A Manual of the Collodion Photographic Process - Iodize the Collodion
Contents
Part 1
Part 2
- Preparation of Collodion Film
- Immersion of Plate in the Bath
- Exposure of the Prepared Plate to the Action of Light
- Development of the Image
- Fixing of the Image
PART III
- The Whitening Process
- The Camera
- Description of the Camera
- Glass Bath
- Photographic Lens
- Summary of Precautions
- Conclusion
To Iodize the Collodion
The next step is to iodize the collodion. In the first place, a solution of iodide of silver, dissolved in an alcoholic solution of iodide of potassium, must be prepared.
The mode I gave in my first account of the collodion process, in the March number of the “Chemist” for 1851, is the most ready way of obtaining this solution.
Prepare a saturated solution of iodide of potassium in alcohol, say 1 oz., and add to it as much iodide of silver as it will take up. Or to 1 oz. of alcohol add an excess both of iodide of potassium and iodide of silver; after a day or two, and with repeated shaking at intervals to facilitate the operation, a saturated solution of the two salts will be obtained, and if this is filtered off into another bottle it will always be found ready for use. The first bottle can be kept as a stock bottle, to obtain a still further Supply by replenishing it with alcohol, and adding now and then small additional quantities of the two salts.
The iodide of silver can be readily obtained by precipitation. For instance, take 1 oz. of solution of nitrate of silver used in the process, 30 grs. of nitrate of silver to 1 oz. « of water, and add to it sufficient of a solution of iodine of potassium in water as will throw down the whole of the nitrate of sijver as an iodide. When this precipitated iodine of silver has settled, which it very readily does, the liquid above must be poured off, and fresh water added, repeating this washing several times.
The iodide of silver after this is nearly dried, and then put into a bottle with a small quantity of alcohol just sufficient to keep it moistened. The quantity of this solution of iodide of silver which can be added to 1 oz. of collodion must depend upon the quantity of alcohol in the collodion, as I have previously remarked ; so that exact proportions cannot be given; but with ordinary care and a little caution there will be found no difficulty on this point; and if, after having put, say, 5 drops of the solution to 1 oz. of collodion, it is found weak in colour, more must be added until the requisite density is obtained, which can be judged of by pouring a little on to a slip of glass and dipping it into the nitrate of silver bath.
The collodion cannot be used directly after — iodizing: the drawing made with it would — be full of spots: it requires at least a day to settle; and great care must be taken afterwards not to disturb any sediment there may happen to be at the bottom of the bottle. The solution should be kept in a cool place, especially — In summer.
Having now given directions for the preparation of the iodized collodion, I will proceed to describe the manner in which it can be used to most advantage.
Since I first published the process various modifications in the manipulations, and strength of the solutions, have been suggested; as, however, they do not differ materially from the original mode, there will be little gained by giving them in detail.
A small quantity of bromide or fluoride of potassium, or of arsenious acid, may be added to the solution. However, they do not accelerate to any great degree.
A stronger solution of nitrate of silver may be used at times with advantage, as it would tend to increase the sensibility of the preparation, but it would be liable nevertheless to dissolve out the iodide of silver from the film, when immersed in it, unless a small quantity of iodide of silver be previously dissolved in it.
This peculiarity will be best shown by the following experiment: Prepare a strip of glass with collodion ; iodize it in the nitrate of silver bath, and afterwards allow it to dry, placing it at a small angle against any support. Presently, from the evaporation of the silver solution on the surface of the film, the iodide of silver will be gradually dissolved out, leaving the collodion film colourless and transparent. It will thus be seen, that although the weak s0lution has not this power, it acquires it at once by evaporation.
The advantages gained by using a stronger bath of nitrate of silver do not, in my experience, counterbalance the increased expense. I shall, therefore, give the old proportions, 30 grs. nitrate of silver to 1 oz. of water, as being the most economical and giving the least trouble.
It is not necessary to protect this solution from the light. By careful filtration now and then it may be used for twelve months without having lost any perceptible strength.
Before I proceed further with the details of the process, it will be well to enumerate a few precautions. It is not necessary to have plate-glass, especially when the pictures remain on the glass; good flatted crown I have found to answer very well when small surfaces are to be covered. Any kind of glass, however, which is free from scratches or specks, will answer the purpose, although, when the pictures are to be removed during an excursion, a better kind of glass must be obtained, as a surface free from any blemish, and well polished, is indispensable, in order that the film may be removed with ease. With care the same glass can be used for a great number of pictures, if its polished surface is well preserved.
It is advisable to have the glass cut about half an inch longer than the drawing to be made upon it, as a kind of handle, to prevent the fingers touching the film. The collodion is not poured entirely over the glass—the upper portion is left uncovered 3 with this precaution a greater facility in working the process is ensured, and there is less fear of spoiling a good drawing with finger marks or other imperfections.
The next precaution has: reference to cleaning the plates of glass. After a time it will be found a source of much annoyance and failure, if great care be not taken to keep separate the cloths used in the various stages of the process. For instance, if, after fixing a drawing with hypo-sulphite of soda, the hands are wiped on any particular cloth, and it should be used afterwards for cleaning a plate of glass, there is every chance that the drawing made upon it will be spoilt; for the hypo-sulphite of soda forms with silver a sweet gummy salt exceedingly difficult to remove from the glass, unless it undergoes a thorough washing. It will be likely to produce a streaky deposit, which entirely mars the otherwise good effects of the picture, and unfortunately it cannot be discovered until the whole process is completed.
This inconvenience may not often oceur to those. who have an ample stock of materials, and can throw aside a number of plates of glass to be washed at leisure; but many who are limited in means, and consequently wish to make the most of a limited supply, cannot neglect this precaution with any hope of success.
In my own practice of the process, when on an excursion, I never take less than three cloths with me—one to remove the exeess of moisture from the glass, the next to partially dry it, and the third to give it the final polish, just previous to the preparation of the film; an old soft silk handkerchief will be found useful to give the last polish.
It will be well to keep the different stages in the manipulation of the process distinct from each other, in order to prevent confusion. They may be divided into five sections.
- The first division treats of the preparation of the film of collodion on the plate of glass.
- The second, the submitting the prepared plate to the nitrate of silver bath.
- The third, the exposure of the plate to the action of light in the camera.
- The fourth, the development of the image.
- The fifth, the fixing of the drawing, &c.