The Optical Magic Lantern Journal (February 1897)

34 The Optical Magic Lantern Journal and Photographic Enlarger. quantity, instead of saying how many quart pots it would fill, and here, again, we bring the analogy nearer to the electrical standard, for it is not convenient to measure the capacity of electricity. So we may say that a stream of water of a certain thickness, flowing at a certain pressure, will do an amount of work directly proportional to the sum of these two factors. Supposing that the stream was one inch in thickness and the pressure 100 pounds on the square inch, those two factors multiplied together represent a certain amount of power to do work. If the pressure were 200 pounds, or the stream twice the thickness, twice as much work could be accomplished, or if these doubled conditions existed together, they would represent energy of four times the original amount. (To be continwed.) sit The Invention and Development of the Optical Lantern. By EDWARD DUNMORE. CHAPTER XI. LIDE painting, like painting any other picture, requires an artist to do it properly, but as we allude particularly to photographic transparencies, a knowledge of drawing is not so imperative as that of mixing colours. Tbe colours them selves are transparent oil colours in collapsible tubes; selections of them are especially made up for this purpose, and sold in sets by artists’ colourmen. Barnard, of Berners Street, W., has for many years made a speciality of these colours. Of course, any good transparent oil colour by any maker will be suitable. The most generally used colours are: Ivory black, neutral tint, burnt sienna, brown, pink, yellow lake, raw sienna, Italian pink, Chinese orange, rose madder, brown madder, purple madder, crimson lake, carmine, Indigo and Prussian blue, with a little magilp mastic varnish and light drying oil. A retouching desk is an advantage, but a piece of stout glass 10 inches by 12 inches framed, and with a couple of struts to support it at an angle, about twice as great as that of an ordinary writing desk, with a piece of white cardboard laid below it, will answer every purpose A flat wooden bar, sliding up and down on the face of the glass working in slots fixed to each side of the frame as a support to the slide being painted, is also a convenience; also a mask of opaque paper covering all the glass except an aperture for the slide being painted. Suppose we desire to colour a landscape, we Squeeze out a little of the colours that are required on to a slab from the tubes in | dabs, separated by about an inch or so, with a little magilp and varnish. The sky is first painted, using a little blue mixed to a suitable consistency with magilp; it should be rather stiff. After sparsely brushing it on, dab it with the end of the fingers until it becomes quite an even layer; a little rose madder may be introduced near the horizon, and over distant hills a little deeper blue with a little purple near the bottom. All this portion of the slide must be made even by dabbing, the drawing being already formed by the photograph itself. The next point is to introduce yellows and browns into the foreground to be followed by greens of various shades for the trees; then touches of bright local colours on objects in the foreground. The golden rule is to use as little colour as possible on any part or parts of the subject, often photographs with merely a slight tint will look far better than if they are more deeply coloured. If clouds are required, being absent on the photograph, after putting on a flat tint for the sky, take a bit of rag twisted up to a point, and wipe off some of the colour where clouds are required. Cumulus and other elaborate forms of clouds require a skilled artist to put them in satisfactorily. If such prominent clouds already exist in the picture a very slight tint may be placed on the shadows, diluting the colours used with magilp and a little oil taken up on the point of the brush. When the painting is finished, place it out of the dust to dry, Japanners gold size is often used to mix the darker colours with, or white turpentine varnish for the more delicate ones. A very quickly drying varnish is difficult to work, and any varnish that will not dry perfectly transparent without heat should be avoided. Very high lights may be removed with a needle or knife point used with extreme caution, leaving, of course, the bare gelatine. If the gelatine is cut into, the edges of the cut will often appear as defects. It rarely happens that a pure colour, as from the tube, is so suitable as one with an admixture of some other to take off its crudity and alter its tone. Fore