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Washing film

Don't underestimate its importance


Washing, a step in film processing that is as important as any other, removes residual fixer and soluble salts from the film. When properly carried out, it ensures good image quality and permanence.

The fixing process must be complete first. If it is not, no amount of washing will make the images permanent, and the negatives will stain over time. Thorough washing is essential to remove the fixing agent to avoid image fade and staining.

If your water supply contains rust, dirt or other impurities, a fine water filter should be installed on the water line to remove them. Water that has high concentrations of iron should not be used for washing.

WASHING TIME

The time needed to properly wash film is dependent upon:

  • water temperature;
  • chemical contamination; and
  • the rate of water change.
  • Temperature - Water temperature for washing film should not exceed 75 degrees F (23.9 degrees C.) since it swells the gelatin and can damage the emulsion. The temperature range best suited for washing film is 60 to 75 degrees F (15.6 to 23.9 degrees C.), and more washing time is recommended for temperatures in the low end of this range than for the high end. Ideally, the film washing water temperature will be similar to the temperatures of the other film processing solutions.

    Chemical contamination - Chemical contamination of the washing water can occur in a number of ways, all of which can be avoided.

  • If your washing water contains negatives that are partially washed and you add a new negative straight from the fixer, you have contaminated the washing process and must start the washing process over again for both negatives.
  • You can contaminate the wash water if you have processing chemicals on your hands when you place them in the wash tank.
  • Accidental spillage of chemicals in the wash tank will require starting the washing process over.
  • The rate of water change - The average negative releases about half of the hypo contained in its emulsion in one minute when in direct, uninhibited contact with fresh running water, and half of the remaining half (i.e. a quarter of the original amount) after another minute, and so on, reducing the remainder by half every minute until the amount of remaining hypo is negligible.

    The minimum washing time for negatives in fresh running water that is completely changed every three minutes is twenty minutes. If the water is completely changed every five minutes, then thirty minutes of washing is enough for most films. Agitation and the use of a rapid film washer designed for washing film with a constant exchange of water can bring the washing time down to five minutes.

    You are better to be safe than sorry, so if you are uncertain whether your film is satisfactorily washed in, say, ten or fifteen minutes, then allow the washing process to continue for another five minutes or so.

    HYPO CLEARING AGENT CUTS WASHING TIME

    You can save a great deal of water and time by using Hypo clearing agent, an optional chemical that many people use when processing black and white film.