Microfilming is the production of reduced images of documents by photographic processes. There are three main formats:

• Microfilm is usually 35 mm or 16 mm non-perforated film which can be presented as strips, rolls or cassettes. Monochromatic emulsions are commonly used but colour film is also available. 
• Microfiche is sheet film, usually 105 x 148 mm, incorporating multiple images – it is usually monochromatic but colour is also available. 
• Aperture cards, also known as image cards, consist of single 35 mm film frames mounted onto cards. This format is often used for reproducing architectural or engineering drawings.

There are three film composition types generally used for microforms:

• Silver gelatine or silver halide film is composed of silver salts in a gelatine emulsion on polyester film base. This is the preferred type for archival filming as it has excellent image and base stability when correctly processed. It will produce high-resolution images and a good tonal range. The image is black and white. 
• Diazo film incorporates light-sensitive diazonium salts in an emulsion. The image is usually deep blue to black and white, with medium to high resolution and available in all formats. The resilient outer surface of this film is less susceptible to scratching than silver halide film, making it very suitable for reference copies. However, it is chemically less stable and not suitable for long-term retention. 
• Vesicular film uses diazonium salts but the image is produced by tiny bubbles formed in a polymer layer when the film is exposed to ultraviolet light. The film is heat-processed, making it popular for quick and easy client copies. The resolution quality is less than diazo and silver halide, the image colour is in the pink to purple range, and all formats are available. It is normally used for reference copies or material for short-term retention, as the inherent instability of this film makes it unsuitable for archival filming. 

When film is being produced to create a permanent record, most standards and guidelines recommend that three copies be produced: a preservation master on silver halide film, a duplicating master (also silver halide) from which subsequent copies are made, and a set of as many reference or working copies as required (usually on diazo or vesicular film). The minimum acceptable requirement for archival purposes is one master and one reference copy.

All materials degrade over time. We cannot control this inevitable deterioration, but we can control how fast it happens. Certain materials are susceptible to deterioration in particular ways because of their properties, and other materials deteriorate as a result of particular environmental conditions.

Microforms are photographic transparencies or negatives and have the same problems associated with that type of material.

• Microfilming technology predates the 1930s and very old microfilm may be on acetate or nitrate-based film, which has particular preservation problems (see Protecting and handling photographs). 
• Some vesicular films produced in the 1960s and 70s were extremely unstable, resulting in severe image loss and liberating chlorine gas which can cause degradation of other records stored nearby. 
• Diazo and vesicular films can be particularly sensitive to high temperatures, affecting image quality. 
• Film which has been poorly processed or exposed to chemical pollutants in storage often develops a type of staining known as 'redox blemishes'. These are small deposits of metallic silver which interfere with image legibility. 
• Microforms can be badly damaged by exposure to dust, dirt and fingerprints, which spoil the image quality and may also act as a moisture absorbent and promote mould growth. Like most other photographic images, microforms are also light-sensitive.

As with any archival item, correct handling of microforms will aid in preserving them for as long as they are required:

• Handle with care. 
• Lint-free cotton gloves should be used at all times when handling silver halide film. 
• Silver halide master films should not be used for reference purposes as the film rolling mechanisms on the reader and printer equipment can cause severe scratching of the gelatine emulsion. 
• Regular surveys of the condition of film holdings should be programmed to monitor any problems, particularly to detect the development of redox blemishes. 
• Reference films should not be left in viewing equipment for long periods as prolonged light exposure will affect image quality. 
• Films and fiche should be returned to their protective packaging immediately after use. Do not leave microform material loose on a work surface where it could be easily damaged. 
• Viewing equipment should be well-maintained and in a clean work environment.

The method of packaging microforms will depend on the exact material and the use for which it is required. Master films should always be stored in archival quality enclosures to ensure their long-term stability. Reference copies may not require such stringent quality controls. The method of packaging will also depend on the specific format.

Microfilm

• Microfilm should be wound onto standard sized reels made from inert plastics or corrosion-resistant metals. The loose end of the film should be secured using a strip of archival quality paper held in place with cotton tape. Never use rubber bands or sticky tape to secure a film. 
• Each roll of film should be individually enclosed in close-fitting sealed containers made from polypropylene, polycarbonate or archival quality cardboard. The size of the container should fit the size of the film, ie do not put small rolls of film in large containers. 
• Never apply labels directly to the film – mark the outside of the container only. Some adhesive labels may damage films even when applied to the container, so marking with permanent inks is preferable. 

Microfiche

• Master microfiche should be individually enclosed in sleeves or envelopes made of inert plastics such as polyethylene, polypropylene, polyester or Tyvek, or archival quality paper. 
• Reference copies of fiche may not need individual enclosures as long as they are protected from excessive dust and light, eg in plastic file boxes or drawers. 
• Labels should not be applied directly to fiche or to individual enclosures and are usually not required as each fiche has its own header where control information is recorded. However, if additional labelling is required, use a permanent pen and mark the non-image area of the fiche (preferably in the header space). 

Aperture cards

• Aperture cards are normally only produced for reference purposes and can be stored as for reference fiche, in clean sturdy containers that exclude light and dust. The master copy would normally be retained as a roll film, however, if master aperture cards are held they should be individually enclosed, in the same way as master microfiche. 

The preservation master copy of any fiche or film should be kept in a different location to the duplicating master and reference copies. This should preferably be off site, even in another agency or state. This is a security measure to ensure that at least one copy of the information will always exist, protecting the master against destruction by theft, inadvertent use, or disaster such as flood or fire.

Storage furniture should be made of coated metal. Wood should be avoided, as it can release harmful vapours, can contribute to the spread of fire and may harbour insects. Specially designed storage furniture such as drawers and cabinets can be purchased for microforms allowing more efficient use of space, however, these are only necessary when large quantities of film are held.

Preservation and duplicating masters should be stored in a clean, dark, climate-controlled environment. Black and white material should be kept at 8–12°C and 30–40% relative humidity, and colour at less than 5°C and 30–40% relative humidity. Temporary records and reference copies can be stored under general archives standards of 18–22°C and 45–55% relative humidity.

Microforms degrade more quickly when exposed to ultraviolet light. Fluorescent tubes which are low in ultraviolet light should be used wherever possible in storage areas. Ultraviolet light can be easily measured with a light meter, and levels should not exceed 75µW/lumen. Lights should be turned off whenever possible. Storage areas should not have windows, but if they do they should be covered with curtains or blinds.

Insects and rodents once attracted to a records storage area may start eating the records, so:

• do not eat in storage areas 
• keep surfaces (floors, tops of shelves) clean 
• bait regularly for rodents and fumigate annually for insects

It is important to select the correct format and film type depending on the purpose for which the microform is required and the nature of the original record being reproduced. Take care that the filming process does not cause unnecessary damage to fragile or valuable originals. For this reason manual filming is preferable to automated filming.

Production standards are especially critical where microfilm is being produced to replace an original record that is inherently unstable and cannot be preserved. Preservation microfilming production standards encompass quality control issues such as document control, targets, camera settings, and post-production checks on image quality and chemical stability. Silver halide microforms produced and stored according to these standards are predicted to have a life expectancy of 500–1000 years, which very few record formats can match. However, films not produced to these standards may be severely degraded after as little as 20 years.

Please contact the Agency Service Centre for further advice on production standards if you are planning to produce microform copies of important records, or if you require further advice on protecting and handling microforms.

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