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.
Making The Exposure. With the Brownie or Ingento enlarging camera, they being always in focus, all that is required, after loading the camera with the bromide paper, is to carry it to the light with the negative covered with some opaque cloth, excluding all light until the camera is placed in a position with the negative end facing the light, when the cover may be removed from the negative and the exposure begun. The length of the exposure with the fixed focus enlarging cameras depends upon the intensity of the light and the density of the negative employed. With a good light and a negative of average density from 40 to 60 seconds may be sufficient.
570. With the Kodak No. 1 Enlarging Camera the exposure depends upon the strength of light, quality of the negative, times of enlargement, and the size diaphragm used with the average strength negative. If the small diaphragm is used from 20 to 30 seconds is usually sufficient ; if the large diaphragm is used 10 seconds will suffice.
Testing The Exposure. Until one becomes accustomed to judging the exposure required under the different conditions it would be best to use a test strip to obtain the proper exposure. Cut a sheet of paper into three strips. One of these strips arrange diagonally across the paper holder, and expose the strip exactly the same as you would a full sheet, and then develop. The exact time for development of a correctly exposed bromide enlargement cannot be given. The proper exposure, however, may be determined by the appearance of the image in developing. The image of a normal exposure will appear gradually, building up brilliantly and attaining full strength in about one minute.
572. Should the image develop up slow and appear dim and weak in one minute's time, you will know the paper is under-exposed. Should it flash up quickly, but appear dull and darken all over, in half a minute, you will know it is over-exposed. A correct exposure will develop gradually and grow stronger and more brilliant as it develops, until the shadows are clear and crisp. At this stage the print will be fully developed. After a few trials with the strips you will be able to judge quite accurately the exposure necessary. In some instances where the light is not very strong, or perhaps the negative is thick and hard, it may require two to five minutes for a full exposure. This can very nicely be determined with the trial sheets. After ascertaining the exposure necessary by means of the test strips, then load the holder with a full size sheet and give the same exposure. It would be advisable when you once learn the required exposure for a negative to note the time on the edge of the negative or on the negative envelope. This will save you making a second test when enlarging from the same negative at some future time.
Development. After the exposure has been made the next step is the development, which is accomplished in practically the same manner as the development of the plate or film, which, of course, is done in the dark-room. Provide a ruby or orange lamp, and three suitable trays, preferably made of rubber and slightly larger than the bromide paper employed. Bromide paper is not as sensitive to light as the dry plate or film; therefore a stronger light may be employed for developing. A small window opening in the dark-room, covered with two thicknesses of yellow post office paper, will answer; the ruby glass may be dispensed with and an orange colored glass employed; or even a plain piece of glass covered with two thicknesses of yellow post office paper will serve.