OR DEVELOPING CHAM BER (Fr., Laboratoire ; Ger., Dunkel zimmer, Dunkelkamnser) A room or cupboard devoted principally to the operation of development, and from which all white or actinic light is excluded. Until A. J. P. Claudet patented, in the 'forties, the use of coloured media, preferably red, the devel oping chamber was really in total darkness ; but since then the name of " dark-room " has been somewhat of a misnomer.
The old idea that space is unimportant in the room used for developing is quite erroneous, particularly with respect to efficient ventilation, so necessary to the health and comfort of the operator. It is obvious, also, that greater con venience is secured when there is plenty of room for shelves and benches, and for moving about. Daylight, owing to its constant fluctuation, is not recommended, and does not add to the safety of the developing chamber, since sunshine or bright light tends in time to bleach non actinic fabrics and materials, and mischief may be done before this is noticed. It is preferable to block out all daylight and to rely entirely on artificial illumination. It is now realised that, provided the colour of the light is carefully chosen to match that region of the spectrum to which the particular plate employed is least sensitive, a much better illumination is per missible with safety than was at one time imagined, so long as the plate is not unneces sarily exposed to the direct rays from the lamp. The old-style dark-room, where the operator fumbled uncertainly in a dim, ruby glimmer, knocking over bottles and breaking glass measures in his inability to see a foot before him, is rapidly giving way to saner arrangements. In a properly designed developing chamber some means should be adopted for preventing the admission of light when the door is opened. One way of doing this is to have a double door, as indicated in the illustration which shows how a room 12 ft. by 8 ft. may be fitted up
as a dark-room. Another way is to curtain off a kind of alcove in front of the door, using a heavy opaque material.
An abundant and pure water supply is an important consideration if much work is to be done. Iron pipes should be avoided, as rust is objectionable in dealing with some sensitive surfaces. If a constant supply cannot be had, portable tank with ts tap or siphon, or even a couple of large pails, may be used. Swing rose taps should be fitted if possible ; ordinary taps are more troublesome, giving too forcible a jet and having a marked tendency to splash. But if an ordinary tap is provided as well, for use in filling bottles only, added efficiency is gained. The more shelves that can be fitted the better. Those which will hold the bottles or articles most frequently in use should be low down and well within reach. A small cupboard, with drawers to hold unexposed plates and papers, will be found extremely useful.
When a room cannot be kept permanently for developing, a bathroom, or even a cupboard, may be adapted temporarily for the purpose. If the work is done at night, and no outside lamps are near, there will be no need to obscure any windows that may be present ; otherwise a wooden frame may be made to fit closely in the opening, and covered with any opaque or non-actinic fabric. This is readily removable when not in use, and may be replaced in a few seconds. Portable dark-rooms of various kinds are obtainable, and some of these fold into a very small space. (See also "Dark-room Illumina tion," " Dark-room Lamp," " Dark-room Ven tilation," " Developing Bench," etc.)