Machine for big contact black and white prints 1 ~ automatic timer 2 ~ black and white printing box 3 ~ antistatic cleaning cloth 4 ~ negatives 5 ~ contact black and white printing paper Photographers who employ large-size black and white film, 4 x 5 and up, frequently make final black and white prints in the darkroom as well as proof black and white prints by the contact method. For this purpose, they generally use a special black and white printing box with a built-in light source, which is more convenient than the simple hinged frame meant for proofs of small negatives. They will also need the materials shown at left: antistatic cloth to clean the negative, an automatic timer to control the exposure, as well as special contact black and white printing paper, which can range from 10 to 1,000 times less sensitive than the ordinarily used enlarging paper. The less-sensitive paper can be used because there is so much more light available to the paper. A 25-watt bulb shines up through a pane of diffusing glass, through the negative directly onto the paper. In operation the negative is placed emulsion side up on the glass, and a sheet of contact paper is laid emulsion side down over it. The hinged lid is then closed, and its underside of felt or rubber presses the paper tightly against the negative. Trial and error determine exposure time (for economy, small sections cut from a full-size sheet of black and white printing paper can be used in tests); two to five seconds are about right for a negative of average density. The black and white print is processed as usual - except that contact paper needs only about 50 seconds' development in the darkroom. The print box is able to print black and white pictures much more quickly than the enlarging method, and no focusing is involved in the darkroom. Unfortunately, control over the black and white printing of individual portions of the black and white image is harder to achieve. And, of course, the final black and white print will not be any larger than the negative is.