Many as are the processes which have been evolved by the ingenuity of the chemical experimenter, it cannot be said that we yet have a perfect process of intensification, speedy in use, performed in one operation, and thus capable of being stopped at the required stage and permanent in the results Hitherto, with one exception, all intensifies have been based upon the use of mineral or inorganic compounds, such as the metallic salts which exert an oxidizing action upon the silver deposit, and thus, in one way or another, allow of an increase of density. The exception to which we refer the single example of an organic intensifier is that invented some eight or nine years ago by MM. Lumiere, in which the oxidizing agent is a quinone compound. The departure thus made into the infinitely wide field of organic chemistry is one which has not been followed, although there is every probability that among the many compounds and series of compounds of carbon which exist there are some in which the two properties of oxidizing the silver image and of adding density when so doing are united. Now that the demands of photography, in the matter of developers, are becoming familiar to makers of organic products and intermediates in this country it may happen that the sister process of intensification may come in for a share of attention, even though the commercial rewards may be small in comparison with those yielded by a developer.
The Donalty of Negative Fog.
The old idea that a negative must have a certain amount of clear glass is held by few printers now, but it is an undoubted fact that with a negative that is at all inclined to be on the thin side a very slight amount of fog reduces the printing value in a marked degree. It also gives a false impression of the real contrast present and prevents proper judgment of exposure when bromide or other development papers are used. It is an instructive experiment to reduce with ferricyanide and hypo one half of a foggy negative until the shadows are fairly clear, when it will usually be found that although the image, plus fog, appears fairly vigorous, yet, minus fog, it is really quite weak. It is therefore evident, when a negative cloud over in development more than it should do, that the development should be prolonged until considerable density is obtained; then when the fog is removed what is practically a normal negative will be left. If any one suffers from this class of negative, it is advisable that all precautions should be taken to avoid all possible causes of veiling. A very common one is diffused light in the camera; this may be through insufficient shading of the lens, to a dusty or cloudy condition of the glasses, or even to reflection from imperfect blacking of the bellows or woodwork. It is curious fact that in the wet collodion era, when there was much lees liability to fogging, photographers was very careful as to shading the lens with long hoods, cones, or canopies, while now we may find people using rapid anastigmats with half-inch hoods or none at all, and this with ultra-rapid plates. The point should receive especial attention at the hands of those who go in for «fancy’ lighting, with the lens pointing more or less directly to the light. With dirty lenses the remedy is obvious: a little alcohol and a soft rag are all that is needed, although a coating of dead black or even black velvet inside the lens tube, is a valuable addition, while treatment with a really dead blacking such as nitrogen on the bellows and framework should complete the cure. If the fogging occurs in the camera the edges of the plate where protected by the rebate should be clear, otherwise the cause must be sought in the dark-room. Coloured fabrics fade and some red glasses permit a considerable proportion of blue light to pass through. It is worth taking a little trouble in tracing the cause of fog in order to secure clean, easily printed negatives.
Glass for the Studio.
A correspondent recently asked whether the use of rolled or ground glass for glazing the studio would obviate the necessity for white blinds or curtains in addition to dark ones. In our opinion, in an at all well-lighted position it would not do so, as although either kind would prevent the direct glare which sometimes comes through clear glass, there would, be no effective control of the light. There is, however, much to be said in favour of what is generally called "rolled plate" for both roof and sidelights. For one thing, it effectually excludes all view from the outside, even when using artificial light, while another advantage is that the light is more evenly distributed about the studio, with the result that the shadows are less intense, and the exposures shortened in spite of a certain proportion of the light being absorbed. If the glass is neglected dust and dirt will accumulate in the ribs and cause considerable waste of light, but an occasional wash with soap and water, applied with a soft brush, will remedy this. Of ground glass we cannot speak so well. It certainly diffuses the light and is, therefore, useful where there are outside obstructions, for it is well known that a side light of ground glass will give better illumination if there is a wall near than clear glass On the other hand, it rapidly gets yellow in a smoky atmosphere, and it is then more difficult to clean than the rolled plate. Moreover, as it diffuses the light more than rolled or clear glass, it is more difficult to get decided effects in lighting with it.
Defects in Sketch Portraits.
Few photographers pay sufficient attention to the lighting of the sitter when producing negatives for sketch portraiture and many examples that we have seen in professional show-cases point to negligence in this respect The charm of a good sketch portrait, in our opinion, lies in its fine tonal quality and delicacy, while if an over-harsh or too unequal lighting is arranged a very inferior effect is obtained. One of the best sketch portraits that we have seen was made with a decidedly flat lighting, but one that, at the same time, by the aid of first-class photography, was a delightful result of tonal quality and colour suggestiveness. While on the subject a word may be added with reference to the sitter’s costume. In the case of feminine sitters the sketch portrait should always be in a high key and if possible the receptionist should advise light clothing free from any trace of dark. We recently saw a bust sketch portrait of a feminine sitter in a high key that was absolutely ruined from the artistic point of view by the inclusion of a dark tie. The removal of this should have been: tactfully suggested by the photographer. Many child -portrait sketch effects in a high key are considerably reduced in artistic value through a dark-coloured hair ribbon, and: we have before us a delightful full-length sketch portrait of a youthful sitter in a light dress completely spoilt by reason of the fact that the sitter is wearing dark socks, or, perhaps, those of a colour that photographed too dark, if a non-earthy plate was employed. The above are some points that have a real bearing upon success and' should be noted by all sketch portrait workers.