The Conservation of Colour Slides

Blog post by the Putting Flesh on the Bones Project Conservator Vanessa Torres. A trained paper conservator Vanessa works at the National Science and Media Museum, and acts as secretary for the Photographic Materials Committee at the Institute of Conservation.

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Image 1 – Variety of different frames in the Calvin Wells Archive

In September 2018, I had the opportunity to attend a 2 day workshop on the conservation of colour slides at the Faculty of Sciences and Technology the New University of Lisbon. The workshop was organised by the Portuguese art conservation organisation NEON and was conducted by Katrin Pietsch and Lénia Oliveira Fernandes; specialist photograph conservators from the Nederlands Fotomuseum. The event was divided into both lecture and practical sessions which provided a one-on-one learning experience for the attendees.

During her lecture Katrin discussed how the Nederlands Fotomuseum had raised funds for the Eye Love You conservation project by directly engaging with various stakeholders, such professional photographers, photography enthusiasts and the general public. The Eye Love You conservation project, aims to conserve the archive of one of the Netherland’s greatest and most influential photographers Ed van der Elsken. In her talk Katrin explained that van der Elsken kept his archive at his home in Edam where it had been inappropriately stored. As a result of the varying temperature and humidity, the 45,000 unique colour slides were damaged by mould.

If mould is allowed to grow on photographs, it gradually eats away at the emulsion and image. The only way to remove the mould permanently is to clean the pictures one by one. The conservation studio at the Nederlands Fotomuseum has developed a special method for doing this.

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Image 2 – Lecture’s presentation showing the house of Ed van der Elsken where he kept his collection throughout his life. Detail of mould growth in slides from his archive on the right.

Slides are positive transparencies which unlike other photographic processes do not require the use of negatives. Before the rise of digital photography, positive transparencies were a popular medium as it allowed the photographer to see a positive image with the aid of light box or projector. Similarly transparencies were commonly used for educational or commercial purposes, allowing for lecturers or speaker to project images and content during lessons or presentations.

The materials used to construct slides changed over time; the outer frame made from metal, plastic or paper and the support which holds the image was initially made from glass before plastic. The image itself is embedded in an emulsion layer which is laid across one side of the support. This emulsion is made out of gelatine which is a source of food for mould. In the right environmental conditions and with a constant food source mould can proliferate rapidly.

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Image 3 – Dismantled slide and its anatomy from the Calvin Wells Archive at the University of Bradford

In 2016, Lénia joined the Eye Love You project with the aim of carry out and completing conservation on the van der Elsken Collection within a period of 2 years. During the lecture, Lénia explained the great variety of photographic film and frames found in van der Elsken’s archive (40 years of body of work). It was fascinating to learn the frames themselves can be used as dating tools.

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Image 4: Lénia presenting her findings on dating slides based on the information gathered from their frames

Ed van der Elsken’s archive is comprised entirely of colour slides in plastic support. The Calvin Wells archive is composed of 1450 slides; 96% on plastic supports and 68% are colour. Colour dyes are prone to discolouration and fading due to exposure to light, this is particularly relevant to slide archives as they are likely to have been used multiple times in presentations, lessons, etc.

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Image 5: Examples of discoloured and faded slides from the Calvin Wells Archive

Another interesting point of discussion was about where mould was most commonly found on a slides; whether on the emulsion side or on the support side. The presence of gelatine is greater on the emulsion side however a gelatine layer is also applied to the support side as an anti-curling agent.

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Image 6: ©Graphic Atlas. Cross-section of a colour slide on plastic support

During the practical sessions the participants had the chance to dismantle slides and view them under the microscope to ascertain whether they had mould or not. I was surprised to learn that plasticisers added during the process of manufacturing of the plastic supports can migrate to the surface and form crystals or bubbles.  When viewed under the microscope the pattern of these crystals or bubbles is indeed very different from the pattern of mould.

Left: Mould (white specks) visible with naked eye

Right: Mould spores viewed under the microscope

Left: Plasticiser crystals viewed with naked eye are quite similar to mould spores

Right: Plasticiser crystals viewed under the microscope

Close analysis and visualisation of deterioration is very important in conservation. When slides present a significant amount of mould (as seen in image 7) and the surface is quite rough, the mould spores can become mixed with the dye particles.  In this condition, slides require a further level of treatment which requires them to be isolated and stored in frozen temperatures.

During the workshop, participants had the opportunity to carry out the treatment themselves. After dismantling the slides are slotted into a bespoke polyester sheet, which can accommodate up to 20. The sheets containing the slides are then washed in a combination of water and ethanol, then dried overnight. In the last practical session we had the chance to carry out the treatment on highly deteriorated slides which gave the participants insight into the various risks which can lead to damaging the slides even further.

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Image 11: Slides slotted in the bespoke polyester sheet

Left: During washing

Right: Slides drying

Throughout the workshop Katrin and Lénia provided many useful resources of identification, preservation, care and storage of colour photographic film. There were also plenty of networking opportunities for attendees, which included individuals from Portugal, Spain, Netherlands, Belgium, France, United Kingdom and United States.

I would like to thank the Putting Flesh on the Bones Project and the Wellcome Trust for funding my participation in this workshop. The expertise gained during the workshop will be instrumental in the conservation treatment of the colour slides of the Calvin Wells archive.


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