The addition of about per cent. of castor oil to the emulsion has the effect of making it less brittle and liable to crack when the paper is bent.
A very small quantity of sugar dissolved in alcohol and added will cause the collodion to adhere more firmly to the paper when it is coated on it, and so prevent it from peeling off.
The best kind of bottles for stowing and keeping the sensitive collodion are those long, sloping, yellow bottles, used to contain hock and other Rhine wines. The color of the glass is non-actinic in case any light should get to the dark-room, and further, the long sloping necks are particularly suitable in avoiding the formation of bubbles when the emulsion is poured out on to the paper.
Coating and Drying the most convenient method of coating the collodion paper is to work it in the same manner as a glass plate. If only small pieces are required, take a piece of paper, say, i x x 13 inches, and lay it on to a 12 x io sheet of glass, so that it will just overlap the glass half an inch all round. In this way it is kept flat, and an experienced collodion worker could coat it without difficulty whatever. An amateur, however, would no doubt come quickly to grief, so that an easier method must be considered.
Sheets of baryte paper are usually about 20 x 24 inches in size. Make a double frame, hinged similar to that shown in Fig. i31. This is so arranged that when the sheet of paper is laid in between and the frames closed like a book, the paper is held fast and taut. The wood-work all round prevents the collodion from running over.
Hold the bottle containing the emulsion in the right hand and the board, with the paper laid on, in the left hand.
Carefully wipe round the neck and sides of the bottle, and seee that there are no air-bubbles on the emulsion, then pour the collodion on to the right-hand upper edge of the paper.
A little practice will soon enable you to judge the right quantity, but never be too sparing. With a gentle movement incline the board in such a manner that the emulsion flows well into the top left-hand corner, then down toward the bottom left-hand edge, and finally to the right-hand corner, where the superfluous collodion is allowed to run off. But
have a care ; not into the same bottle on any account if you are going to prepare another sheet, but into a separate wide necked bottle. The bottle used to contain the emulsion for pouring on to the paper should not contain more than six or eight ounces, and should never be filled up higher than a couple of inches below the neck. The best bottles for this purpose I have found to be the wine bottles already referred to. They are usually of a non-actinic color, which is in itself an advantage. But the long gradual sloping neck prevents the formation of air bubbles. These latter will be found the chief enemy of the collodion worker, but with care and attention they can easily be got rid of. They are usually formed by pouring the collodion on to the paper at too great a height, or by bringing the bottle to an upright position with a jerk. All these little details, trifling as they may seem, are of great importance when good results are desired. The collodion must never be allowed to flow twice over the same spot during the one coating, or an unpleasant ridge visible in the finished print will be the inevitable result.
Carefully wipe the neck of the bottle each time, to prevent little pieces of the dried collodion from spoiling the film.
For the production of high-class prints it will be advisable to coat the paper twice. This is done when the first coating is thoroughly set. Turn the paper round the other way, so that the bottom and the top are reversed, and give another coating.
The superfluous collodion poured off into the wide-mouthed bottles is allowed to stand until the air-bubbles have entirely disappeared, when it can be used.
Owing to the speedy evaporation of the ether the collodion will soon become too thick. It should be thinned with a mixture of one part alcohol (.805) and two parts ether (.730). Well shake and allow to stand.
In pouring off the superfluous collodion from the paper gradually sway the board from right to left, in order to prevent the formation of ridges caused by the running of the collodion in one direction.