Apparatus For Reversing The Negative. The increasing employment of late of reversed negatives (for the carbon, artotype, asphaltum, and other processes) induced us to construct an apparatus with which not the object itself, hut its reflected image, is photographed directly as reversed. The apparatus consists of a rectangular prismatic box of mahogany, on the plane of the hypothenuse of which a mirror or prism is placed in such a way as to allow of easy and exact regulation of its position from the outside through the three screws appearing in the illustration. One of the planes of the casette is closed with a rough board, to protect the mirror or prism. In order to fasten the apparatus to the camera, it is unscrewed from this closing board, and screwed with the same plane on to the objective side of the camera. The other plane is closed with a movable board, which serves to hold the objective. The position of the mirror or prism is correct as soon as the image, reflected through the objective, appears in a perfectly circular form upon the dull disk, and this position is easily regulated by the screws. The apparatus is furnished with either a rectangular, complete reflecting crown-glass prism of superior finish or with a mirror. The latter consists of a perfectly plain ground-glass plate, the front side of which is well silvered, and which is of such reflecting power that only a very slight loss of light occurs, which does not occasion any disturbance even in portrait photographing. Mirror and prism reflect perfectly correct, and are of equal merit in this respect, but the loss of light is even yet slighter with the prism than with the mirror. - Romain Talbot.
The following method of obtaining reversed negatives was described by Captain O. (316)
There are many modifications sailing under various claim for originality, and patented, but it is believed that the public is entitled to what is given below, the basis of it having been published by one of the earliest workers in this direction - Prof. Husnik, in 1875. The only elaborate work upon the subject is published only in the French language by Mons.
Volkmer, as in use at the Imperial Military Geographical Institute, Vienna. The negative is wetted and coated with a warm, filtered solution of gelatin, one to thirty, poured in and drained off just like collodion, and then dried in a horizontal position. It is next coated with plain collodion, and when this is set it is soaked for half an hour in a dish of water, and then laid down flat on a table. A sheet of thick, well - sized paper having been cut to the size of the picture and well wetted is laid down on the collodion, a piece of blotting-paper is placed above it and lightly rolled down with a roller. The blotting-paper is then removed, and the edges of the collodion film having been cut to within half an inch of the paper all round are turned over the paper, and then the sheet of paper with the film attached to it it lifted off the plate. A sheet of paper is then wetted and laid down flat on a glass plate, and covered with a solution of gum-arabic, one to three. The collodion film is then laid on the gummed surface, with the paper above it; a sheet of blotting - paper is put over it and rolled down. After the removal of the blotting-paper the turned - over edges of the collodion film are laid back on the gummed paper, and the first sheet of paper is removed. Finally, a glass plate is levelled and covered with as much water as it will carry. The collodion film attached to the gummed paper is laid face downwards upon this, and the water drained off. The plate is then laid on the table again, covered with blotting-paper, and rolled. The blotting-paper is then removed, and the gummed paper stripped off. The plate is washed to remove all traces of the gum, and dried. The method is rather complicated, but seems an efficient way of performing a rather troublesome operation. - Major T. Waterhouse.
To produce reversed negatives direct in the camera use a piece of ground - glass, or a piece of plain glass covered with mat varnish in the dark-slide as a focussing - screen - the dull surface farthest from the lens. The same end may be attained by pushing the dark slides a little in just before exposure, or by turning the lens a trifle back after focussing in the usual way. Now use a gelatin plate with the glass surface nearest the lens, simply protecting the film from injury by the spring of the dark-slide. The development will, of course, be according to the directions sent out by the makers of the plate used. This method will be found to produce a result equal to, if not better than, any of the systems now in use. - Arthur F. Fenton.
Having by the following method reversed some hundreds of negatives up to twenty -four by eighteen without a single failure, it can be confidently recommended as an expedient where a reversed negative is absolutely necessary. It applies only to collodion negatives which have not been varnished. After the negative has been washed and dried, coat with a thin film of India - rubber and allow to dry. Coat over the India-rubber with plain colloidion and dry on a levelling - stand. Cut quite through the film at the edges with a sharp knife. Place in a tray of cold water, and in a few minutes the corners and edges will be seen to lift Now, by taking hold of two corners, the slightest touch will remove the tinued in order to reduce the size of the grains as much as possible. In this way two mat plates are produced at one and the same time. If a question of employing plates a second time, these, in order to from gelatin, are put into a lead or zinc vessel containing an alkali solu-tion formed of slaked lime or soda. This alkaline liquid may be preserved in good condition for more than two months, and may, by the addition of a further quantity of lime, be invigorated when necessary. In a bath of this land me hard gelatin film becomes in a period of twelve hours, end the glass may then be cleaned with sawdust, or some such material, and washed. The plates are man ground with powder in the manner just described, in order to free the pores of the glass from any gelatin remaining in them. Finally, the plates are ribbed with a rag, and rinsed in several waters, and men dried.
Leon Vidal, the distinguished photo-experimentalist and author, of Paris, from whose excellent work, Traite Pratique de Phototype, much of the information given in the notes is gathered. A workable process is thus provided for all who deem it to their advantage to test its value. This is the only photo-mechanical process it is believed that it will be necessary to treat of herein. Proceed as below.