For these and other reasons I strongly recommend the use of yellow light, a thoroughly safe one being given by gas or lamplight passing through one sheet of yellow glass and one thickness of "canary medium."
This light, while being absolutely safe, gives such perfect illumination that it is as easy to control and estimate results as it would be by ordinary unfiltered gaslight.
If a ruby glazed lantern is already in use for negative work, it can readily be prepared for bromide printing by merely removing the ruby glass and substituting the yellow and canary medium. With these brief hints as to illumination, let us consider the entire process in its various stages.
Unpacking the Paper.—The sensitive paper is generally packed in envelopes sufficiently opaque to protect it from the admission of light. The packet must be opened in the dark-room from which all light (even stray streaks beneath the door) is excluded, excepting only that given by the yellow glazed lantern. The outer envelope being carefully undone, an inner cover will be found and these wrappers should be placed on a dry table while a sheet of the paper is removed.
It is a good plan to have a "light-tight" box (obtainable from any dealer) in which to put the paper after unpacking it; this prevents loss of time and awkwardness of handling in having to replace the paper in its wrappers each time a piece is withdrawn for use.
When several prints from one or more negatives are required, it is an excellent thing to have two of these boxes, one for the unexposed paper and one in which to put the prints as made until all are ready for development.
The Class of Negative.—Bromide paper gives us a great command over results; in fact, so vast is the control we may exercise that it is possible to secure good results from almost all classes of negatives, from mere ghosts to those with density almost equal to that of a brick wall. But there is, of course, a class of negative that gives a good result with the least expenditure of skill, such a one is generally known as of average density, having a full scale of gradation with high-lights dense, yet not so opaque as to prevent you seeing a window clearly defined when looking towards it through the densest parts of the film, such as the sky, for instance. Another way to test the density is to put the negative, film side down, on some large print on white paper, the large letters should be just visible through the sky, but the smaller print should not be readable.
That is the class of negative usually considered in Instructions for Use, as an "average" negative.
The Sensitive Side of the Paper.—A difficulty sometimes occurs in telling which is the sensitive side of the paper: this may be easily ascertained by the appearance of the edge, which turns slightly inwards towards the sensitive side. This is quite apparent to the sense of touch as well as sight. Some people moisten their finger and thumb and squeeze the paper and see which sticks (the sensitive side), but that is a dirty method and quite unnecessary.
Printing from the Negative.—Having unpacked the paper, after making sure that all but the yellow (or ruby) light has been excluded from the room, we are ready to print.