EQUIPMENT OF THE DARK-ROOM 252. The Amateur's Dark-room. There is no need of a specially equipped dark-room for the production of good photographs. Any room (preferably kitchen or bathroom containing a sink and running water) may be used after dark as a photographic " dark-room " without alteration. If the room faces a lighted window or if there is a light outside (e.g. a street lamp), all that is necessary is to close the shutters or draw the curtains ; failing this, some dark fabric must be hung so that it fits tightly over the window ; any light that filters through the cracks will not matter as long as the sensitive films are not exposed directly to it.
The amateur who has sufficient leisure and opportunity to work during the daytime requires a non-actinic light, and can fit up, according to his resources, a dark-room similar to that of a professional photographer. Directions are given for this in §§ 254-261.
253. Public Dark-rooms. The public dark room, found chiefly in hotels, is designed entirely for the changing of slides and changing boxes to the exclusion of all other operations (the dark-rooms of amateur photographic societies, in which the equipment is similar to that of a professional, obviously do not come in this category). The function of a public dark-room being thus limited, a cabin not much larger than a telephone box is quite sufficient (about 4-A X 4 X 7 ft.) The equipment consists only of a small table along one wall to a depth of about i8 in., and a waste-paper basket. A table standing about 3 ft. from the ground will be convenient, and a stool of appropriate height will enable one to work sitting down. The room must be perfectly light-tight, no ray of light being visible after remaining 5 minutes in total darkness. To ensure this, it is usually necessary to provide a rebate or seating for the door to the width of an inch or two, the seating thus formed being painted matt black. A catch on the inside permits the occupant to shut himself in. The inside is papered or painted a light yellow or orange colour. The red light must be placed so that it does not illuminate the table directly, only by light reflected from the walls. The best plan is to provide a small window in one of the walls about i5 x 20 in., fitted with
non-actinic screens, the source of light being placed outside the room ; this prevents the lamp being left on after use by mistake. A mov able shutter, worked from the inside, shuts off the light completely when using panchromatic emulsions.
254. Construction of the Ideal Professional Dark-room. The first consideration is the health and safety of the worker.' Do not let the dark room be so large as to lead to its subsequent conversion into a lumber-room.
Most solutions of salts, particularly the con centrated solutions of hypo used for fixing, cause disintegration of cement. The floor of the dark-room, at least in the working space, should preferably be paved (earthenware tiles, not cement, jointed with bitumen), asphalted, or covered with some impermeable composition. If the floor is of wood, it should be entirely covered with a rubber covering or linoleum, cemented down, or, at least, rendered imper meable by pouring hot paraffin wax over it, the excess of wax being scraped off before cool ing (the coat of paraffin wax should be renewed from time to time).
The interior walls, and, if possible, the ceiling, should be covered with a washable paint, prefer ably matt (many water paints withstand water after complete drying) of a light colour—but not white, as it gets dirty so easily, and occasions reflections, which may cause trouble when the dark-room is used for enlarging. Yellow and orange are the most suitable. They remain light whatever illuminant is used (red or green). It is well to cover the wall at the back of the sink with earthenware tiles or thin sheet lead to protect the wall from splashes.
If possible, the dark-room should have a window for ventilation when the room is not in use. The easiest way of excluding light is to replace the panes of glass by tin plate ; or a blind may be fitted between two frames, forming a trap for the light ; or a detachable shutter may be constructed by gluing opaque paper on cloth stretched on a framework, which, in turn, Failing any of these devices, it should be borne in mind that it is much easier to render completely light-tight a sliding door than one of the ordinary pattern on hinges.