From the Photographic Times.
Transparencies for the decoration of windows, or gas shades, or for examination in the stereoscope, differ from those intended for lantern projection in being somewhat more intense. A lantern transparency must have its high lights of pure glass; in the case of the others, it is of less consequence, should they be slightly shaded.
To produce a transparency by wet collodion, a camera is required the body of which will be capable of extending to twice the focus of the lens, although a still further extension is desirable. The reason for this lies in the fact that when making a transparency the same size as the negative, the sensitive plate must be withdrawn from the lens to the extent of precisely twice the solar focus. It occasionally happens that it is desirable to make the image in the transparency on a scale a little larger than that in the negative. To permit of this being done, it is necessary that the distance between the sensitive plate and the lens be increased, for according to this distance, so is the amount of enlarging.
The negative must be so arranged as to have a clear sky or a uniform light behind it. If the work is to be effected at a south window into which the sun is shining, the requisite uniformity of illumination is obtained by placing a sheet of ground glass within a few inches of the negative. Arrangements must be made by which the negative may not only be held rigidly in an upright position, but that such adjustments may also be made as will bring it as near to or as far from the lens as will be found requisite, and also as will permit of its being raised, lowered or having any part far removed from the centre brought into the axis of the lens. These conditions are fulfilled in all good transparency cameras. We do not assert that a properly constructed camera for the special purpose of making transparencies is an absolute necessity, seeing that a light framework erected in front of the camera, and with which it need not be connected with a bellows body, will suffice, but the great convenience of a camera expressly for the purpose cannot be overrated.
In order to ensure clearness of the high lights, the collodion should be rendered of a dark sherry color by the addition of a few drops of an alcoholic solution of iodine. The strength of the solution is not of consequence, but enough must be added to the collodion to render it of the color indicated. Collodion for this purpose works rather better after it has been kept for a few weeks or months than when it is quite new. No hints can here be given as to the length of exposure requisite, but if the camera be pointed to a moderately bright sky, the negative one of average density, and the lens worked with a small diaphragm, an exposure of twenty-five or thirty seconds may be given, and, by noting carefully the quality of the resulting picture when finished, the data for a more accurate timing of the exposure may be ascertained therefrom.
After developing the image with iron, if it should, upon examination prove to be too thin, wash off the developer and apply pyrogallic acid and silver and bring it up to the required intensity. Fix and wash.
At this stage - that is, after fixing and previous to the plate being dried - the image may be toned to almost any desired color. It is to be regretted that some of the most desirable tones cannot be recommended, on account of the want of permanence. A type of the best of this class of toning agents is as follows: Make a saturated solution of bi-chloride of mercury in hydrochloric acid and dilute it with twelve volumes of water. Into this place the plate, after having thoroughly removed the hyposulphite by washing. When it has become quite bleached, wash carefully again and place in a bath composed of a dram of sulphide of ammonium to a pint of water.
The image will soon acquire a rich dark brown color, and when this is found to have penetrated the film, it may be washed, dried and varnished.
A solution of sulphide of potassium imparts a good brown color.
Chloride of gold gives a tone which may be described as a neutral black, that is both durable and very pleasing for quite a variety of subjects.
A solution of chloride of platinum gives a tone which is very permanent. It is essential when using either gold or platinum that the toning solution be weak.
It is possible, however, so to develop a collodion transparency as to obtain a rich purple black tone without any after toning. The addition of a few drops of a saturated solution of citric acid per ounce of developer effects this, but as it checks development at the same time, the proportion of protosulphate of iron must be increased to such an extent as to impart energy to the developer
A few drops of a solution of gelatine in sulphuric acid is also of great utility when added to an iron developer. It promotes clearness of image and richness of tone.
Anthony's Bicycle Camera.
How delightful a pleasure it is in the early morning, or of a fine afternoon, to mount a bicycle and take a spin along the country roads.
The bracing air, the easy motion, the sense of independence, so act upon the mind as to make it keenly sensitive to the beauties of the foliage and scenery that so swiftly pass before the eyes. Such must have been the thought of him who penned the following: