Transparent material

“ For, if we consider first, the very faint light wherewith the object is enlightened, whence many particles appear opacous, which when more enlightned, appear very transparent, so that I was fain to determine its transparency by one glass, and its texture by another. ”

“ A transparent body, is one through which the visual line is uninterruptedly continuous from an object to the sense. The materials for glass-making are opaque, and the natural opacity of their elementary atoms is unalterable. Hence in some novel arrangement of the atoms towards promoting the direct continuity of the medium of space through them, consists the object of vitrifying and principle of transparency. ”

“ For example, the transparency of gold-leaf, which permits a bluish-green light to pass through it, is a frontier instance between transparent and opaque bodies, by exhibiting a body of the glass generally regarded the most opaque in nature, as still possessed of some slight degree of transparency. ”

“ Transparency and colour are obviously fundamentally important properties of glass. In one sense homogeneity is essential to transparency, but the aspect of the subject which we are now considering is that of the absorption of light in the course of regular transmission through glass. It may be said at once that no glass is either perfectly transparent or, what comes to nearly the same thing, perfectly free from colour. ”

“ Transparency belongs only to those bodies which have in themselves a twofold character. It will be shown that the metals are absolutely identical matters, and therefore non-transparent. The metals are the only non-transparent bodies. Metaleity = non-transparency.
350. The light falls upon a non-transparent only through a transparent body, and thus one in which the tension of light propagates itself. ”

“ In Water colours, the greater number of pigments used are transparent, and the legitimate method of using them proceeds upon the principle of working entirely in transparent media; which has, at all times, excited great hopes with regard to that branch of Art, as affording a better means than Oil colours (in which the light tints are all composed with opaque white) of producing the brilliancy and truth of Nature, in combination with the transparency (tone) which is required in a work of Art. ”

“ We are therefore obliged to suppose that the medium through which light is propagated is something distinct from the transparent medium known to us, though it interpenetrates all transparent bodies and probably opaque bodies too. ”

“ The function of the negative is, it will be remembered, to protect certain portions of the film from light, and to freely admit light where the image is, hence the denser portions of the negative must be very nearly, if not absolutely, opaque, and the image as nearly transparent as possible; thus giving what photography proper has taught us to abhor—a black and white print. ”

“ The basis for the preparation of a photo-litho is as a rule a photographic negative on glass or gelatine, which, as the word negative implies, when examined by transmitted light, must have all its tones reversed, that is to say, the drawing or the lines, strokes or points which must in the print be black, must look transparent, whilst the other part of the negative which forms the groundwork must be covered or opaque. ”

“ In the reproduction of deep black surfaces finally no rays of light are reflected, therefore no rays of light can penetrate through the screen, and because actually here no chemical change of the light sensitive film takes place, we obtain a negative which is clear and transparent in these places, that is to say without any interruption, which gives in the print a full black tone. ”

“ For all finer work and higher powers, and most generally with the low powers also, it is necessary to render the object transparent, and to examine it by light transmitted from the mirror below the stage. ”

“ When the sky and shadows are completed the main values of the picture are established, and the highlights being thin and transparent do not change the other values.
Most of the color is mixed on the paper as the work progresses and not on the palette, thus a pleasing transparent change and variety of color is obtained which can be seen by a study of the shadows and highlights in the plates. ”

“ We say that glass is transparent, because light passes freely through it, and brings the image of that which it would represent. We see an individual or tree coming freely through the glass into the room. Now if we have a medium which will pass as freely through a board, then that board is as transparent to that medium as glass is to light. ”

“ Transparencies can be made same size of negative by contact and exposure to artificial light, or enlarged or reduced in the camera by daylight, with equal perfection in result. To make transparencies by contact place one of the Keystone thin crystal glass transparency plates over the negative in printing-frame, lay piece of dark soft material over it, close down the back, and expose to the light of the lantern or to a gas flame or other artificial light, for 10 to 30 seconds, according to density of negative, at a distance of 20 inches from the flame. ”

“ Transparency becomes universal, and they are all elastic. They now form but one set of substances, and the varieties of density, hardness, opacity, color, elasticity and form, which render the number of solids and fluids almost infinite, are now supplied by a few slight variations in weight, and some unimportant shades of color. ”

“ These phenomena will be readily understood when we recollect that colour in a transparent medium arises from the fact that the medium has different absorbing powers for light of different colours. All transparent substances, and certainly glass, are only partially transparent: all light waves passing through such a substance are gradually180 absorbed, and the extent to which they are absorbed differs according to the length of these waves. ”

“ In which Experiment, there are three Observables that seem very manifestly to prove the porousness of these seemingly close bodies: the first is their acquiring a transparency, and losing their whiteness after steeping in water, which will seem the more strongly to argue it, if what I have already said about the making transparent, or clarifying of some bodies, as the white powder of beaten Glass, and the froth of some glutinous transparent liquor be well consider’d ”

“ An extremely thin film of a transparent matter, such as a little naphtha or varnish dropped on the surface of warm water or soap bubbles, or a very thin film of glass obtained by blowing out a bulb of red-hot glass till it bursts, or an exquisitely thin plate of talc or mica, all present the phenomena of colour, although they are individually transparent, and in ordinary thicknesses quite colourless. ”

“ For perfectly transparent illumination, it is much better to diffuse the light by placing under the object various substances, such as tissue-paper, ground glass, very thin porcelain, or a film of yellow bees’ wax, run between two pieces of thin glass. ”

“ Thin films are semi-transparent and have the colour of strong tea, which grows darker with increased thickness and opacity. All this is due to invisibly minute particles of black carbon suspended in a resinous medium. ”

“ The commonest form of print is on paper, although the most satisfactory print from the photographic standpoint is the transparency on glass or celluloid film.
Transparencies.—Transparencies are made by the regular photographic processes of exposure and development, on glass plates or films placed in contact with the negative, or in the appropriate position in an enlarging camera. The sensitometry and the terms used to describe the qualities of plate or film for this purpose are those already given in connection with the general discussion of plates and films. ”

“ Upon these principles Newton explains the origin of transparency, opacity, and colour.
Transparency he considers as arising from the particles and their intervals or pores being too small to cause reflection at their common surfaces,19 so that all the light which enters transparent bodies passes through them without any portion of it being turned from its path by reflection. If we could obtain, for example, a film of mica whose thickness does not exceed two-thirds of the millionth part of an inch, all the light which fell upon it would pass through it, and none would be reflected. ”

“ It will be evident from the nature of the process, that the lights and shadows of an object are reversed. That which is originally opaque will intercept the light, and consequently those parts of the photogenic paper will be least influenced by light, while any part of the object which is transparent, by admitting the light through it, will suffer the effect to be greater or less in exact proportion to its degree of transparency. The object wholly intercepting the light will show a white impression ”

“ The great importance of transparent pigments is to unite with solid or opaque colours of their own hues, giving tone and atmosphere generally, together with beauty and life; to convert primary into secondary, and secondary into tertiary colours, with brilliancy; to deepen and enrich dark colours and shadows, and to impart force and tone to black itself. ”

“ There can be no doubt that, in most of its practical applications, transparency is the fundamental and essential property which leads to the employment of glass in the place of either stronger or cheaper materials. By transparency, in this sense, we wish to include mere translucence also, since very frequently it is as necessary to avoid undisturbed visibility as it is to secure the admission of light. ”

“ The material which it uses for its content and for the sensuous expression of that content is visibility as such, in so far as it is individualized, viz., specified as color. To be sure, the media employed in architecture and sculpture are also visible and colored, but they are not, as in painting, visibility as such, not the simple light which contrasts itself with darkness and in combination with it becomes color. ”

“ The time of exposure and the strength of the developers are the most important factors in determining the quality and tone of the resulting transparency. Giving a short exposure and using a strong developer will ensure a vigorous picture with a rich velvety black tone. A long exposure, necessitating a weak developer, will produce fine gradation of light and shade, clear shadows and a warm brown tone. ”

“ The air has here, above all in the south, a transparency—oh, an infinite transparency! The despair of painters. Then this transparency gives greater purity to the outlines; nowhere do points stand out as they do here. ”

“ With regard to the strength of the solutions, it is a remarkable fact, that, if saturated solutions be employed, a negative picture is first produced, but if the solutions be three or four times their bulk of water, the first action of the sun's rays darkens the picture, and then a very bleaching effect follows, giving an exceedingly faint positive picture, which is brought out with great delicacy by the silver solution. ”

“ The transparency should be made by contact, when the original negative is of larger size than the block required; the enlarged transparency is used if the negative be smaller or the same size as the block.
The development of the transparencies on gelatine dry-plates will be treated of later, but if wet collodion be used, the manipulations will be the same as for negatives, except that the image is in reverse gradations, the lights being clear glass, and the shades dense and black. Every detail in lights, shadows, and half-tones must show distinct and strong. ”

“ In making reproduced negatives from hard originals, ordinary transparency tissue will serve every purpose. The transparency is printed in the usual way, and developed on a prepared glass plate; when dry a negative is printed from the transparency without special treatment and also developed on glass, when a decided reduction of density will be found to have taken place. The reproduced negative will possess all the good qualities of the original, plus improved printing quality. It is only in the case of extremely hard negatives that the extra special tissue is required. ”

“ Every most insignificant spot of light and shade and color, as well as the most significant, must keep its place, must hold its true relation to every other spot and to all the rest. Each value must keep its place according to the laws of fact, or it is out of touch with the whole. The whole picture must be either on a scheme of general fact, or a scheme of general arbitrary arrangement. ”

“ If a person gifted with the visualizing power in perfection should pose his eye in the place of the object-glass of the camera, would the generic image in his brain be identical with the photographic composite? (I am assuming, for argument's sake, that the photograph gives a true rendering of any optical image, which, in strictness, it does not.) ”

“ The author believes that manufacturers of artists’ material should be compelled by law to label every tube of paint as to its permanence and chemical composition so that artists could be assured that they were getting what the label indicated. ”

“ The art of producing images on prepared surfaces by means of the actinic or chemical rays of the sun’s light. The principal photographic processes now in use are the positive-, negative-, and dry-collodion processes, in each of which a thin film or skin of iodised collodion forms the sensitive surface, a plate of glass being generally used as the foundation of the film. In a positive picture the ‘lights’ are silvery white by reflected light, and the ‘shades’ are produced by a ‘backing’ of black varnish or velvet, showing through the glass plate. ”