Tag Archives: featured

Monument Monitor at Home – send us your old photos to help preserve historic sites

The Monument Monitor project, led by SEAHA student Rosie Brigham, has been making headlines recently by asking members of the public to look through their old holiday snaps. Monument Monitor aims to assess how we can best use visitors’ photographs to assist with heritage management. At 20 different case study sites in Scotland, Rosie and project partner Historic Environment Scotland are using visitors’ photographs to assess whether they can monitor all manners of agents of change. Photographs can help with many types of conservation, from levels of Damp in Tarves Tomb, to erosion at Ness of Burgi and biological growth at Neolithic rock art sites around the south west. While visiting heritage sites is no longer possible for most of us, people have still been helping contribute to real scientific research by dusting off old photo albums and sending in their holiday snaps.

At Machrie Moor Stone Circles, for example, Rosie is attempting to model the frequency of severe waterlogging around the site. The standing circles situated on the Isle of Arran are one of the islands most picturesque monuments and comprises of 6 stone circles of various sizes. Parts of the site are frequently waterlogged, and Rosie has been mapping the regularity of this in the submitted images. Using machine learning to identify levels of flooding alongside historic weather data means that Rosie and her project partners are now building up a good idea of the conditions that lead to severe flooding. This is helping us understand how the site is coping with the changing climate of Scotland.

Further north in Inverness, Yuni Chen is working on using photographs submitted of Clava Cairns to establish was has been dubbed as the ‘Outlander Effect’. Since the broadcasting the popular period drama Outlander on Amazon Prime, the site has become a must see on tours of the highlands as it inspired Craigh Na Dun, the time traveling stones at the centre of the drama. Since 2014 there has been a huge increase of visitor numbers at the site, but as it is unstaffed, it is difficult to assess what potential issues this may be having. Using photos taken both before and after the dramas release, Yuni is measuring the erosion to see how much the increased visitor numbers has eroded the ground around the cairn entrances.

To map conservation, Rosie and Yuni are using photogrammetry to produce a 3D point cloud from overlapping images taken from different perspectives. Taken together, these can help to create accurate measurements of eroded areas. Alongside this, the team are using known measurements (such as the width of the stones at the cairn entrances) to calculate the ratio of pixels in areas of interest allowing us to measure scale of the erosion over time.

Rosie’s project has been featured in the The Arran Banner, The Scotsman, The Times, The Press and Journal, and The Sunday Post as well as being featured on the Historic Environment Scotland blog.

Find out more about Monument Monitor, and submit your photos to submissions@monumentmonitor.co.uk

Rosie Brigham is a SEAHA PhD student based at the Institute for Sustainable Heritage at University College London. Her research, partnered with Historic Environment Scotland, Rekrei, and Instadeep, explores how crowdsourced images can be used for conservation monitoring. 

Guest lecture ‘Managing Heritage Landscapes: Past, Present and Future’ at University of Oxford

The SEAHA Landscape Heritage Study Group and Oxford University Heritage Network are pleased to announce their joint guest lecture ‘Managing Heritage Landscapes: Past, Present and Future’ by Dr Tom Tew.

About Tom Tew

After his PhD at Oxford’s Zoology Department, nature conservationist Dr Tom Tew spent over 20 years in the public sector, leading teams and programmes at local, regional, national and international levels. He was a regional and national director at English Nature, and Chief Scientist at Natural England. Tom is currently Chief Executive of two companies that work with planning authorities, landowners and developers to help the planning system deliver net gains for wildlife. He was the Chairman of The Vincent Wildlife Trust and is currently a Trustee and main Board member of both the National Lottery Heritage Fund and The National Trust.

The event will be held on 5 February 2020, at St Cross College, University of Oxford.

Register for the event here.

For more information, please contact head of the SEAHA Landscape Group, Sam Woor.

SEAHA student Ida Ahmad publishes research modelling the degradation of archival films

SEAHA student Ida Ahmad has recently published her research “Are we overestimating the permanence of cellulose triacetate cinematographic films? A mathematical model for the vinegar syndrome” in Elsevier journal Polymer Degradation and Stability.

Cellulose triacetate (CTA) films replaced cellulose nitrate films around the mid-20th century due to the flammability of cellulose nitrate. For this reason, CTA films were also known as “safety film”. However, CTA films were susceptible to other types of damage.

It was first observed that CTA films stored in warmer environments after some time started to emit a vinegar-like odour. Thereafter, the afflicted films began to show other signs of damage such as embrittlement, shrinkage, channelling and the appearance of crystals or bubbles on the surface. CTA films often appeared stable for long periods of time, before the initiation of what came to be known as the “vinegar syndrome.”

The vinegar odour is caused by the emission of acetic acid from the CTA base of the film, which is produced when moisture reacts with the CTA molecule. The progress of this reaction can be measured by the free acidity of the film, defined as the millilitres of 0.1 M sodium hydroxide required to neutralise 1 gram of film base. Film conservation guidelines recommend that a free acidity of 0.5 is considered the point at which the vinegar syndrome starts. After this point, the reaction rate appears to increase markedly, along with other visible signs of degradation.

The reason that the reaction rate accelerates is because acetic acid catalyses the reaction which produces it. This is known as autocatalysis. It is believed that the acid is also responsible for catalysing processes which result in further symptoms of degradation. Heat and moisture promote this reaction, as well as poor ventilation, as this prevents acetic acid from offgasing and so enhances the effect of autocatalysis.

Previous research has attempted to predict the time until onset of the vinegar syndrome, or permanence, of CTA films as a function of temperature and relative humidity. These models assume that all the acid is retained in the film, but they do not account for autocatalysis, as it was believed that the effect of this was not important before the onset of the vinegar syndrome.

Ida developed a mathematical model which accounts for autocatalysis at all levels of acidity. The kinetic parameters for the model were obtained by fitting to published experimental data of artificial ageing of CTA film. The model predictions were validated against a different set of published experimental data at lower temperature conditions. A good agreement was found between the predictions and the data.

Using the model, Ida made predictions for film permanence at a range of temperatures and relative humidity typically found in archives. These were compared against the predicted film permanence according the film conservation guidelines, which do not account for autocatalysis prior to the onset of the vinegar syndrome. This showed that the guidelines may be overestimating the permanence of CTA films. Significantly, based on the age of most CTA films, the model predicts that there are film collections today or very soon which are at risk of developing the vinegar syndrome much sooner than may be anticipated by conservators if they are following the guidelines.

Read the article here.

Header image: Cellulose triacetate 16 mm film, dated 1968, showing advanced stages of vinegar syndrome. Credit: Ida Ahmad.

Ida Ahmad is a SEAHA PhD student based at the Institute for Sustainable Heritage at University College London. Her research, partnered with Tate and Process Systems Enterprise, uses mathematical models to predict how plastic artefacts in museum collections degrade over time.