Drying Marks Eau deJavelle
in the bend of the joint insert a small gas burner, so as to cause a draught of air when lit. Anhydrous chloride of calcium may also be placed upon the bottom of the box. The interior may be fitted with stout wire, or glass shelves, about three inches apart. (See sketch and description under heading Emulsion.)
Drying Marks. These are generally irregular wavy marks seen near the margins of dry plates or sometimes as fairly regular patches which are of different density to other portions of the negative, and are caused by unequal drying of the coated plates, those portions remaining moist longest being more sensitive and therefore appearing as over-exposed. Drying marks are also caused in an otherwise perfect negative if the same be allowed to dry unequally or at different temperatures. For instance, if a number of plates are placed in a drying-rack close together and left for some time the centres will not dry so quickly as the edges, and unequal density may be caused; or if part of the negative be allowed to dry spontaneously and the other part be dried by the heat of the fire, or by the aid of spirit.
Dusting-on Process. See Powder Process.
Dyeing, Photographic Prints by. There are several methods of making photographic prints on textiles by true mordant dyeing. For example, calico or linen may be sensitised by moistening with a i to 10 solution of ammonium bichromate. When dry, expose under a negative and wash. The image now consists of mixed oxides of chromium, and if the textile is boiled for ten minutes or so with 5 grs. of alizarine in a quart of water, the dye will deposit on the oxide of chromium. The impression should be cleared by boiling in soap and water. (See The Amateur Photographer, Dec. 26th, 1901 ; Trenchant's book mentioned in our article, Silk, Printing on ; also, see Diazotype.)
Ean de Javelle is used for eliminating the last traces of hypo from the film, and also for reducing over-dense negatives, its action being due to hypochlorous acid. It is a solution containing an alkaline hypochlorite, and can be made as follows : -
Chloride of lime ... ... ... ... 2 ozs.
Carbonate of potash ... ... ... 4 ,,
Water ............... 40 ,,