Eight million photographs: how can science help? – Jacquie Moon, the National Archives

As part of British Science Week 2017 the National Heritage Science Forum is featuring blog posts from heritage scientists from across its member organisations. This year’s theme is ‘sharing heritage science’, and the blogs over the rest of the week will give an insight into the many different forms that heritage science can takes, as well as some of the different ways of getting involved.

Jacqueline Moon is the Senior Conservator for Public and Academic Engagement at the National Archives. She specialises in the conservation of photographs. In this blog, Jacqueline describes how she is using science to care for the photographic collection with the help of volunteers.

The National Archives’ collection includes approximately eight million photographs. The subjects are varied, and include Victorian and Edwardian photographs from the 1850s; of Eccles cakes, circus performers with boa constrictors, ‘the oldest lady in bed’, children acting out barber shop scenes and the Titanic. Later collections include the more serious Operation Sandstone, a unique survey of the British coastline which began in 1947 to help NATO forces plan a re-invasion in case the country was taken over by communist forces.

Their sensitivity to moisture and pollutants poses unique challenges for preservation and conservation. To understand these collections better, the Collection Care department at The National Archives’ is doing a survey with the help of volunteers, who have been trained to identify photographs and understand their deterioration. Their observations are helping us prioritise conservation projects, improve storage and use science to build a more accurate picture of the collection. Without their help it would be impossible.

15b_TNA_Figure 1. Cross section of SG photo - JM.jpg
A cross-section of a silver gelatine photograph on fibre-based paper

Silver gelatine photographs are prone to mirroring (a bluish reflective sheen seen in the shadow areas), yellowing and fading. This is because of changes to the image silver which can be caused by high relative humidity, pollutants or poor processing. Experts claim to be able to look at a deteriorated photograph and tell the causes; an image affected by high humidity would have a more yellowed appearance but an image which has been poorly processed would look more orange brown.  

Top: A well processed test photograph partially aged and the same photograph at x150,000. Below: A poorly processed test photograph partially aged and the same photograph at x150,000.

The photograph conservator at The National Archives undertook research into the deterioration of silver gelatine photographs, the commonest type in the collection, to find out if a simple colour measurement by non specialists could help make conservation decisions, such as prioritising certain items for cool storage and selecting others for the exhibitions and the loans programme. A number of scientific techniques were used to study a set of laboratory made and historical photographs. The techniques included spectrophotometry (a method for quantifying colour), transmission electron microscopy (effectively a microscope but instead of light and lenses it has electrons and electromagnetic fields) and spot tests to test for impurities 

15b_TNA_Figure 3. Taking colour measurements of yellowed historical photographs - JM.JPG
Taking colour measurements of a series of sample photographs

The colour measurements showed that photographs affected by poor processing had red and purple hues, whilst transmission electron microscopy showed they had clumped image silver; those affected by high relative humidity were more yellow but had lots of spherical silver particles, called colloidal silver (see image 2)

The next steps are to prove this on a larger scale so it could be used more widely; testing records affected by yellowing using information gathered during the survey. Volunteers will be trained to collect and interpret the colour data and the results will be publicised in due course. If you’d like to read more about how we care for the photographic collection at The National Archives, you can read our blog here.

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