Strategies for the preservation of a b/w motion picture film collection in safety film support

This thesis aims to contribute for reviewing Safety film preservation guidelines currently in practice, concerning film identification, film assessment and storage conditions in the archive, Arquivo Nacional das Imagens em Movimento (ANIM – National Archive of Moving Images), conservation center of Cinemateca Portuguesa. Since the 1980s, stability issues and degradation factors concerning the oldest type of safety film, cellulose triacetate (CTA), have been studied. Based on the results accomplished with those studies, preservation guidelines were established highlighting the advantages of low temperature and low relative humidity for film stability. Despite the guideline’s disclosure, there are practical issues, such as lack of staff, financial restraints and lack of studies regarding polyethylene terephthalate (PET) films decay, that ultimately jeopardize the preservation of motion film collections. In order to have an overall comprehension of the identification and assessment methods used, a review of relevant literature about national and international guidelines for film preservation was performed. This review endowed a broader understanding of the identification, assessment and monitorization carried out in ANIM archive. Aiming to understand preservation practices, an investigation was undertaken at ANIM. Current identification and assessment methods were reexamined, tested and reevaluated. Based on the results accomplished, new identification and assessment tools, as well as, recommendations concerning organization and storage are proposed. For the experimental part of this work, identification and assessment of film (image and sound) were performed. For this internship and study, it was decided firstly to perform the identification and assessment of 100 films and film cans according to the macro identification and macro assessment methods described in the literature. For macro assessment, Acid Detection (A-D) strips and macro signs of degradation were used to evaluate the condition of the films studied. Moreover, the macro assessment results obtained in 2006 and 2014 were also analyzed. In order to identify possible degradation trends and contribute to the review of the current preservation practice, past and present macro assessment results were compared. Additionally, new assessment methods, such as hardness measurement, hardness (Shore A), were tested. The results obtained confirmed that free acidity tests are effective methods for monitoring safety film decay. In this study it was also possible to identify degradation trends, specifically concerning magnetic tapes. Moreover, besides CTA film decay, during the macro assessment of ANIM’s collection, PET films degraded were found. Based on these results it was possible to propose a new methodology for film preservation

Beyond linear elasticity: Jammed solids at finite shear strain and rate

The shear response of soft solids can be modeled with linear elasticity, provided the forcing is slow and weak. Both of these approximations must break down when the material loses rigidity, such as in foams and emulsions at their (un)jamming point -- suggesting that the window of linear elastic response near jamming is exceedingly narrow. Yet precisely when and how this breakdown occurs remains unclear. To answer these questions, we perform computer simulations of stress relaxation and shear startup experiments in athermal soft sphere packings, the canonical model for jamming. By systematically varying the strain amplitude, strain rate, distance to jamming, and system size, we identify characteristic strain and time scales that quantify how and when the window of linear elasticity closes, and relate these scales to changes in the microscopic contact network. Our findings indicate that the mechanical response of jammed solids are generically nonlinear and rate-dependent on experimentally accessible strain and time scales.Comment: 10 pages, 9 figure