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The photographic news
- Bandzählung
- 27.1883
- Erscheinungsdatum
- 1883
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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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- Bandzählung
- No. 1277, February 23, 1883
- Digitalisat
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Zeitschrift
The photographic news
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Band
Band 27.1883
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- Titelblatt Titelblatt I
- Register Index III
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Band
Band 27.1883
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- Titel
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124 THE PHOTOGRAPHIC NEWS. LFEBRUARY 23, 1883. 1 .—Finest gum arabic 2} parts Water ... ... ... 35 ,, 2 .—Bichromate of potash 1 ,, Water 30 „ Albumenized paper may also be used by itself for photo lithographic transfers. The sensitizing bath should be a solution of bichromate of potash containing alcohol, and the paper must be floated on it albumenized side upwards, so as to avoid dissolving off the albumen. With albumenized paper it is rather difficult to keep the ground free from ink in the white parts. {To be continued.) ON THE MOUNTING OF PHOTOGRAPHS, AND INJURIES CAUSED THEREBY.* It is a well-known fact that the fading of photographs is caused not so frequently by the actual mount, as by the mounting material employed. Sour paste or gum has spoilt many a fine picture, the green mould decomposing the albumen upon the surface of the print bringing about the oxidation of the silver. It appears almost unnecessary to waste time talking of this well-known circumstance, for everyone using these substances kuows what is to be feared, and recognises directly the cause of fading. The conditions under which paste begins to decompose by the formation of microscopic organisms are at present by no means so fully known as to enable it to be stated with certainty in every single case whether decomposition has really set in or not. The germs existing in starch may easily be destroyed by boiling, but after a few hours’ exposure to the air they are found again in great numbers, without reckoning those which in certain cases adhere to the card or back of print. The speed with which these germs multiply varies according to the situation of the room in which the mounting goes on, and that of the storage rooms for cards and pictures. Even when present in large numbers, they only exert a pernicious influence when the paste has been sufficiently exposed to convert the germs into fungi. Insummer two hours sometimes suffices ; in winter it takes as many days. Where there are not many pictures to be mounted, and they can all be allowed to dry before putting away, the danger of mildewing is not great, provided fresh paste be used. On the contrary, when many have to be done at the same time and packed up when only half dry, or with large pictures to avoid damaging them, they are placed between sheets of card in a drawer to the exclusion of the air, such conditions would conduce to the development of organic germs. Of course many circumstances have to be con sidered which do not appear at first sight, and therefore the real cause of the mischief does not always come to light. For instance, mounting boards should be examined both as to their storage and the manner in which they are arranged, so as to discover if some be relatively free from mould germs, and others attract them, whether the boards are kept from the damp, or the mounting paste itself be at fault. The photographer looks for a reason in the appearance of the cardboard itself, and excludes the pre sence of injurious substances such as hyposulphite, chlorine, &c. If when under examination by a chemist a negative result is given, he thinks there must be some mistake, while the real cause would be more easily observed through a microscope than by all the reagents of a laboratory. Is the photographer really quite helpless in this matter? It would seem so. The room for the mounting, packing, and pressing of pictures cannot be changed ; it is most likely difficult to ventilate, and therefore highly favourable to the development of mildew. Space may be very limited, and cause the greater need for stacking up even small • Photographitches Wochenhlatt. photographs. What is to be done, then, to avoid this apparently unavoidable evil ? The remedy is simple and certain, while at the same time it possesses the advantage of not absolutely requiring that fresh paste should be made every time. It consists in the addition of some chemically pure carbolic acid directly after the paste is made. The antiseptic properties of this substance are well known. The germs already existing will be destroyed by it, and their formation effectually prevented where the pictures are still damp. The paste keeps so well that it may be used for weeks after its preparation, while usually it cannot be used after a few hours in hot weather. I cannot recommend this addition too highly to photographers, as it removes at once one of the greatest dangers from their pictures. Now comes the question of how much should be used. I give the following as an excellent mounting paste. This subject should not be treated too lightly; it is so important to the whole appearance and duration of photographs. Some good wheatflour, not potato or rice starch, is mixed with a little luke-warm water in a warm jar to the consistency of thick batter, to which boiling water is added while stirring. It is important that the right quantity of luke-warm water should be used in the first instance, as, if too thick, it becomes lumpy ; if too much water, it is thin. Only so much boiling water must be added to make the paste when hot as firm as very stiff batter. An equal amount of a ten per cent, solution of gelatine, and one- third of spirits of wine, in which six grammes per litre of carbolic acid have been dissolved, are added to the paste. This mounting material lasts good for a long time, and must be used just warm, as when cold it assumes the con sistency of gelatine. This paste, although somewhat expensive, is exceedingly convenient to use. Dry albumenized photographs, when spread with it, do not roll up so much, and this is of great advantage for large pictures, as they stretch when made wet, and cause the card to cockle. Wetting the card to avoid this is of no use, as the albumenized surface con tracts so much on drying. If a photographer finds, sooner or later, tiny light spots covering his pictures, often arranged as showing the sweep of the paste-brush, let him try the addition of carbolic acid, and in most cases the evil will be remedied. In most cases, but not always. There may be other reasons besides formation of mildew, and the chief one may be put down to the use of the so-called bronze card mounts. This favourite mode of decoration is obtained by sprinkling bronze powder over the card. If such mounts contain ingredients likely to affect photographs, this affords a ready means of causing them to fade. By analysing the composition of different bronze tints, gold being debarred from general use on account of its cost, the following results will be found on referring to Koenig. Copper. Zinc. Tin. Light yellow 82-3 16-7 — Bright yellow 84-5 15-3 — Reddish yellow 900 9-6 — Orange 99-0 0-7 — Copper red 99-9 ------- — Violet 98-2 0.5 ----- Green 84-3 15-0 —. White — 2-4 96-5 The ingredients in the various bronzes are heated and mixed with grease as protection from the carbonic acid in the air. Without further discussion, it may be seen that these bronzes cannot exert sufficient influence upon photographs to affect them, and upon the whole are indifferent to silver pictures. On this account I have never heard of pictures fading when mounted on cards printed with these so-called gold-bronzes. But for very cheap mounts for which the large amount of copper required by the table above is too expensive, bi-sulphide of tin (aurum musivum)
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