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The photographic news
- Bandzählung
- 35.1891
- Erscheinungsdatum
- 1891
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- Englisch
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- F 135
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- Hochschule für Grafik und Buchkunst Leipzig
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- Hochschule für Grafik und Buchkunst Leipzig
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- http://digital.slub-dresden.de/id1780948042-18910000
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- oai:de:slub-dresden:db:id-1780948042-18910000
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- Bandzählung
- No. 1726, October 2, 1891
- Digitalisat
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The photographic news
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Band
Band 35.1891
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reflected through ventilating channels. Now, I can scarcely believe that there is a lantern that will stand such a test, therefore with putty, red cloths, and various devices make it as perfect as possible ; or, better than that, discard the lantern, and get a window with a well puttied-in pane of ruby glass, not larger than a half-plate, let into it, satisfying yourself that no white light can enter between chinks of the window frame ; and, as we will suppose your dark room is not perfect, work only at night, with a candle or lantern outside your window. Do not be inveigled into using yellow glass or tissue, for ruby glass of the most approved shade allows so much actinic light to pass through it that you will fog your plates to a certainty, even when working with a candle, especially if you go in for slow development, and most likely if you use a rapid developer. Since it is now so universally admitted that one thick ness of ruby glass is not sufficient to prevent the light fogging of gelatine plates, it is even more hopeless to try and work rapid films in such a light. To prove this, develop a plate that has been exposed for two minutes to the red light of your lantern or window, and you will be surprised by the amount of silver that has been deposited by such an exposure. As it seems that we cannot counteract the actinic pro perties of even red light by quality, we must perforce try quantity; therefore your ingenuity will suggest that a screen of red cloth or paper must be fixed before your red light—a screen such that it can be rapidly raised and lowered, so that towards the end of development you can momentarily increase your light to see how things are getting on. You are working almost in darkness, but as an amateur, and a beginner, let us say, you cannot be too careful; and you will find, after a little practice, that the glimpse obtained of the developing plate by the momentary raising of your curtain is sufficient to form your judgment of the amount of development attained. Always wash off the developer before holding the plate close to the red light to judge of the density. The curtain can be raised when you want to find bottles, &c. A red light so screened will allow of your opening boxes of plates in per fect safety ; even then do this in the shadow—say of your table. Since tin lanterns are so unsafe, a simple device is to cover them with a blackened box having a red glass or tissue window, and screened ventilating apertures. Fogging also takes place during exposure; it occurs by reflected light reaching the plate, when the shutter is drawn through the slit in the lens tube used to insert the stop. As almost every lens is fitted with Waterhouse diaphragms, it is impossible to make them fit so perfectly that no light can enter; therefore, to prevent such an untoward circumstance, bind a long strip of black cloth round the lens tube, so that the stop aperture shall he light tight. It is extraordinary how few amateurs know of this. To prove it, raise the ground glass, stop and cap the lens, and cover your head and the camera (not the stop slit) with the black cloth, and notice, when your eyes have become accustomed to the gloom, how much light really enters through this fatal slit. An innumerable number of negatives are fogged by this and called over-exposures. Thus, how frequently one hears and reads accounts of over-exposure of half-plate landscapes with the smallest stop, having received a four-second exposure—an impossi bility as regards the picture, but true enough when applied to the amount of light that reached the plate, for fogging has been going on between the moment of drawing the shutter and the removal of the cap. I have given with half-plate R. R. lens and f IM slop (the smallest) eight seconds to brightly lit Himalayan snows without foliage, and not found it too much ; but then, though the plates were extra rapid, the negatives were produced without fog. Light-fogging also occurs when photographing to wards the sun by the direct rays shining into the lens tube, and if the slides are exposed to sunlight. The prevention required to neutralise those two causes is obvious. Having eliminated all sources of light-fogging, it is wonderful how impossible within reasonable limits it is to. over-expose; and again, with full exposure, what beautiful features a negative will possess, supposing it to be one required to show a dark foreground, distant snow-clad hills, and the delicate shading of clouds; these will appear with the requisite tone and details. After all, what is a negative that shows no light-fog ? It is one whose border is perfectly clear, and whose very deepest shadows only show clear glass. Lastly, as a beginner, fly from light-fog as you would from a loathsome disease. The experienced photographer can manipulate plates in an actinic light; but, as an amateur and a beginner, you cannot; so do not copy him till you are proficient. —Journal of the Photographic Society of India. LUMINOUS PAINTS. For orange luminous paint, 46 parts varnish are mixed with 17'5 parts prepared barium sulphate, 1 part prepared India yellow, 1’5 parts prepared madder lake, and 38 parts luminous calcium sulphide. For yellow luminous paint, 48 parts varnish are mixed with 10 parts prepared barium sulphate, 8 parts barium chromate, and 34 parts luminous calcium sulphide. For green luminous paint, 48 parts varnish are mixed with 10 parts prepared barium sulphate, 8 parts chromium oxide green, and 34 parts luminous calcium sulphide. A blue luminous paint is prepared from 42 parts varnish, 10'2 parts prepared barium sulphate, 6*4 parts ultramarine blue, 5'4 parts cobalt blue, and 46 parts luminous calcium sulphide. A violet luminous paint is made from 42 parts varnish, 10'2 parts prepared barium sulphate, 2’8 parts ultramarine violet, 9 parts cobaltous arsenate, and 36 parts luminous calcium sulphide. For grey luminous paint, 45 parts of the varnish are mixed with 6 parts prepared barium sulphate, 6 parts prepared calcium carbonate, 0'5 parts ultramarine blue, 6’5 parts grey zinc sulphide. A yellowish-brown luminous paint is obtained from 48 parts varnish, 10 parts precipitated barium sulphate, 8 parts auri- pigment, and 34 parts luminous calcium sulphide. Luminous colours for artists’ use are prepared by using pure East Indian poppy oil (in the same quantity) instead of the varnish, and taking particular pains to grind the materials as fine as possible. For luminous oil-colour paints, equal quantities of pure linseed are used in place of the varnish. The linseed oil must be cold pressed, and thickened by heat. All the above luminous paints can be used in the manufac ture of coloured papers, Su:., if the varnish is altogether omitted, and the dry mixtures are ground to a paste with water. The luminous paints can also be used as wax colours for painting on glass and similar objects, by adding, instead of the varnish, 10 per cent, more of Japanese wax, and one-fourth the quantity of the latter of olive oil. The wax colours pre pared in this way may also be used for painting upon porcelain, and are then carefully burned without access of air. Paintings of this kind can also be treated with water-glass.—American Druggist.
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