A Manual of the Collodion Photographic Process - Preparation of Collodion

Contents

Part 1

Part 2

PART III


Preperation of Collodion

It is not easy to give the exact proportions of gun cotton to be added to the rectified sulphuric ether to prepare the collodion solution, as this must depend entirely upon the strength and thickness required. In the ordinary way, it is better in the first instance to make a thick solution, and after having filtered off the insoluble portion of the cotton, to dilute the remainder when required for use.


It will be better for parties to depend upon their own experience after a few trials than to look for exact proportions in a recipe. By taking an ounce or two of ether, and adding the cotton by degrees, and well shaking between each addition, the solution can be tempered to any required thickness.


Also the thickness of the collodion must depend upon the skill and dexterity of the operator, and the season of the year.


In the commencement of the practice of this process the amateur should be careful not to use a very thick solution, especially if the weather be warm, as the quickness of the evaporation and the necessary slowness of his movements would render it unmanageable in his hands.


These considerations render it difficult to recommend any fixed and exact proportions, but whatever may be the thickness of the solution, great care should be taken to obtain a collodion, which will, when evaporated on a surface of glass, be sufficiently strong to bear removal when necessary.


This must be considered a most important point; for otherwise, if the film is weak, it cannot possibly be expected to bear the washings and various changes the operator may wish it to undergo.


The strength of this film can be tested in a general way, by pouring a small quantity on to a piece of glass, and when the surface has set a little, removing the film as a thin and delicate skin. This can be done by taking the edge of it between the fingers, and gently removing it from the glass.


If the collodion is sufficiently strong, it will bear in this way almost entire removal from the glass. The sensibility of the collodion to light is also very much influenced by its strength or weakness. And it may be considered as a general rule, within certain limits, that the weaker the collodion the more sensitive it will be to light.

In this view of the matter, it is consequently necessary to avoid the two extremes, of a very strong film or a very weak one.


The reason of this I will endeavour to explain. The quantity of solution of iodide of silver which a certain solution of collodion can be made to take up, depends in a great measure on the quantity of alcohol in the collodion; and it will be found that if the collodion is very strong, it cannot be made to take up much iodide of silver, but by adding alcohol, it is possible still further to iodize the solution. However, this can only be done by sacrificing the strength of the film, for the more alcohol you add to the collodion, the weaker it must become; and this arises not less from the addition of alcohol than from the much larger quantity of iodide of silver in the film, which the addition of the alcohol gives it the power of dissolving.