Grating

“ The latter found that certain gratings exercised a converging power upon the spectra formed upon one side, and a corresponding diverging power upon the spectra on the other side. Let us suppose that the light is incident perpendicularly, and that the grating interval increases from the centre towards that edge which lies nearest to the spectrum under observation, and decreases towards the hinder edge. ”

“ If the grating be composed of alternate transparent and opaque parts, the question may be treated by means of the general integrals (§ 3) by merely limiting the integration to the transparent parts of the aperture. ”

“ If we throw a beam of light on a grating which contains perhaps some 14,000 parallel lines in the space of one inch in width, the lines being ruled on a plane and bright metallic surface, and receive the reflected beam on a screen, the appearance that is presented is a white central spot, together with six or seven spectra of gradually diminishing brightness on each side of it, all except the first pair overlapping one another. ”

“ The most interesting phenomena of diffraction are those presented by gratings, as are technically denominated the systems of linear and very narrow openings situated parallel to one another and at very small intervals. ”

“ The number of bolts, gratings, and locks for this single courtyard would have sufficed for the safety of an entire city. Aramis was neither an imaginative nor a sensitive man; he had been somewhat of a poet in his youth, but his heart was hard and indifferent, as the heart of every man of fifty-five years of age is, who has been frequently and passionately attached to women in his lifetime, or rather who has been passionately loved by them. ”

“ Seen near, you see the drawing through the film; but as you go away the light will come pouring stronger and stronger through the brush or stipple marks on the cheeks, until all films will cut out against it like black spots, altering the whole expression past recognition.
Try this on simple terms:—
Do a face on white glass in strong outline only: step back, and the face goes to nothing; strengthen the outline till the forms are quite monstrous—the outline of the nose as broad as the bridge of it—still, at a given distance, it goes to nothing; the expression varies every step back you take. ”

“ When, therefore, the main relations of colour have been all set out and decided for your window, turn your attention to small differences, to harmonies round the harmonies. Make each note into a chord, each tint into a group of tints, not only the strong and bold, but also the subtle and tender; do not miss the value of small modifications of tint that soften brilliance into glow. Study how Nature does it on the petals of the pansy or sweet-pea. You think a pansy is purple, and there an end? ”

“ On the other hand, when falling upon a piece of glass having an irregular surface, and containing all manner of irregularities such as striæ, air-bells, and even pieces of enclosed solid matter, the light is scattered, refracted, and deflected into all manner of directions until it almost appears to emanate from the body of the glass itself, which thus appears almost to shine with an internal light of its own; the eye can hardly perceive the presence of external objects, and the whole window appears as a brilliant self-luminous object. ”

“ Ductility of Glass.—We all know, that when glass is well penetrated with the heat of the fire, the workmen can figure and manage it like soft wax; but, what is most remarkable, it may be drawn, or spun out, into threads exceedingly long and fine. Our ordinary spinners do not form their threads of silk, flax, or the like, with half the ease and expedition the glass-spinners do threads of this brittle matter. We have some of them used in plumes for children’s heads, and divers other works, much finer than any hair, and which bend and wave, like hair, with every wind. ”

“ Decorative Processes.—Majolica painting is the application of a coloured glaze rich in lead by means of a brush. Ground-laying consists in dusting powdered enamel colour on to a pattern first printed on glazed ware with an oily medium. Colour dusting differs from the same only in detail.
Aerographing (colour blowing) is the blowing on to the ware, by means of a jet of compressed air, coloured glaze, or enamel colour held in suspension in oil or other liquid in a glaze kettle or aerograph instrument. ”

“ The most frequent form of the 18th-century grate was rather high from the hearth, with a small hob on each side. The brothers Adam designed many exceedingly elegant grates in the shape of movable baskets ornamented with the paterae and acanthus leaves, the swags and festoons characteristic of their manner. The modern dog-grate is a somewhat similar basket supported upon dogs or andirons, fixed or movable. In the closing years of the 19th century a “well-grate” was invented, in which the fire burns upon the hearth, combustion being aided by an air-chamber below. ”

“ So much sickness and suffering may, we are convinced, be prevented by kindling a small fire every night and morning, that all pleasure in the beauty of fresh, pretty-colored grates and fireplaces is lost in the knowledge of the price paid for it. A well blackened grate has more attractions for us, as it speaks of dry rooms, rosy cheeks, and good health, whereas unused and spotless bricks tell of rheumatism, chills and fever, and pale, sallow faces. ”

“ The cutting and putting together of the glass is called glazing, and it is this that gives the window colour; while the enamel work is spoken of as painting, and gives detail, richness, and texture.
I shall presently show that the glazing and painting are really two separate crafts, having separate origins and development, and that stained glass as we know it, or as it should be called in strict accuracy "stained-and-painted" glass, is the product of their union. ”

“ Prepare a fire in a grate, the top bar of which will let down in a similar way to that in an ordinary kitchen grate, taking care, however, that, at the commencement of the operation, the bar is up in its place, and the grate full to the top with glowing cinders or wood embers, so that a great heat may be obtained without any flame. ”

“ You take your tracing-brush and try to mend it with a touch of pigment; and so on, and so on; till you timidly say (feeling as if you had been walking among egg-shells for the last hour) , "Well, I think it will do, and I daren't touch it any more." And supposing by these means you get a head that looks really what you wanted; the work is all what glass-painters call "rotten"; liable to flake off at the least touch; isolated [Pg 125] bits of thick crust, cut sheer out from each other, with clear glass between. ”

“ The panes of glass that let the light through ought to be hidden or veiled just as are the lamps that light theatres, then the objects can be observed without the annoyance of the sparkle of the window. ”

“ The first stroke will really frighten you; for a flash of silver light will spring along after the point of the needle, so dazzling in contrast to the extreme dark of the matt that it looks as if the plate had been cut in two, while the matt beside it becomes pitch-black by contrast. Well, you go on, and by putting more strokes, and reducing the surrounding darkness generally, you get the drawing to look grey—but you get it to look like a grey pen-drawing or etching, not like a painting at all. ”

“ Take a glass fashioned in a contrary manner to a common burning-glass, and placing it between your hand and the rays of the sun, observe whether it diminishes the heat of the sun, as a burning-glass increases and strengthens it. ”

“ In shading the face, hands, and those parts of the drapery which require it, a glass easel is used, on which the figure is put together, and the parts made to adhere by wax, so that the artist is able, while painting, to form an idea by transmitted light of the effect which will be produced when the window is finished. ”

“ The rays of larger lamps, burned either in flood or spotlight hoods, are colored with gelatine mediums, held before the light in frames of proper size. The gelatine colors also fade under heat, and, being very fragile, crack and tear, and must be frequently renewed. For durability, the best color medium is a sheet of glass with the color blown in. ”

“ Spectacle-frames with fine wire gauze in place of glass are found to answer perfectly for the protection of the eyes from dust in various trades and occupations, such as stone-cutting, thrashing, etc. Such spectacles permit the necessary access of air to the eye, and produce no inconvenience to the wearer. ”

“ But go nearer and look into the glass itself. By some malformation or mere freak of make, all the images it throws back are livid. Flood the room with sunshine; stand before this glass with youth and hot blood tingling on your cheeks; and the glass will give back neither sun nor colour; but your own face, blue and dead, and behind it a horror of inscrutable shadow. ”

“ In all the work the artist has not forgotten that the special glory of stained glass is in luminous colour, not laid on the surface, but burnt in and filling the whole substance of the glass. It is colour which no picture on which light falls can produce. ”

“ A most convincing proof that glass transmits the rays of the sun without being heated by them is afforded by the burning lens, which by converging the rays to a focus will set combustible bodies on fire, without its own temperature being raised. ”

“ The light from our glass coils produced magical effects at times, lingering on the wrinkled roughness of some natural arch, or some overhang suspended like a chandelier, which our lamps flecked with fiery sparks. ”

“ Not only would the choir be too dark, but, besides, we would lose the contrast of light against gloom that renders it so impressive in its dignity. This observation introduces another type of glazing for which we shall seek in vain after this century. If we demand more light from our clerestory and at the same time insist on [Pg 30] coloured glass, then we must use fewer strips of light-obscuring lead, which means fewer and larger pieces of glass. Thus we will obtain more illumination than is yielded by the heavily-leaded windows below. ”

“ Smooth and polished surfaces reflect light most powerfully, and send to the eye the images of the objects from which the light proceeded before reflection. Glass, which is transparent--transmitting light--would be of no use to us as a mirror, were it not first coated on one side with a metalic amalgam, which interrupts the rays in their passage from the glass into the air, and throws them either directly in the incident line, or in an oblique direction. ”

“ It is as impossible to produce the best effect from one tone or colour, as to make a melody upon one note of the harmonic scale; it is skilful variation of tone, the gradation or even judicious opposition of tint which gives exquisite satisfaction to the eye. In music, sequence produces this effect upon the ear, and in colour, juxtaposition and gradation upon the eye. Notes follow notes in melody as shade follows shade in colour. ”

“ A thin transparent Body, which is denser than its ambient Medium, exhibits more brisk and vivid Colours than that which is so much rarer; as I have particularly observed in the Air and Glass. For blowing Glass very thin at a Lamp Furnace, those Plates encompassed with Air did exhibit Colours much more vivid than those of Air made thin between two Glasses. ”

“ Burning Glasses—Ductility of Glass—Remarkable Ductility and Extensibility of Gold—Pin Making—Needles—Shoes—The Great Bell of Moscow.
Burning Glasses.—We have some extraordinary instances and surprising accounts of prodigious effects of burning-glasses. Those made of reflecting mirrors are more powerful than those made with lenses, because the rays from a mirror are reflected all to one point nearly; whereas by a lens, they are refracted to different points, and are therefore not so dense or ardent. ”

“ The huge and unmeaning glass chandeliers, prism-cut, gas-litten, and without shade, which dangle by night in our most fashionable drawing-rooms, may be cited as the quintessence of false taste, as so many concentrations of preposterous folly. ”

“ But for the fond desire to be something more than an artist—to teach, to preach, to tell a story—the glazier would possibly have been quite content with the mere jewellery of glass, and might have gone on for years, and for generations, using his pot-metal as it left the pot. ”

“ Artificial light, too, is a very treacherous medium in which to examine glass of any kind. Any find should be examined by daylight and side by side with other pieces of whose authenticity there is no doubt. ”

“ In diffused lighting, the lamp is covered, as by frosting, so that the rays of light are broken up and so scattered that no direct ray shines into the eyes, and there is no bright spot of light in the room. ”

“ It is evident also that if the eye be placed just above the wick of the lamp, it will see through any particular piece of glass that very portion of the landscape which will be illuminated by a ray starting from the same spot; or the photographic image formed in the place of the flame by any one of the lenses will tell us the direction in which that lens will throw the luminous rays. ”

“ Consequently some stray beams of the light which is scattered from the oil, reach the eye, while all of the light reflected from the highly-polished glass or steel passes in another direction and is unseen. The result is a brilliantly luminous impression on a dark background. The impression ceases to be visible when the glass or steel is not well polished, and itself scatters the light, like the oil. ”