Category Archives: SEAHA student publication

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. 

Fabiana Portoni publishes paper on the application of a technique to measure pesticide residues in contaminated museum artefacts

SEAHA aligned student Fabiana Portoni, alongside her supervisors Professor Matija Strlič and Dr Josep Grau-Bové, has recently published an article in the journal Heritage Science from Spinger Nature. The paper entitled “Application of a non-invasive, non-destructive technique to quantify naphthalene emission rates from museum objects” focuses on the development of an application to measure volatile pesticides residues in museum objects.

Insect pests can cause damage to museum collections. With the aim to protect objects from pest damage, it was once common in museums to use a wide range of pesticides. This was commonly practiced until as recently as the 1990’s. Nowadays, most museums steer away from using toxic chemicals on the objects. However, contamination from earlier treatments can still be a concern for people working with and accessing the collections.

In the last 30 years, the cultural heritage field has undertaken research to identify which pesticide residues remain in their collections and increase their knowledge regarding levels of contaminants present. Therefore, obtaining confirmed quantities of volatile organic residues, and their impact on the air quality surrounding objects, has been identified as an area that would benefit from further investigation.

Fabiana’s study analysed a group of organic objects from the British Museum collection with suspected contamination. After an initial screening to identify the pesticide compounds present in the objects, naphthalene was identified as the most common residue present. Therefore, it was decided to focus the research on this specific compound.

To ensure the long-term preservation of museum objects, it is preferable not to damage them by removing physical samples. The sampling methodology proposed in this study complied with this preference. In addition, the method proposed could be undertaken in situ at museum or heritage sites without impacting on the surrounding environment.

So what was the method? The technique required the object to be placed inside a sampling chamber. This chamber was fitted with an air pump. Air forced through the chamber by the air pump then passed through sorbent tubes. Volatiles emitted by the object could be collected into the sorbent tubes. Later analysis allowed identification of the volatiles and their concentrations.

The results for this research showed the concentration of naphthalene being emitted into the air over a period of time. Calculation of active emissions from individual objects is useful in understanding the behaviour of said objects and their impact on air quality in common museums situations. The information obtained was used to model the naphthalene concentrations for a period of time inside 3 common museum scenarios: a box, a display case and a storage room. The aim of gathering these results is to inform ventilation strategies and improve the dissipation of residues.

The paper states it would be interesting to use the method presented to asses a larger percentage of museum objects and get a relevant sample size of the collection.

To learn more about the project read the open access paper here!

 


Fabiana Portoni graduated from the MRes in Heritage Science at UCL Institute of Sustainable Heritage. She currently works as a Preventive Conservator for the British Museum.

Jenny Richards publishes research investigating the deterioration of earthen heritage by wind and rain

Oxford-based SEAHA student Jennifer Richards has recently published her research ‘a controlled field experiment to investigate the deterioration of earthen heritage by wind and rain’ in Springer Heritage Science.

Earthen heritage is one of the oldest and most universal forms of heritage with sites dating back to the Neolithic and being found of every continent. Earthen sites also make up 10% of the World Heritage List but are over represented on the World Heritage in Danger list in part due to the extensive deterioration occurring at the sites which threatens to reduce their value.

Deterioration of earthen heritage is affected both by material properties and environmental conditions. However, as conservation strategies try to limit the extent to which historic material is altered, more research is needed to understand how environmental conditions cause deterioration.

Wind driven rain, wind and sediment laden wind (wind which is transporting sediment) all drive the deterioration of earthen heritage with rain noted as causing the greatest rate of deterioration over short periods.

This study utilised a unique opportunity to undertake deterioration experiments at the remote and under-studied site of Suoyang Ancient City, Gansu Province, China. This study (i) compared effect of wind, sediment-laden wind and wind-driven rain in causing deterioration to earthen heritage and (ii) how the incipient deterioration features produced by wind, sediment-laden wind and wind-driven rain on the test wall relate to the deterioration features recorded on the historic city walls.

This research used a test wall built out of rammed earth to the East of the historic walls at Suoyang. The test wall was subjected the wall to low, medium and high intensities of wind, sediment laden wind and rain and laser scanning was used to assess the extent of the deterioration caused by each test run.

The deterioration features caused by each environmental force were notably different and could be mapped onto the historic walls. Clean wind caused the least deterioration and only removed loose material from protruding areas of the wall, while sediment-laden wind caused pitting (small concave features in the wall surface). Wind-driven rain caused the greatest deterioration with the formation of incipient gullies down the wall face. However, the low frequency of rainfall at Suoyang is likely to limit the extent to which rainfall can cause deterioration at the site, whereas the almost continual nature of erosive wind events suggests that wind may play an important role in causing deterioration even though it only has a low magnitude impact.

Further research is needed to understand how climate change will affect the environmental forces operating at Suoyang as increases in the frequency of rainfall or the speed of the wind could result in faster rates of earthen heritage deterioration. These findings show that conservation strategies at earthen sites like Suoyang need to address the impact of multiple environmental forces, such as clean wind, sediment laden wind and wind-driven rain.

Read the article here!


Header image: Jenny and her field work. Credit: Dunhuang Academy

Jenny Richards is a SEAHA DPhil student based at the School of Geography and the Environment at the University of Oxford. Her research, partnered with The Getty and Dunhuang Academy, evaluates site-based conservation approaches to mitigating climatic risks to earthen heritage sites in N W China.  

SEAHA student publishes research on multiple identities from burial evidence in the Beaker period

SEAHA student Richard Higham (UCL/University of Brighton) has recently published two papers on his research investigating variation in grave assemblages and the construction of social identity during the Beaker period (2450BC- 1650BC). Working alongside his supervisor Dr Chris Carey (University of Brighton), Richard analysed collections and archives of Beaker burials from Devizes museum, Keiller museum, Chichester museum and the Ashmolean museum, in order to identify variation in burial practice during the Beaker period.

The research is part of a wider analysis of variation into Beaker period funerary practices and began with reanalysing the grave goods from the Durrington Sarsen Burial (see image). The grave goods of this burial indicates a burial date of 2250-1950BC, a time when Beaker burials dominate the archaeological record. The location of this curious burial, which had been excavated in 1809, was lost to archaeology.   However, by investigating past maps and letters, the probable location of this burial was identified, just outside the bank of the Durrington walls henge. The absence of the Beaker pottery vessel is interpreted as significant, given that the burial is located within the Stonehenge monumental landscape, which contains numerous Beaker burials containing a range of prestige grave goods.

This research lead to a reconsideration of the archaeological narrative of the Beaker period, which has been dominated by the study of Beaker pottery and the ‘Beaker people’. Examples were found of Beaker period burials that excluded Beaker pottery from the grave assemblage.  This reasearch considered what these burials represented in terms of social identity and whether they can be interpreted as Beaker burials or represent other identities co-existing alongside Beaker societies. The publication aims to highlight the variation within the burial practices of the Beaker period and promote discussion of multiple identities during this dynamic period of prehistory.

Read the two papers below:

Higham, R., & Carey, C. (2019). The Durrington Walls Sarsen Burial relocated and reconsidered. Wiltshire Archaeological and Natural History Society, 112, 74-84.

Chris Carey & Richard Higham (2019) Multiple identities in the Beaker period: interpreting inhumations out of the Beaker spotlight in southern England, Archaeological Journal


Richard Higham is a SEAHA student in his MRes year currently based at the Institute of Sustainable Heritage at the University College London and will go on to study his PhD at School of Environment and Technology at the University of Brighton. Supported by Historic England and Trent and Peak Archaeology, his present research is ‘Evaluating evaluation trenching in archaeological projects’.

Header image: The original engraving of the finds from the Sarsen Burial published in Ancient Wiltshire (1812), drawn by Phillip Crocker, with annotation. These finds are now on display in Devizes Museum.

SEAHA and ISH research on epidemiology for heritage collections published in Heritage Science journal

Former Institute for Sustainable Heritage (ISH) student, presently SEAHA student Cristina Duran-Casablancas has recently published a series of papers on wear and tear in archival and library collections in the journal Heritage Science, with her supervisors Dr. Josep Grau-Bové, Prof. Tom Fearn and Prof. Matija Strlič.

An intrinsic value of archival collections is that they are physically used, which undoubtedly leads to a certain level of wear and tear. This reasearch explores whether differences in individual items might explain patterns of decay across a population, as well as how reliable different groups of objects are.

In ‘Accumulation of wear and tear in archival and library collections. Part I: exploring the concepts of realibility and epidemiology’ the authors explore how realibility theory, the method that deals with failure in complex systems, and epidemiology, which explores deseases in defined populations, could be applied in the heritage field to provide quantitative evidence of patterns of decay on large heritage collections.

Part II of the study, ‘Accumulation of wear and tear in archival and library collections. Part II: a epidemiological study’, proposes a new methodology to collection surveying based on epidemiology. The results show that appropriate survey methods and statistical methods of data analysis can reveal the factors that can lead to wear and tear.

Read the two papers below:

  1. ‘Accumulation of wear and tear in archival and library collections. Part I: exploring the concepts of reliability and epidemiology’
  2. ‘Accumulation of wear and tear in archival and library collections. Part II: a epidemiological study’

This article is part of the SEAHA CDT collection in the journal Heritage Science.

SEAHA student Cristina Duran presenting research on epidemiology for heritage collections at the 18th ICOM-CC Triennial Conference, September 2017, Copenhagen. Read the paper presented at the conference ‘Data mining in collections: from epidemiology to demography’ here.

 


Cristina Duran-Casablancas is a SEAHA student based at the Institute of Sustainable Heritage at the University College London. Supported by National Archief (NL) and Helicon Conservation Support, her present research explores the use of System Dynamics and related mathematical modelling techniques to evaluate the effect of preservation actions during the lifetime of collections.

Header Image: Repositories at the Amsterdam City Archives (© Stadsarchief Amsterdam).