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.
Advantage Of Fine Grain Emulsion. The advantage of using a close-grain plate for the intermediate contact transparency for enlarging will be readily seen. With a little care in the exposure, good enlarged negatives can be made with the ordinary dry plate, and where Platinum paper is used for the printing surface, the grain of the negative does not show to any great extent.
"MARGUERITE" Study No. 13-See Page 357 Will II. Walker.
Making The Transparency By Contact. The transparency must be made in a regular dark-room, or in an ordinary room that can be made perfectly light-tight. Before entering the dark-room, however, clean the glass side of the plate of your negative with a soft cloth, and dust the film with a camel's-hair brush, removing all particles of dust. In the dark-room, under the light of your ruby-lamp, place this negative in the ordinary printing-frame. Then, take a dry plate from the plate-box and place it on the negative, film to film; next, place a sheet of black paper over the back of the unexposed plate, and clamp the back of the frame in firmly. Be sure that the springs are good stiff ones, so that the plate and negative are in perfect contact. To avoid the clear margin on the edge of the plate, caused by the rabbit in the printing-frame, use a frame one size larger than the negative. Use a thick glass that will fit the large frame, and support the negative. Be sure that the glass is thoroughly clean and free from bubbles or scratches.
Plates To Use For Making The Transparency. Special transparency plates are the best, but any ordinary slow plate will do. Rapid plates may be used, but they give less latitude in the exposure. Therefore, slow plates are recommended.
Exposure For Transparency. The necessary exposure will depend upon the speed of the plate, the strength of the light, and also the density of the negative. The exposure should be made by artificial light. A kerosene lamp, gas, or electric light, even a lighted match, are better than daylight. In fact it is almost impossible to make the exposure quick enough by even subdued daylight.
Using Ordinary Rapid Dry Plates. Hold the frame, containing the negative, about three feet from the light. If a 16-candle power electric bulb is used, a quick turning on and off of the light will give sufficient exposure. Two seconds exposure with a lighted match should be sufficient for an ordinary negative. The exact time can be determined after one or two trials. The better the transparency, of course, the better will be the large negative. Avoid over-exposure which causes fog. There is less danger of a fog with slow plates than with the regular plates, although when slow plates are not obtainable ordinary fast plates may be used, but more care must be given to the exposure. It is advisable, when rapid plates are employed, to hold the negative farther from the light, to avoid overtiming. The printing-frame should never be held less than three feet from the light, except when the exposure is made with a lighted match, in which case two feet from the light will be sufficient.
Developing The Transparency. When making transparencies from flat negatives, the contrasts can be increased by aiming at correct exposure (never over-expose) and developing strong. On the other hand, if the original negative is hard, give full time and develop normally to produce softness. Both the transparency and the enlarged plate may be developed in the ordinary way, using the regular Universal Developing Formula given in Volume II, but the transparency must be made stronger than for lantern-slide work, or regular direct exposures. Ordinary transparencies used for lantern projection, etc., must, of necessity, be very thin and full, with clear transparent shadows. Such a plate, if a negative were reproduced from it, would give flat, washy results, with no detail in the shadows. Therefore, when making transparencies for enlarging purposes, expose slightly longer than for lantern-slides, and develop to a good strength, using a little Bromide if you find that snap and contrast is needed. Unless the transparency has good strength the reproduction will be very flat and weak.