Scientific and Useful

New Zealand Graphic, Volume XL, Issue 19, 6 May 1908, Page 52

Scientific and Useful

CARBON PRINTING. It may not perhaps be known to many of the amateur workers in carbon that a certain amount of personal control can be exercised on the wet print while still in the hot water for the heavier portions, and again when in the cold wa. ter for the lighter parts. Carbon tissue is extremely tender, and great care must bo exercised in trying alteration. A very soft sable brush will be necessary, and the manipulation is best done jusb under the surface of the water. If, owing to the water being much stained by the wash-out of the print, this be difficult, the print should be very rapidly transferred to a dish of clean water of the same temperature and the work done there. Much lifting in and out will result in reticulation. When the print is ready for the cold water it should be immersed till the tissue is quite cool, and then delicate work, such as indications of breaks in the sky and strengthening of lights in water, etc., may be undertaken. Extreme caution will have to lie used all through these operations, or disaster is certain. * ♦ * FEEDING HORSES BY CLOCKWORK. A provision merchant in Oldham (England) has invented an ingenious contrivance by which, it is stated, he is able to feed his horse without personal attendance, through the medium of a 4/6 (American alarm clock! In a small office adjoining the stable the clock is placed on a shelf. Attached to the winding-up key is a piece of copper wire, and this is fastened to a Ismail brass roller that runs over a .wooden rod. At the end of the rod is a heavy weight. When the clock “goes off” the wheel is drawn over the rod and releases the weight, which falls to the floor. The corn box is filled overnight, and immediately the weight is released a email door at the bottom of the box flies open and the corn falls into the manger. IThe horses never fail to rise at the sound Of the alarm, knowing what is to follow, end when the drivers turn up, say, at 7 or 8 o’clock, the animals' are ready for taking the shafts. Another advantage to be gained by the method is that the horses need never l>e placed in the (shafts before the greakfast has had time to digest. * * DRYING NEGATIVES. The rapid drying of negatives is a problem always with the amateur; indeed, haste in all departments of work is a feature of these strenuous days. r A bath of alcohol is often recommended for removing a large proportion of that water which saturates the gelatine film, but not a few have experienced that the cult of haste by the use of alcohol too often leads to delay and occasionally to spoiled negatives, a fatal cloudiness of the film arising in many cases. True it is that this cloudiness may often be removed by soaking the negative in water for some hours, and then allowing the plate to dry quite slowly or in the ordinary way;, but sometimes the negative never recovers its original clearness, and so is inevitably spoiled. The cloudiness does not appear to depend so much on the use of impure or pure alcohol, provided that extremely strong alcohol is avoided, the sudden removal of the water from the outer surface of the film by strong alcohol appearing to leave the film in a spongy state so that the light passing through is broken or diffused; but if the alcohol is diluted with from half its volume to its own volume of water, this spongy condition does not arise. Methylated spirit, or, at any rate, that form of methylated spirit which is easily obtainable, becomes slightly milky when diluted with water, but orrlinarily no mischief follows. Curiously enough, and contrary to what might be expected, the weakened epirit removes water almost as rapidly as a stronger ■pirit, doubtless from the fact that the

surface of the film does not become hard or horny. On removal from the alcohol bath the plate or print must be thoroughly blotted off with blotting paper or a soft cloth, and if the plate is now held before a fire at just such a distance as to avoid softening, and fanned all the time with a piece of mill-board, the drying may usually be completed in six or seven minutes. Thus we have, say, eight minutes in the alcohol bath, and six minutes before the fire, or fourteen minutes in all, allowing nothing for the few seconds involved in blotting off. In drying l>efore the fire rapidity depends wholly on gradually increasing the warmth as the plate becomes dryer, or in so adjusting the heat that the gelatine just does not melt. One who carefully practises with waste negatives will soon realise that peculiar shiny appearance . of the film which is just on the point of . melting. When, however, the photographer has acquired the art of delicately adjusting the heat to the state of the film, he may save time by carrying out the whole operation in front of the fire;

but he should not forget the great gain in time which results from the use of a fan. Again, it is a great help to use a 1 in 20 formalin bath as the final wash-water, thia serving to harden the film and give it heat-resisting qualities. Atl the above remarks as to the drying of negatives apply more or less to gelatino-bromide. gaslight, and most other prints, but as the sensitive films are ordinarily thinner in the case of papers drying becomes much easier. F + ♦ LIGHTNING CRACKS PHOTOGRAPHIC PLATES. Lecturing before the Royal Photographic .Society, London, Mr. K. J. Tarrant, F.R.A.S., said one of the most curious things about the protography of lightning flashes or other electrical discharges was the frequency with which the photographic plate would fly into many pieces of most fantastic shapes on exposure. The effect, he stated, was doubtless due to intense strain on the glass. + 4- ♦ PHOTOGRAPHING CLOUDS. Many cautions are needed when clouds are to be our subject. They must be selected from a portion of the sky which will be likely to suit landscape subjects—it would! Iks manifestly unsuitable to print clouds taken well above our heads into an ordinary landscape.

Then they must have definite form and arrangement; it is useless to take simple masses of cloud which can in no way help the composition of the picture. The clouds require, from the point of view of picture-making, quite as much attention as the landscape, and they can often redeem a subject which, without them, would have to be given up as hopeless. The direction in which the landscape is lighted has to be kept in mind, and ths clouds taken that are in a similar posi« tion as regards the sun, so that the lighting scheme may hang together and be homogeneous. Various writers favour different methods of exposing for skies, some stooping down to F. 64 and giving a very rapid time exposure, and other* favouring an extremely rapid exposure with the open lens. But whichever method be employed, the subsequent negative must be kept quite thin.