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1. Media: Slides

Slide film is produced when reversal film (positive) is developed. Unlike negative film, slides can be viewed either directly or through a slide projector. Slide film is identical in format to the 35 mm film used in the motion picture industry.

Slides were used widely in the production of artworks from the 1960s to the 1980s and can be found in many museum collections. Since the emergence of digital photography, the slide medium has gradually been abandoned, with the industry halting the manufacturing of certain types of film and development laboratories becoming increasingly rare. This obsolescence has become an obstacle for institutions seeking to conserve the slide artworks they have acquired.

Storage of originals

Conservation practices for slides and film stock are already well established. Extensive documentation is available detailing and examining this type of information. It should be noted that the conservation of colour slides differs from that for achromous (black and white) slides, with colour being more prone to deterioration. Storage conditions therefore vary according to the type of slides being conserved.

Beyond handling, four controllable elements contribute to the deterioration of slides: temperature, ambient moisture, light, and pollutants. Severely damaged film cannot be restored. However, if the damage is noticed early in the deterioration process and the film is then conserved in optimum conditions, it can be preserved for many years without deteriorating further.

The colour image on slide film is produced using unstable organic dyes. The chemical reactions that create the image are ongoing, and storing the film at a low temperature helps slow this process. Controlling the ambient moisture is key to conserving the film. A slide subjected for a lengthy period of time to too high a level of humidity (above 90%) and without a sufficient air flow will be attacked by mould. Humidity destabilizes the dyes and changes the colours. Conversely, conserving slide film in dry conditions embrittles it and can lead to distortion. In addition, pollutants in the ambient air will further affect the film if the humidity is poorly controlled. [1]

Slides must be stored in a dark environment in storage containers made from neutral materials that will not affect the emulsions. Slides should not be enclosed in any type of sealed sleeve that prevents them from breathing. Certain practices have demonstrated that glass mounts placed on slides create a space that restricts moisture from escaping, leading to the appearance of branch patterns caused by mould. And while glass mounts are not recommended for storage, they offer protection against physical damage (dust, scratches, etc.) when the slides are being projected. These mounts also help keep the slides in focus, as they prevent the warping caused by the heat of the projector lamp.

Storing slides in Panodia [2] sleeves carries risks similar to those of using glass mounts, because the sleeves do not allow the slides to breath. If Panodia sleeves must be used, they should be suspended inside a storage unit (box, file cabinet). If not, physical pressure on the sheet could cause damage if the slides stick to it. [3] [4] For these reasons, it is best to avoid using glass mounts and Panodia sleeves to store slides. “Slide mounts can be cardboard, plastic or metal; however, none of these materials offers ideal protection. Plastic, open-frame mounts are acceptable.” [5]

While somewhat cumbersome, the Saf-T-Stor® [6] rigid storage sheets offer a very good storage solution. They have been designed to allow the air to freely circulate between slides while offering adequate protection. [7]

Optimal storage conditions for achromous (black and white) slides and film stock) [8]

 

Medium

Maximum temperature Relative humidity

Acetate

2 °C
5 °C
7 °C
20-50 %
20-40 %
20-30 %
Polyester 21 °C 20-50 %

 

• If slide storage in these optimal temperatures is not possible, keep in mind that the lower the temperature, the better the conservation.
• Temperature fluctuations should not exceed 2ºC over a 24-hour period.
• Relative humidity fluctuations should not exceed 5% over a 24-hour period.

Optimal storage conditions for colour slides and film stock [9]

Light and heat greatly contribute to the deterioration of colour film. Medium and long-term exposure to light dulls the image, with certain dyes deteriorating even when the film is stored in darkness. Storing colour film at a low temperature with controlled humidity appears to be the only way to decelerate the deterioration of colour film.

 

Medium Maximum temperature Relative humidity

Acetate

-10 °C 20-50 %
Polyester -3 °C
2 ° C
20-40 %
20-30 %

 

•  If storage in these optimal temperatures is not possible, keep in mind that the lower the temperature, the better the conservation. For example, the MBAC conserves its colour photographic materials in a vault where the temperature is maintained at 4°C. [10]
• Relative of humidity should not exceed 50%.

 

Projection

The projection of slides creates an environment whose extreme conditions have a negative effect on the film (elevated heat and lighting). For this reason, originals should never be used when a work is exhibited.

Duplication

One of the major challenges in the conservation of slides is the copying of original positives. Ideally, institutions try to obtain originals or sub-master copies of slides associated with a work during the acquisition process in order to make copies, which can then be used for exhibition purposes.

On June 22, 2009, Kodak announced that it was abandoning production of Kodachrome 64 positive film, [11] the last remaining product in its popular Kodachrome [12] line. Widely used for storage in museum collections, Kodachrome had the advantage of offering a much longer lifespan than all colour emulsions, even the most recent. Dwayne’s Photo, the last laboratory in the world to process Kodachrome film, announced it would no longer offer this service after December 2010. [13] This decision represents the end of a reliable and proven conservation solution that has also allowed for works to be exhibited.

Duplication of slides remains possible, because Kodak and Fuji, among other companies, continue to produce Ektachrome [14] and Fujichrome [15] slide film respectively, two products popular among museums. [16]

Two methods coexist for duplicating slides. Analog duplication is the conventional approach used in photography to reproduce slides with a duplicator. This is a tricky process, as the person carrying out the duplication must be subjective when adjusting contrasts and shades using special filters. Once the film has been exposed, it must be developed in the same way as the original was, and it is no longer possible to correct shading, contrast or clarity. While analog duplication is not complicated and it is still possible to have positives developed in a lab, the practice is nonetheless threatened with obsolescence by the rapid growth of digital photography.

Digital duplication is a hybrid process that combines analog and digital technology. The original slide is digitized using a scanner and saved on a computer. Each fundamental colour in the additive colour synthesis (green, red, blue) is processed separately, having been converted into a numeric value. This data can then be transferred to a given device for digital projection or re-converted into analog data to create a new slide.

The MBAC has used orthochromatic film to duplicate certain black and white slide works subjected to extended exhibition periods. This film has the advantage of offering much greater longevity and resistance to discoloration than conventional panchromatic film. Its heightened resistance allows for a significant reduction in the number of duplicates that must be made for a black and white work. Unfortunately, this film is also threatened with obsolescence. [17]

As explained by Ainsley Walton, [18] the cost of duplication may become a problem for institutions. A work that includes the projection of slides may be presented uninterrupted for a number of weeks on end; in such cases, the slides are subjected to heat and lighting conditions that can easily be described as extreme. Under these conditions, the slides deteriorate very rapidly and must be replaced regularly during the exhibition period, and this is why the institution must acquire a large number of copies of the same slides, which greatly increases the overall cost of the exhibition.

Given the imminent obsolescence of slide duplication and the high cost of this practice for institutions that own collections and wish to preserve and exhibit their works, it is interesting to explore new duplication options. Ms. Walton has related her experience in duplicating a work by Michael Snow. To reduce the cost of producing duplicates, the specialists in charge of preserving the work used 35 mm motion picture film stock[19] to create exhibition slides. This new strategy has the added advantage of reducing costs and opening a new channel for preserving slide duplicates. And while digital techniques are being increasingly used in the movie industry, it seems clear that silver-gelatine film will persist in this sector for many years to come. [20]

 


 

[1] Groupe de travail sur la conservation des collections du sous-comité des bibliothèques, Synthèse des normes applicables à la conservation et à la manipulation des documents sur support filmique et sur plaque de verre. Conférence des recteurs et des principaux des universités du Québec, 2001, available from http://www.crepuq.qc.ca/documents/bibl/Normes_films/normes_films.htm.
[2] Polypropylene storage sleeves made popular by Panodia.
[3] http://www.chassimages.com/forum/index.php?action=printpage;topic=19818.0
[4] Henry Wilhelm and Carol Brower, "Handling and Preservation of Color Slide Collections", in The Permanence and Care of Color Photographs: Traditional and Digital Color Prints, Color Negatives, Slides, and Motion Pictures (Grinnell, Iowa: Preservation Publishing Company, 1993).
[5] Loose translation of text taken from: Groupe de travail sur la conservation des collections du sous-comité des bibliothèques, 16.
[6] Saf-T-Stor® storage sheets are widely used in museums and archival institutions.
[7] Henry Wilhelm and Carol Brower, op. cit.
[8] Groupe de travail sur la conservation des collections du sous-comité des bibliothèques, op.cit.
[9] Ibid.
[10] Ainsley Walton during 2007 DOCAM Summit.
[11] http://www.kodak.com/eknec/PageQuerier.jhtml?pq-path=2709&pq-locale=en_US&gpcid=0900688a80b4e692
[12] The principle behind the development of Kodachrome film is very complex. The film itself has three superimposed layers, one for each primary colour (blue, red, yellow). Each layer is developed in succession. Kodachrome is characterized by true colours that are not over-saturated, unlike modern reversal films whose colours tend to be too bright. This high-contrast film with its impressive clarity offers a trademark appealing style, which is why it has been widely used by industry professionals in recent decades.
[13] http://www.dwaynesphoto.com/
[14] Unlike Kodachrome, Ektachrome is easier to produce and develop because of its similarity to traditional negative film. To date, Kodak has not announced any plans to cease production of its Ektachrome reversal colour film.
[15] The Fujichrome process is similar to Kodachrome, as it separates the colours in three phases.
[16] Henry Wilhelm and Carol Brower, op. cit.
[17] Orthochromatic photography refers to a photographic emulsion that is sensitive to only blue and green light, and thus can be processed with a red safelight. Using it, blue objects appear lighter and red ones darker because of increased blue sensitivity.
"Orthochromatic", Answers.com, available from http://www.answers.com/topic/orthochromatic-1.
[18] Ainsley Walton during 2007 DOCAM Summit.
[19] The 35 mm film format is the same as that used for slides; the film strip is simply cut and mounted into the supporting frames.
[20] Although many of today’s films are shot digitally, most cinemas are equipped with analog projectors; digital films are therefore transferred to analog film reels for screening. Moreover, stakeholders in the film industry (directors, producers, critics, etc.) show a strong artistic attachment to film and will continue to use this medium to shoot motion pictures.

 

Groupe de travail sur la conservation des collections du sous-comité des bibliothèques, Synthèse des normes applicables à la conservation et à la manipulation des documents sur support filmique et sur plaque de verre, Conférence des recteurs et des principaux des universités du Québec, 2001, document en ligne, http://www.crepuq.qc.ca/documents/bibl/Normes_films/normes_films.htm.