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WRS MOTION PICTURE AND VIDEO LABORATORY |
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1000
Napor Boulevard,Pittsburgh Pa 15205 |
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WRS MOTION PICTURE AND VIDEO LABORATORY |
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1000
Napor Boulevard,Pittsburgh Pa 15205 |
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Storage of Motion Picture Film
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Storage Conditions Recommended storage conditions for processed film will vary with the type of film and the anticipated length of storage. Actual conditions will usually represent a compromise between optimum for each component of the film, i.e. base, emulsion, color, B & W, an the cost of achieving the desired condition. Film Conditioning The rate of conditioning depends on the thickness of the film that is available to the air, the temperature and air velocity. A single layer of acetate film of normal motion picture thickness (.006) freely exposed to circulating air reaches equilibrium in approximately one hour. The same film wound in a 35mm x 1000ft. roll at 24 ounce tension takes approximately four weeks. Two alternate methods of conditioning film are suggested: 1. Wind the roll onto a loop rack and leave it for the specified time in a conditioned room 2. Put the roll through a conditioning chamber having controlled air velocity, temperature, and humidity. Extended-Term Storage of Color Safety Film Preprint material consisting of multiple layers containing dye images should be kept as cold as possible at very low RH. The following table from the Kodak publication, The Book on Film Care, indicates influence of temperature and humidity on dye fading.
As indicated by the table, storage at 15% RH cuts the fading rate in half, however, it also increases the chance of brittleness and emulsion cracking. Therefore, a compromise condition of 20% to 30% is recommended. The temperature table indicates that storage at -26° C (-15° F) cuts the fading rate to 1/1000, however, the cost of maintaining such a refrigerated storage condition may be prohibitive. A different approach would be to condition the film to 25% RH and to hermetically seal it in a container that would protect it from the ambient RH of the storage area. Film conditioned in this manner can be stored in cold areas having relatively high RH, such as mines and caverns. This type of seal will also protect the film from dust and chemical fumes in concentrations usually found in underground storage areas. While this type of storage will maintain the films RH and protect it from dust and chemical fumes, it will accelerate the reaction if Vinegar Syndrome occurs. Extended-Term Storage of B & W Safety Film Black and white films on acetate and polyester base should be stored at 70° F and 20% to 50% RH. If protected from high RH as described above, these materials can be stored in areas having a considerably lower ambient temperature. Active Working Storage For an active working storage area, a controlled temperature of 75° F, 40% RH is satisfactory for both color and B & W films. Film can be in untaped cans stored flat on racks. This material will not require additional conditioning before printing if it is in equilibrium with the storage area. Extended-Term Storage of Nitrate Film Most preprint material on nitrate base consists of a silver image. While early color processes often used dye images for release prints, the preprint material consisted of one or more silver images. Therefore, storage areas for nitrate base film color or B & W require the same physical conditions. Ambient temperature should be below 50° F and RH between 40% and 50%. Lower RH would retard decomposition, but would increase brittleness. Active Working Storage of Nitrate Film Temperature and RH conditions for a working vault should be below 70° F and between 25% and 60% RH. All nitrate base film in either a working or archival status must be stored in an approved vented cabinet or vault. Standards for the construction of approved storage areas have been established by the National Board of Fire Underwriters. Recommendations for meeting these standards are outlined in N.B.F.U Pamphlet 40, obtainable from N.B.F.U., 85 John Street, New York, NY. Examination and Evaluation of Existing Material Before storage, all nitrate base film should be carefully examined to determine its condition. Visual examination of nitrate film will detect major physical difficulties, but decomposition will be detected only after some damage has occurred. The sense of smell is more useful in detecting the earlier stages of nitrate decomposition because the nitrogen oxide fumes given off have a characteristic pungent odor similar to that of nitric acid. If any signs of decomposition are present, it should be cleaned, duplicated on a safety base film and then destroyed. Nitrate base film still in good condition should be cleaned if necessary and each roll place in separate film can. Aluminum or stainless steel is preferable to tinned steel. Cans in which nitrate base film is stored should never be taped or otherwise sealed, as this would prevent the escape of nitrogen oxide gas, which accelerates decomposition of the film. Care should also be taken to insure that no acetate or polyester base film is stored in the same can as the nitrate film. Unstable or decomposing nitrate film produces nitrogen dioxide gas, which has a three-fold effect on acetate film. The first stage discolors the starts to fade the image, then the gelatin of the emulsion is attacked and degraded and finally the base begins to decompose. A simple and effective method of rapidly distinguishing between intermixed nitrate and acetate base films in a single roll is to view the edge of the wound up roll with an ultraviolet lamp. The nitrate base film appears black and the acetate appears bluish purple. Another method of identifying nitrate base film is to check the visible frame line mark on processed film. The frame mark is orientated lengthwise between the perforation on safety film and widthwise between the perforation on nitrate film. The final conclusive test of nitrate versus safety film is a burning test that can be made safely if certain precautions are taken. Cut a piece of film approximately 16mm wide and 35mm long. Bend the film lengthwise and crease it sufficiently so that, when released, it will stand upright. Stand the film with the crease vertical on a flat surface. This should be a safe distance from all film stocks. With a match flame, ignite one of the top corners of the film. If the film ignites easily, burns down rapidly and vigorously with a bright yellow flame, and is completely consumed in less than 15 seconds, it probably is cellulose nitrate. If it ignites with difficulty and takes more than 15 seconds to be completely consumed, it is probably safety base film. Each roll of safety film should be visually examined on rewinds. Such a check will reveal major physical difficulties such as fluting, buckle, twist, curl, spoking, fungus growth, or severe color fading. Film that has been properly stored will exhibit a minimum of these effects. Film that has been subjected to extreme variations in temperature and humidity could exhibit several of these defects. All films, color or B & W, can be damaged by mildew or fungus growth. When film is stored for any length of time at RH above 60%, some fungus is likely to grow on the surface of the emulsion or support. If discovered in time, steps can be taken to remove it. If the growth has gone too far, it may have caused permanent damage to the image. Water or water solutions should not be used for the removal of fungus growth because such growth on the emulsion side causes a solubilizing of the gelatin. The use of water or water solutions will lead to disintegration of the image. When the gelatin has become etched or distorted by the fungus growth, there is no satisfactory method of restoration. Removal of Film or Magnetic Tape from Extended-Term Storage Film and tape stored at reduced temperatures must be allowed to warm up until its temperature is above the dew point of the ambient air before the package or can is unsealed; otherwise moisture will condense and spotting may occur. Moisture condenses on an object if its temperature is below the dew point of the surrounding air. In summer, the dew point may reach 75° F in temperate climates and 90° F in tropical climates so that materials stored at 40° to 50° F dry bulb may have moisture condense on them when removed to the outside air. Under these conditions, condensation occurs readily on glass, metal, film base, or other non-porous material, but is generally not visible on cardboard boxes, corrugated cartons, etc. This is because the paper absorbs the moisture as rapidly as it condenses and water droplets do not have time to form. Any moisture condensation that may occur inside a sealed container is harmless because the amount of water vapor the air contains is infinitesimal. The possibility of damage from condensation occurs after the container is removed from refrigeration and opened exposing the film to large volumes of moisture-laden air. Moisture condensation on film taken from refrigerated areas can easily be prevented by allowing the container to warm up above the dew point of the ambient air before it is opened. The amount of time required depends on the thickness of the package, how well it is insulated, the temperature difference, and the dew point of the outside air. Usually the shipping preparation time plus the time in transit and receiving at the laboratory is sufficient. The approximate warm up time necessary for film packages to avoid moisture condensation after removal from cold storage is twelve hours for a carton of ten 1000 ft. x 35mm rolls for a temperature rise of 25° F or thirty hours for a temperature rise of 100° F. A safe procedure would be to instruct the laboratory to hold the film for twenty-four hours before opening the cartons. Film Storage - Water Protection The useful life of film can be shortened significantly by contact with water such as from floods, leaky roofs, burst pipes, or fire sprinkler discharge. Storage racks should be raised so that the lowest shelf is at least 6 inches off the floor. Drains provided should have adequate capacity to keep water from a sprinkler discharge from reaching a depth of 3 inches. If the film storage area should become flooded, prompt steps should be taken to reclaim any films that were immersed. Once the film has become wet in the roll form, it should be kept wet. If it dries, even partially, it may be impossible to unwind it for cleaning because the convolutions have stuck together. If there are no local facilities for re-washing and drying the film immediately, the film should be placed in a water-filled container and sent to a laboratory where it can be washed and dried properly. For holding wet or muddy film prior to the cleaning operation, the roll should be immersed completely in a cold water solution (below 65° F) containing sodium sulfate and formaldehyde. This will prevent the convolutions from sticking together and the growth of bacteria. It will also help prevent swelling and softening of the emulsion, which are major causes of damage.
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