The plate covered with the iodized collodion is quickly transferred to a bath containing a solution prepared in the following manner:—Dissolve four ounces of nitrate of silver in eight ounces of water, and to this add twenty grains of iodide of potassium in one ounce of water; shake them together, and then pour the whole into fifty-six ounces of distilled water, and in half an hour add one ounce of alcohol and half an ounce of ether; agitate the whole and filter the next morning. The collodion plate is kept in this solution for a certain period, only learnt by experience, and should be occasionally lifted out to see if a uniform transparency is obtained; say that the immersion may be continued for five minutes, it is now ready for the camera, and may be exposed from about one to two minutes, or more if the light is deficient; the time of exposure is also a matter of practice, mere directions can be of no use in this stage of the process.
The picture is developed on a levelled stand, with a solution of three grains of pyrogallic acid in three ounces of water, to which sixty drops of glacial acetic acid have been added. When fully developed the plate is washed with water and fixed with a solution of hyposulphite of soda, consisting of one part of the saturated solution to eight of water, again thoroughly but gently washed, so as not to endanger the separation of the film from the glass; it is allowed to dry spontaneously, and being coated with amber varnish (a solution of amber in chloroform) is now ready to print from. It is, perhaps, hardly necessary to add, that the sensitizing and developing processes must be performed in a dark room.
Fig. 142.
a. Glass or gutta-percha bath to hold the sensitizing solution. b. Glass, with piece cemented on the end to hold the prepared glass plate, c, whilst dipped in the bath, a. The plate c has a cross in one corner to show prepared side.
Fig. 143.
First effect of peripatetic photography on the rural population.