PhotographyTips.com - the #1 guide to better conventional and digital photography Become a Member iPhone Posing GuideGuide to Posing the Female Model BookGuide to Posing the Model CD
Search
Login

Member Login

Find us on Facebook
Follow us on Twitter
Find us on Flickr
Connect with us on LinkedIn

SPONSORS

Sell Photos Online

FEATURED SITES


Drying film

Not too fast; not too slow - in clean, dust-free conditions


The last stage in the processing of black and white film is to dry the wet negatives. The drying stage contains two steps. The first is to physically squeeze water from the negatives just after you remove them from being washed in the development tank. The second step is to hang the film so that evaporation can complete the drying job for you. (Note that the use of a wetting agent before drying will help to avoid common problems, such as water spots, in drying.)

When drying film, precautions must be taken against:

  • uneven drying;
  • contamination by dust in the environment;
  • scratching the film;
  • accidental contamination by darkroom chemicals;
  • film damage by improper handling; and
  • overheating, which can damage the films emulsion and also cause the film to curl.
  • STEP 1 - PHYSICALLY REMOVING EXCESS WATER

    Following completion of washing, allow the wet negatives to drain by holding them above the sink or tank for 20 to 30 seconds. With the film completely removed from the reel, draw it upwards in one continuous motion between the tongs of a film squeegee that you have slightly-dampened with wetting agent, or between your index and middle fingers, to gently squeeze off surface moisture. Be sure your hands are free of chemical contaminant and dust-free, and also slightly moistened with wetting solution.

    STEP 2 - EVAPORATION DRYING

    Attach a film clip to one end of the negative strip, then hang the clip from a rod or line sufficiently high above the sink or another waterproof surface so that droplets draining from the film will not cause water damage to anything below. This form of drying is similar to hanging of laundry on a wash line outside except that, since roll film tends to curl, you should attach another film clip at the bottom of the negative strip as a weight to prevent curling.

    FILM DOES NOT DRY UNIFORMLY

    Although recently-developed film may at first glance look to be the same over its entire surface, the newly-made, wet negatives have characteristics that may cause them to dry unevenly. Dense negatives or negatives that have particularly dense areas contain less water and therefore dry more quickly than thin negatives. This is because the greater concentrations of metallic silver in the denser parts of the negatives dont absorb water, but the thinner-density gelatin around them may have a lot of water in it. Therefore, thinner-density areas require more time to dry than denser areas that have less water in them.

    PROPERLY-DRIED FILM SHOULD BE FLAT

    Not only are negatives already drier in areas of higher density, but they dry more quickly at their edges and corners. These differentials across the film may cause unwanted curling, since strain is placed on the negative when uneven drying occurs too fast.

    The rate of drying and the amount of curl depend upon how thick the emulsion layer is and whether the film has a backing of gelatin. If the emulsion layer is thick, drying will take longer. If the film has a gelatin backing, drying will also take longer, but the gelatin layer creates opposing strain as it dries that causes the negatives to curl away from the emulsion layer, resulting in a flat negative when dried.

    The aim is to dry the film at a rate that creates minimal strain. Film that is hung to dry at normal room temperature will usually dry fairly uniformly since the amount of moisture in the air around the film (the rooms normal humidity) acts as a controlling factor. In fact, when it is too humid, it can cause the film to dry too slowly or even stop drying since a negative must be surrounded by drier air in order to dry, an effect that can be overcome by causing the air to move away from the film so that humid air is replaced by drier air that makes the film dry more quickly.

    HEAT HELPS NEGATIVES TO DRY

    Heating the ambient air will also speed up drying, since heated air accepts more moisture than cold air. But, you must be careful not to overdo it. Too much dry air around the film will cause moisture at its surface to evaporate more quickly than it can be replaced by the movement of moisture through the film itself. When water leaves the films surface more quickly than it can migrate through the film to the surface, you risk damage to the negatives.

    Special film-drying cabinets are available in which heat, air flow and humidity can be controlled. Warm air is directed to the surface of the film, where it picks up moisture and moves out of the cabinet to be replaced by more warm, dry air to continue the process. In tropical and other humid climates, where the ambient air is saturated with moisture, the air must be dehumidified before it reaches the film. In arid climates, control must be exercised so that drying does not occur too quickly. Heat and air flow must be reduced so that there is a balance that suits the ambient conditions and the films moisture content.

    An indicator that the negatives are dry occurs when when their emulsion side has become slightly concave (curved like the interior of a circle).

    WHAT HAPPENS IF NEGATIVES GET TOO DRY?

    If a recently-developed film becomes over-dried, it curls toward the emulsion and can even become brittle and susceptible to damage.

    HOW DO YOU KNOW IF NEGATIVES ARE DRIED PROPERLY?

    Properly-dried negatives have surfaces that are not moist to the touch, but that are firm and soft enough that damage doesnt occur when the film is flexed.