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.
429. Quite unsimilar to the papers described in the previous chapters are the so-called developing or gaslight papers. The first name is given to these papers because the image has to be developed on the paper in the same way as on a plate or film, there being no visible image after printing. They are called gaslight, first because the paper may be printed by gaslight or artificial light and, second because these papers, being of considerable less speed than a dry plate, do not require the use of a dark-room in order to develop the image, but can be worked in a room lighted with gas or other artificial light, without affecting the image. As these papers are very much more sensitive to light than printing-out papers, they must be kept in light-tight boxes or packages; and the placing of the paper on a negative to be printed from must be done in subdued artificial light.
430. With gaslight paper, the photographer who is making pictures whether for pleasure or for profit, and who may be following his usual vocation during the day and spending his evenings and spare moments only at this pleasant and profitable profession, is enabled to make prints by oil, gas or electric light. There is no waiting for sunshine, which is the case when making prints on a printing-out paper.
431. There are many brands of developing papers. The most popular are the Velox, Azo, Argo, Cyko and Artura.
Each brand is made in at least two grades, regular and special.
432. All manufacturers place their products on the market, in cut sheets to suit the different sized plates or films used. There are twelve sheets to the smallest package, although the paper is put up in two dozen, half gross and gross packages, as well.
433. To meet the requirements of the printing qualities of all kinds of negatives, gaslight papers are manufactured in various grades of paper and emulsion, but in this instruction we will only treat with the regular grades. The special grades are dealt with in the advanced instruction on printing, Vol. IV.
Developing Powders. There are many prepared developing powders which can be procured, and each manufacturer claims that his brand is the best for his particular paper. There is a certain amount of truth in this; yet, with the exception of a slight difference in the proportion of the various ingredients, all developers are practically the same. All contain a developing agent, such as metol, ortol, hydroquinon, etc., also sulphite of soda, either potassium or sodium carbonate, and bromide of potassium.
435. The developing powders should be dissolved in a given amount of water and then placed in a bottle, corked and labeled. When ready to develop, pour from the bottle enough of the developer to fully cover the print. The used developer should be saved and poured into a separate bottle. A little fresh stock solution added to the old bath the next time you are developing makes it as good as new.
436. The beginner can make no mistake in using these prepared developing powders, but he must carefully mix ac-
Developing or "Gaslight" Papers - Regular Grades. 237 cording to the manufacturer's instructions printed on the package.