Distilled water...... 1 ounce.
Dissolve and filter.
The quantity of this fluid necessary to be made must depend upon the form of trough to be used, whether horizontal or vertical, and also upon the size of plate. The kind used by Mr. Home is the vertical, though many still prefer the former, and attach a piece of Indian rubber to the back of the plate as a handle whilst applying the collodion, and to keep the fingers from the solution whilst dipping in the bath. With the vertical troughs a glass dipper is provided, upon which the plate rests, preventing the necessity of any handle or the fingers going into the liquid. If, however, the glass used is a little larger than is required, this is not necessary. Having then obtained one or other of these two, and filtered the liquid, previously free from any particles of dust, etc., the plate is to be immersed steadily and without hesitation, for if a pause should be made at any part, a line is sure to be formed, which will print in a subsequent part of the process.
The plate being immersed in the solution, must be kept there a sufficient time for the liquid to act freely upon the surface, particularly if a negative picture is to be obtained. As a general rule, it will take about two minutes, but this will vary with the temperature of the air at the time of operating, and the condition of the collodion. In cold weather, or indeed anything below 50° Fahrenheit, the bath should be placed in a warm situation, or a proper decomposition is not obtained under a very long time. Above 60° the plate will be certain to have obtained its maximum of sensibility by two minutes' immersion, but below this temperature it is better to give it a little extra time.
To facilitate the action, let the temperature be what it may, the plate must be lifted out of the liquid two or three times, which also assists in getting rid of the ether from the surface, for without this is thoroughly done a uniform coating cannot be obtained; but on no account should it be removed until the plate has been immersed about half a minute, as marks are apt to be produced if removed sooner.
Having obtained the desired coating, the plate is then extremely sensitive, and, therefore, we presume the operator has taken every precaution to exclude ordinary day-light.
The room must be closed against any portion of day-light, and candle alone employed, placed at a distance from the operator to give the requisite light. Yellow glass, which has been recommended for glazing the operating room, does not furnish sufficient protection from the chemically active rays.
The plate thus rendered sensitive must then be lifted from the solution and held over the trough, that as much liquid as possible may drain off previous to its being placed in the frame of the camera, and the more effectually this is done the better; at the same time it must not be allowed to dry.
The question is often asked, how soon after coating the plate with iodized collodion should it be immersed in the nitrate bath? Now, this is a difficult question to answer. We have said the time of immersion is dependent upon the temperature and quality of the collodion; so likewise must we be governed as to time before immersion. To make collodio-iodide or xylo-iodide, for, chemically speaking, there is no difference in the two, it is necessary that the ether should contain a certain quantity of alcohol, or the different articles are not soluble: therefore, if we take a fresh bottle, and coat the plate from this, it contains its full dose of ether, and with the thermometer ranging between 60° and 70° the evaporation will be very rapid, and consequently a tough film soon formed. If, on the other hand, we are using a solution which has been in use some time, and many plates, perhaps, coated, the proportion of alcohol is much greater, and not being of so volatile a nature, it will necessarily take a longer time to acquire the requisite firmness for immersion. If, for instance, after coating a plate, we find on immersion it does not colour freely, we have then reason to suppose the plate has not been immersed sufficiently quick; but if, on the other hand, we find the film very tender, and upon drying it cracks, then we have reason to know that plates prepared from that bottle must not be immersed quite so soon. The larger the proportion of alcohol the more sensitive will be the plates, and the quicker and more even will be the action of the bath; but a longer period may be allowed for the sensitive film to harden before immersion.
The next question also often asked is, how long must be the exposure in camera? a question more difficult to answer than the last, without knowing something of the character of the lens and the intensity of sunshine. Practice alone can determine, combined with close observation of those parts which should be the shadows of a picture. If, for instance, in developing we find those parts less exposed to the light than others developing immediately the solution is applied, then we have reason to suppose the exposure has been too long ; but if, on the contrary, they develope very slowly, we have proof the time allowed has not been sufficient to produce the necessary action. In a good picture we should see first the whites of a dress appear, then the forehead, after which we shall find, if the light has been pretty equally diffused, the whole of the face, and then the dress.
The following remarks, by the Count de Montizon, are of value—
I have tried many methods of iodizing collodion. Those which have given the most successful results are the following:—
In 1 oz. of collodion put a little iodide of silver and about 3 or 4 grains of iodide of potassium, and then shake it well up. The collodion becomes very turbid, but on being left for some hours it gradually clears up, beginning at the bottom. When it is quite clear, pour off the liquid into another bottle.