MANIPULATION OF THE COLLODION PROCESS.
THE description I am now about to give of the manipulation of the process has reference to no particular form of apparatus or camera ,it is applicable to all. I have purposely kept the manipulation distinct from the general remarks and formulae included under each division of the subject in the foregoing pages. The subject-matter, however, will be divided in the same way, each heading being of a similar kind, so that reference can be made from one division to the other. Thus the description of the manipulation will be carried on without being too much prolonged by the insertion of matter not having immediate reference to the working of the apparatus.
ON THE CLEANING OF GLASS PLATES.
AFTER the preparation of Iodized Collodion, the next matter to be attended to is, the procuring of clean glass to operate upon. This matter may be considered a division of the process, and is of much more importance and exercises more influence on the results of the operator than is generally imagined. Many pictures have been spoiled, which otherwise would have been good specimens of skill, by the want of due care and attention in the choosing and proper preparation of the glass plates.
Little care is necessary in cleaning new glass for the first picture, except washing it in water, and drying with a cloth. I must first remark, that patent plate glass has very often numbers and figures marked upon it, generally with soap: these marks will often give a permanent impression, and show themselves in every picture by an excess of development in those parts, if that side is incautiously used.
These marks, although they can be washed off, apparently leave a permanent stain; in fact, the polish underneath is corroded and destroyed. This defect in the polish of the glass leads to the consideration of another evil of a similar character, which arises from the use of glass upon which pictures have been made and allowed to dry. It is almost sure to cause imperfection in the picture, and should be carefully avoided.
After fixing a picture, examine it to ascertain if it is worth preserving. If it is found not good enough to keep, wash it off the glass before it has had time to dry. The same piece of glass can be used a great number of times, with this precaution. The want of due caution in this little matter has been the cause of numberless failures with many operators.
Thin patent plate glass is the best kind at present in use, but it has one defect, its colour is too green; consequently, it gives an unpleasant tone to positives, which, being looked at through the body of the glass, are affected by it. It would be a great advance if a white glass with the same polish and flatness could be procured. The next glass to patent plate is flatted crown. It is much cheaper, and very thin; one side of this kind of glass is highly polished, and well adapted for the purpose, but the other side should be avoided; it is rough and gritty to the touch, with a slight haze upon it; the difference between the two sides is easily detected; very often merely passing the finger over it will be sufficient, or examining it in a good light.
Sheet-glass is now made very clear and flat, and is often sold for flatted crown. It is more equally polished on both sides, but it is liable to be specky and rough in places, and the polish generally is more defective; this kind of glass should be avoided if possible. Specks, or scratches of any kind, are liable to produce defects in the picture; consequently, the glass should be examined, to choose the best side previous to covering it with collodion.
The best method of cleaning glass is with a mixture of tripoli and spirits of wine; the two are mixed to the consistency of a thin mud, and applied to the glass with a rubber formed with a piece of cotton velvet tied over a bundle of cotton wool. A small quantity of the mixture of tripoli and spirits of wine is poured on to the glass, which is rubbed briskly with the velvet rubber, and afterwards finished with a piece of velvet, kept clean and free from dust for the purpose.
Before pouring the collodion on the glass, its surface should be freed from any adhering dust or fibre, which are often attracted by and cling to the glass just after it is polished. It is better to clean a stock of glass previous to commencing operations, preserving it from dust in a grooved box. If the glass is cleaned just as it is required, the dust raised during the operation is very likely to settle upon the glass during the time it is being coated with collodion, causing thereby an imperfection in the film. It is often a want of caution in these little matters which retards the progress of the operator, and constitutes the difference between a careful and a careless manipulator.
The glass plates when they are first cut have a clear and sharp edge, to which the collodion will not cling; the edges of both sides should he roughened by passing them over a grindstone, or by drawing down the sides briskly a slip of glass; the latter method effectually breaks down the clean sharp edge of the glass.
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