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).
[Illustration: 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).
[Illustration: 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.
[Illustration: FIG. 5.]
[Illustration: FIGS. 6 and 7.]
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.
_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.
[Illustration: FIG. 8.]
[Illustration: FIG. 9.]
[Illustration: FIG. 10, A and B]
[Illustration: 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.
[Illustration: 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.
[Illustration: FIG. 13.]
[Illustration: FIG. 14.]
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).
[Illustration: 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.
[Illustration: 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 laminae, _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 laminae 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?
[Illustration: 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.