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.
Developing. The enlarged negative, as well as the transparency, can be developed in normal developer, with a little Bromide added. The Bromide will hold the shadows clear, and prevent fog, thus giving more snap and vigor to the negative. Without Bromide, even with the correct exposure, the negative is apt to be flat and weak. The latitude in enlarged negatives, especially where fast plates are used, is not so great as when photographing direct, because the contrasts between the high-lights and shadows are not so pronounced, as they all appear on a flat surface.
828. Negatives which vary in exposure, whether over or under-exposed, especially over-exposed, may be controlled in the developing if treated according to the exposure. (See "Developing Over and Under-exposures," Vol. II.) Enlarged negatives should always be developed a little stronger than smaller negatives. The Universal Pyro Developer, formula for which is given in Volume II, should be used, as the Pyro gives more color, thus producing better printing quality in the negative. This is essential, especially for large negatives.
Artificial Light. The same method followed in Bromide enlarging by artificial light may be used for negative enlarging, but more care must be exercised about the darkness of the room, as the dry plate is twenty times more sensitive than Bromide paper, and the least trace of actinic light will fog the plate. The placing of the transparency in the camera, the focusing and exposing, are exactly the same as for Bromide enlarging, with the exception that the dry plate does not require as long an exposure as Bromide paper; but the exposure for negatives enlarged by artificial light, should be four times as much as for daylight. (For detailed instruction regarding the use of artificial light see "Bromide Enlarging by Artificial Light.")
Making An Enlarged Transparency. With either of the methods employed for making the enlarged negative, an enlarged transparency can be made, and from this transparency, the large negative is made by contact printing. Where the small transparency was previously used for enlarging, you now use the original negative, and make the enlarged transparency in exactly the same manner as the enlarged negative. In exposing for the large transparency, give the same time as for the enlarged negative, and in developing, carry it a trifle farther than for ordinary negatives, thus allowing for the reproduction onto another large plate, thereby producing a new negative.
Making The Negative By Contact From The Large Transparency. To make the enlarged negative from this enlarged transparency, place the transparency in a printing-frame having good, stiff springs. Place the unexposed plate on top of this transparency, film to film. Cover the sensitive plate with a sheet of black paper and then clamp firmly. Be careful to dust both transparency and plate free of specks; also be sure that the back (the glass side) of the transparency has been thoroughly cleaned, as the least marking, or particle of dust or dirt, will show in the enlarged negative. It is advisable, in order to produce perfect contact, to use a soft pad between the unexposed plate and the back of the printing-frame. Unless the negative and transparency are in perfect contact, that part not in contact will be out of focus and appear blurred.