once a splitting force is applied, the crack spreads very rapidly and easily, and therefore smoothly and in straight lines and in even planes.

The diamond, or the wheel-cutter, is such a force. Being pressed on to the surface, it forces down the particles, and these start a series of small vertical splits, sometimes nearly through the whole thickness of the glass, though invisibly so until the glass is separated. And mark, that it is the starting of the splits that is the important thing; there is no object in making them deep, it is only wasted force; they will continue to split of themselves if encouraged in the proper way (see Plates IX. and X.). Try this as follows.

Take a bit of glass, say 3 inches by 2, and make the very smallest dint you can in it, in the middle of the narrowest dimension. You cannot make one so small that the glass will hold together if you try to break it across. It will break across in a straight line, springing from each end of the tiny cut. The cut may be only 1/8 of an inch long; less—it may be only 1/16, 1/32—as small as you will, the glass will break across just the same.

Why?

Because the cut has started it splitting at each end; and the material being the same all through, the split will go straight on in the direction in which it has started; there is nothing to turn it aside.

So also the pressure of the wheel starts a continuous split, or series of splits, downwards, into the thickness of the glass. No matter how small a distance these go in, the glass will come asunder directly pressure is applied.

Now, if you press too hard in cutting, another thing takes place.

Imagine a quantity of roofing-slates piled flat one on top of another, all the piles being of equal height and arranged in two rows, side by side, so close that the edges of the slates in one row touch the edges of those in the other row, along a central line.

Wheel a wheelbarrow along that line over the edges of both.

What would happen?

The top layer of slates would all come cocking their outer edges up as the barrow passed over their inner ones, would they not?

Now, just so, if you press hard on your glass-cutting wheel, it will press down the edges of the groove, and though there are no layers already made in the glass, the pressure will split off a thin layer from the top surface of the glass on each side in flakes as it goes along (Plate X., d, e).

This is what gives the noise of the cut, c-r-r-r-r-r-; and as the thing is no use the noise is no use; like a good many other things in life, the less noise the better work, much cry generally meaning little wool, as the man found out who shaved the pig.

But the wheel or the diamond is not quite the same as the wheel of the wheelbarrow, for it has a wedge-shaped edge. Imagine a barrow with such a wheel; what then would happen to your slates? besides being cocked up by the wheel, they would also be pushed out, surely?

This happens in glass. You must not imagine that glass is a rigid thing; it is very elastic, and the wedge-like pressure of the wheel pushes it out just as the keel of a boat pushes the water aside in ripples (Plate X., d, e).

All these observations seem to me to bear out the theory of the inventor, and perhaps to some extent to explain it. I am much tempted to carry them further, and ask the questions, why a penknife as well as a wheel will not make a cut in glass, but will make a perfectly definite scratch on it if the glass is placed under water? and why this line so made will yet not serve for separating the glass? and why a piece of glass can be cut in two (roughly, to be sure, but still cut in two) with a pair of scissors under water, a thing otherwise quite impossible?

But I do not think that the knowledge of these questions will help the reader to do better stained-glass windows, and therefore I will not pursue them.

(2) The question of sharpening the tool is soon disposed of.

If the tool is to be sharpened, the jaws must be ground down, whether the maker grinds them down originally or whether we do it. Is sharpening worth while, since the tool only costs a few pence?

Well, it's a question each must decide for himself; but I will just answer two small difficulties which affect the matter.

If grinding the jaws loosens the pivot, it can be hammered tight again with a punch. If sharpening wears out the oil-stone (as it undoubtedly does, and oil-stones are expensive things), a piece of fine polished Westmoreland slate will do as well, and there is no need to be chary of it. Even a piece of ground-glass with oil will do.

(3) But now as to the handle. I am first to explain the amusing "mystery" why the old pattern shown in fig. 1 still sells.

It is because the British working-man is convinced that the wheels in this handle are better quality than any others.

Is he right, or is it only an instance of his love for and faith in the thing he has got used to?

Or can it be that all workmen do not know of the existence of the other types of handle? In case this is so, I figure some (fig. 17). Or is it that the wheel for some reason runs less truly in the malleable iron than in the cast iron?

Fig. 17.

Certain it is that the whole trade here prefers these wheels, and I am bound to say that as far as my experience goes they seem to me to work better than those in other handles.

But as to all the handles themselves, I must now voice our general complaint.

(1) They are too light.

For tapping our heavy antique and slab-glasses we wish we had a heavier tool.

(2) They are too thin in the handle for comfort, at least it seems so to me.

(3) The three gashes cut out of the head of the tool decrease the weight, and if these were omitted the tool would gain. Their only use that I can conceive of is that of a very poor substitute for pliers as a "groseing" tool, if one has forgotten one's pliers. But (as Serjeant Buzfuz might say) "who does forget his pliers?"

The whole question of the handle is complicated by the fact that some cutters rest the tool on the forefinger and some on the middle finger in tapping, and that a handle the sections of which are calculated for the one will not do equally well for the other.

But the whole thing resolves itself into this, that if we could get a tool, the handle of which corresponded in all its curves, dimensions, and sections with the old-established diamond, I think we should all be glad; and if the head, wheel, and pivot were all made of the quality and material of which fig. 1 is now made, but with the handle as I describe, many of us, I think, would be still more glad; and if these remarks lead in any degree to such results, they at least of all the book will have been worth the writing, and will probably be its best claim to a white stone in Israel, as removing one more solecism from "this so-called twentieth century."

I shall now leave this subject of cutting for the present, and describe, up to about the same point, the processes of painting, taking both on to a higher stage later—as if, in fact, I were teaching a pupil; for as soon as you can cut glass well enough to cut a piece to paint on, you should learn to paint on it, and carry the two things on step by step, side by side.