This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
Bromide Enlarging Briefly Described. Bromide enlargements from small negatives are obtained by exactly the reverse method employed in making the original negative. The original negative was made by means of a camera and lens, where the rays of light reflected the image through the lens into the camera, registering it upon the sensitive plate. Enlargements from a small negative are obtained by placing the negative in the rear of the camera, in the place formerly occupied by the plate-holder, and then permitting the rays of light to pass through the negative, then through the lens, and finally focusing on a sheet of sensitized Bromide paper, the size of the projected image depending upon the distance between the lens and the sensitized paper. The farther the paper is from the lens the greater the enlargement.
KNITTING Study No. 9-See Page 356 Mrs. Nancy Ford Cones.
570. The amateur who has not had previous experience in making enlargements may, at first, be puzzled to know why only particular kinds of sensitized papers can be employed for the work. He has learned to use printing-out papers and gaslight papers for contact prints and may be tempted to apply his knowledge of these to the extent of using them for enlargements. But for this work printing-out papers are entirely out of the question and gaslight papers suitable only when a very strong source of light is available-in other words, a sensitized paper, possessing much greater sensitiveness to light than printing-out papers, is needed, and for this reason, in contact printing, the paper is placed in, practically, optical contact with the negative. The light passing through the negative has full play on the paper and is not weakened by having to travel any distance.
571. In enlarging, the negative is, necessarily, at some distance from the paper on which the print is made. As light reduces in strength in the ratio of the square of the distance it has to travel, it requires a very much longer time, or a very much stronger light to create an image on paper which is at any distance from the negative.
572. Certain salts of silver, notably Bromide of Silver, are much more sensitive to light than others, such as Chloride of Silver, which latter is used in the manufacture of printing-out papers. Owing to the nature of Bromide of Silver salts it is utilized for such papers as are needed for enlargement work, which, as a general term are called Bromide papers.
573. Gaslight papers, which are a species of slow Bromide papers, can also be used for enlarging, but as their speed is roughly fifty times less than that of normal Bromide papers they require a fifty times longer exposure. Otherwise the handling of Bromide papers and Gaslight papers for enlarging is virtually the same.
574. Bromide papers compare in speed with very slow dry plates, consequently, need to be handled with all the precautions as to light fogging that are observed with dry plates-in other words, they must be used in a dark-room, under ruby or yellow light.
575. In the subsequent instruction the following methods of procedure for making enlargements are supplied: Using a regular enlarging lantern; employing an ordinary view camera used as an enlarging camera; using hand or pocket folding cameras; and professional methods such as are employed in studios, using the arc-light with and without condensers. We include therein, also, the use of the Aristo lamp. In all of the instruction we provide for the use of daylight as well as all kinds of artificial light, so that the reader may select any method described which will suit his or her convenience. An example of enlarging is shown in Illustration No. 7.
Illustration No. 7 Example of Enlarging See Paragraph No. 575.