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Handling of Sensitive Materials Loading and Unloading of Dark Slides Repacking 280

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HANDLING OF SENSITIVE MATERIALS LOADING AND UNLOADING OF DARK SLIDES ; REPACKING 280. Storage of Sensitive Materials. Sensitive materials should be stored in a dry place of moderate temperature, where they cannot be reached by any gases and emanations from volatile products. They should especially be protected from hydrogen sulphide (cesspools, or any work where sulphides are in use) and the impurities from acetylene. As we have already emphasized, the dark-room and the places reserved for the preparation of the baths and the storage of stock chemicals are not at all suitable for the storage of sensitive plates, films, and papers.

In an establishment of any size, the boxes should be stored on their sides in cupboards, or on the racks allocated for this purpose, so as to avoid any possible damage to the packings, caused by the boxes being piled one upon the other. The different types of materials should be classified according to the emulsion number.

Moisture, which rapidly passes through the ordinary packing materials, lowers the sensi tivity quite appreciably and, if the humidity is high, may cause the surfaces in contact to adhere. Heat and the majority of chemical products cause fog, which is always greater with the more rapid emulsions.

Even under perfect conditions sensitive materials undergo a more or less rapid change, which is usually more marked with films. The edges become fogged, and, as ageing proceeds, the fog band becomes broader. 2 At the same time, development takes longer, and it is no longer possible to obtain the same contrast from the emulsion as when fresh. The colour sensitivity is also affected, the red-sensitivity being lowered much more rapidly than the blue.

281. In tropical countries, the warm and very humid atmosphere tends to produce a rapid. change in the emulsions. Roll film spools ex ported to these regions are usually wrapped. singly in lead foil and packed in air-tight car tridges. Since it would be difficult to give this individual protection to flat sensitive materials, these are often placed in wooden boxes, lined on the inside with zinc foil, and securely soldered ; in this case the protection ceases immediately the box is opened. 1 Paper, which has been

rendered impermeable (e.g. by paraffin wax) may be used as a separate outside wrapper for each box, and well-made metal boxes sealed with adhesive tape are very serviceable both for the transport of unexposed emulsions and for the storage of opened packets and exposed plates awaiting development. A very efficient method of preservation is by means of a strong air-tight wooden box (interior and lid lined with a thickness of zinc), the lid of which is firmly held down by bolts or clasps on to a thick layer of indiarubber. The inside is filled. with old newspapers thoroughly dried in the sun. Well-dried newspapers form an excellent drying agent, but they must be re-dried every time the box is opened. 2 282. Handling of Materials. The order of use of the materials in each different class should be decided by the age of the material ; in this manner ageing of plates and films in stock is avoided.

The boxes should be opened neatly and put aside together with the black paper wrappings for future use in the packing and classifying of the finished negatives or for re-packing the exposed but undeveloped plates and film. The instructions should also be kept for future reference, in case it should be necessary to look up any special directions for that particular type of emulsion.

Opened packets should only be stored in the dark-room if they are to be used without delay; if not, they should be placed in stock, having first secured the packet with gummed paper, or at least with a strong rubber band. It is well to seal up the box with a label indicating the number of unexposed plates or films and the date on which the box was opened.

In an opened packet do not allow the face of a plate, film, or piece of sensitive paper to come into contact with the wrapping paper. Although certain specially-prepared or treated papers, such as those used inside roll films, film packs, and for the individual packing of X-ray plates and films, are without effect on the emulsion, it is often found that after prolonged contact with an ordinary paper, such as that used round plates and films, the structure of the paper appears on the image after development.

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