Alan Phenix

Application of chemical and thermal analysis methods for studying cellulose ester plastics.

Cellulose acetate, developed about 100 years ago as a versatile, semisynthetic plastic material, is used in a variety of applications and is perhaps best known as the basis of photographic film stock. Objects made wholly or partly from cellulose acetate are an important part of modern and contemporary cultural heritage, particularly in museum collections. Given the potential instability of the material, however, it is imperative to understand the aging mechanisms and deterioration pathways of cellulose ester plastics to mitigate decomposition and formulate guidelines for storage, exhibition, and conservation. One important aspect of this process is the ability to fully characterize the plastic, because variations in composition affect its aging properties and ultimate stability. In this Account, we assess the potential of a range of analytical techniques for plastics made from cellulose acetate, cellulose propionate, and cellulose butyrate. Comprehensive characterization of cellulose ester plastics is best achieved by applying several complementary analytical techniques. Fourier-transform IR (FTIR) and Raman spectroscopy provide rapid means for basic characterization of plastic objects, which can be useful for quick, noninvasive screening of museum collections with portable instruments. Pyrolysis GC/MS is capable of differentiating the main types of cellulose ester polymers but also permits a richly detailed compositional analysis of additives. Thermal analysis techniques provide a wealth of compositional information and thermal behavior. Thermogravimetry (TG) allows for quantitative analysis of thermally stable volatile additives, and weight-difference curves offer a novel means for assessing oxidative stability. The mechanical response to temperature, such as the glass transition, can be measured with dynamic mechanical analysis (DMA), but results from other thermal analysis techniques such as TG, differential scanning calorimetry (DSC), and dynamic load thermomechanical analysis (DLTMA) are often required to more accurately interpret the results. The analytical results from this study form the basis for in-depth studies of works of art fabricated from cellulose acetate. These objects, which are particularly at risk when stored in tightly sealed containers (as is often the case with photographic film), warrant particular attention for conservation given their susceptibility toward sudden onset of deterioration.

The Swelling of Artists' Paints in Organic Solvents. Part 2, Comparative Swelling Powers of Selected Organic Solvents and Solvent Mixtures

Abstract This article describes the swelling responses of two oil paint films as a consequence of immersion in solvents of various kinds. The two test paint films have the same original formulation and are based on proprietary artists oil colors containing yellow ocher and flake white pigment bound in linseed oil: one was aged by exposure to high light dosage, and the other was unexposed. Lateral, inplane swelling of the paint films during immersion in solvent was determined by a simple microscopical method using computer-based image analysis. Results are reported for the swelling of both paint films in more than 55 common solvents and 14 binary solvent mixtures containing ethanol. Data are presented as swelling curves of percentage change in area as a function of time and as plots of degree of maximal swelling as a function of selected solvency indicators. The results are discussed in comparison with existing data on the swelling of oil films by organic solvents and in relation to the implications for the cleaning of oil-based paints.

The Swelling of Artists' Paints in Organic Solvents. Part 1, a Simple Method for Measuring the In-Plane Swelling of Unsupported Paint Films

Abstract A simple method is presented for measuring the in-plane swelling of paint films when immersed in solvents. The method is a development of a low-power microscopy approach first described in the 1960s, with improvements to the measurement aspect through the use of computer-based digital image analysis. Small fragments of paint (2–5 mm2) from stock films of uniform thickness are immersed in the test solvent, and images of the samples are captured electronically at intervals from t = 0 until equilibrium swelling is reached. Image analysis software is used to measure change in the areas of the fragments over time, resulting in swelling curves of time vs. % change in area. The experimental method is described in detail, together with a discussion of key factors relevant to uncertainty in the results. The swelling behavior of various paint films in ethanol and in some other common solvents is described.

Mineral Spirits-Based Microemulsions: A Novel Cleaning System for Painted Surfaces

This paper reports further developments emerging from a collaboration between The Dow Chemical Company, Tate, and the Getty Conservation Institute which seeks to explore improved cleaning systems for unvarnished modern painted surfaces. Specifically, the present study describes three novel microemulsion systems based on water and mineral spirits, each formulated with different surfactants, either ionic or non-ionic. Of particular interest in the systems examined is their capacity to form thermodynamically stable water-in-oil (solvent-continuous) microemulsions which are clear, fluid, and simple to prepare. Phase diagrams are presented for each system type. Compared against more conventional aqueous and hydrocarbon solvent cleaning liquids, findings are reported of systematic evaluations of the performance of selected microemulsion formulations in cleaning artificially soiled reference paint films. Summaries are included of case study conservation treatments conducted at Tate in which the mineral spirits-based microemulsions formed part of the surface-cleaning treatment strategy.

Examination of the wall paintings in Tutankhamen's Tomb: Inconsistencies in original technology

Abstract The collaboration between Egypts Supreme Council of Antiquities (SCA) and the Getty Conservation Institute (GCI) to conserve the tomb of Tutankhamen in the Valley of the Kings provided an opportunity for in-depth investigation of the techniques and original materials of the burial chamber wall paintings. Examination through visual observations, in situ microscopy and ex situ analysis of samples identified discrepancies in setting-out and preliminary procedures and variance in planning and execution from wall to wall. These incongruities can be explained by workshop practice and other constraints, not uncommon in ancient Egyptian tomb execution. However, they additionally support the premise that the early death of the young Pharaoh, and the subsequent adaptation of a pre-existing tomb, had a significant impact on its construction and decoration. Moreover, it is possible that these unique circumstances contributed to particular forms of deterioration, most notably the extensive presence of brown spots on the painting scheme. Reassessing the technical history of the tomb is therefore an essential first step in formulating appropriate approaches to its current conservation.

Curling, ripples, dimples: Observations from a condition survey of animation cels

Animation cels Many animated films of the twentieth century were created using the method based on hand-painted animation cels. Cels are transparent sheets of cellulose nitrate, cellulose acetate, or polyester that are inked and painted by hand with characters reproduced from drawings created by animators. Sequences of animation cels photographed on motion picture film and played back at 24 frames/ second give the illusion of motion. At the functional level, cels were not required to physically survive beyond the duration of the film production. Many cels were ‘recycled’ by washing off the ink and paint in order to reuse the plastic sheets. Others were discarded or sold in limited quantities. Nowadays the remaining cels represent important physical evidence in the history of cinema. Animation cels today are no longer considered as simple functional items created solely for the purpose of making a movie, nor just as valuable collectibles, but also as works of art in their own right. They serve as historical as well as technological and cultural documents of their time. Unfortunately, over time cellulose nitrate and acetate have proved to be highly vulnerable to deterioration via hydrolysis. Eventually, this led to wrinkles and discoloration of the plastic sheets, and related mechanical damage of paint layers, which are manifested distinctly in cels today. Little research has been carried out with a specific focus on remedial and preventive conservation of animation cels. Some of the approaches to film preservation can be applied where the preservation of the cellulose acetate support is concerned (Reilly, 1993; Nishimura, 2015). However, these approaches do not address the particular challenges resulting from the combination of plastic sheet and applied paints. Animation cels at the Walt Disney Animation Research Library Many of the best known animated films of the twentieth century, such as Snow White and the Seven Dwarfs, The Jungle Book, and The Little Mermaid, were created at the Walt Disney Animation Studios. Approximately 500,000 animation cels are stored in the Walt Disney Animation Research Library (ARL) collection. Cels at the ARL are stored within climate-controlled storage vaults (47% RH, 16.6°C) in archival quality cardboard boxes arranged horizontally on movable compact shelving. The inner housing is subdivided into stacks according to their scene in a sequence, meaning that most sheets within a stack have characters in almost the same position. Each cel stack is sandwiched between cardboard. Usually, individual cels are separated by a sheet of paper or polyethylene. An average of 150 cels are stored in one box, with an average of 10 cels within each stack.

A productive collaboration between conservation and industry: Developing wet surface cleaning systems for unvarnished painted surfaces

The poster describes in outline the iterative process and some of the achievements of a collaboration, established in 2008, between Tate, the Getty Conservation Institute (GCI) and the Dow Chemical Company which aimed to develop and test novel wet (liquid) surface cleaning systems for unvarnished painted works of art. This research theme developed from discussions among the group about pressing scientific challenges relating to the conservation of modern and contemporary art. For reasons connected with the lack, at that time, of low-risk, effective cleaning systems for acrylic paintings and the emerging body of scientific research into the properties of acrylic paints (including ageing and the effects of common cleaning treatments), the Tate/GCI/Dow group chose to focus on cleaning systems for works of art made with acrylic dispersion (latex; emulsion) paint media. Initial research considerations were wide in scope, including issues such as: establishing a wider context for the research; exploring potential impact; requirements for internal and external communication; negotiating non-disclosure agreements; establishing a common technical language; defining the requirements for conservation materials; and how to create test materials (type, curing and ageing of paint substrates, artificial dirt, etc.) that are reasonably representative of the real thing. As the initial studies involved the use of Dow’s high throughput technologies (HTP) as a screening tool to assess dirt removal efficacy of different cleaning systems (Fig. 1), discussions also considered how best to approximate some of the physical aspects of cleaning treatments, such as swab rolling action and pressure. A robotic cleaning device was created at Dow that was able to compare, in a time-efficient manner, the cleaning efficacies of a large number of different cleaning formulations. The preliminary HTP cleaning efficacy trials compared the performance of some existing conservation cleaning preparations, both water-based and hydrocarbon solvent-based, with formulations and surfactants that were not familiar to the conservation field (Keefe et al., 2011; Ormsby et al., 2013). Outcomes from the HTP cleaning trials included the identification of a group of useful non-ionic, non-APE, surfactants (products from the Dow ECOSURFTM surfactant range), and a recognition of the possibilities of tailoring water-in-oil (WiO) microemulsions to the application of cleaning acrylic paint. The preliminary HTP cleaning efficacy trials created a large amount of data; ancillary outcomes included HTP systems for quantifying, processing, and interpreting large datasets of comparative cleaning efficacy results. At this point, several new surfactants (ECOSURFTM EH-3, EH-6, and EH-9) and four series of predominantly water-in-oil microemulsion wet cleaning systems (Fig. 2) have been designed through an iterative process, evaluated, and introduced to the conservation profession (Ormsby, Keefe et al., 2016). After development, the next stage involved: the evaluation of potential cleaning systems at Tate, largely through the efforts of a series of interns (both scientists and conservators); the use of systems on case study works of art where appropriate; the introduction to, and evaluation of systems at continuous professional development CAPS (Cleaning Acrylic Painted Surfaces) workshops hosted by the GCI, which have thus far been delivered in the USA, UK, Canada, and Australia; and the publication of information on a regular basis, predominantly in conservation literature. Each stage in the process has necessarily involved all of these aspects, in addition to periods of reflection and re-evaluation of Correspondence to: Bronwyn Ormsby, Conservation Department, Tate Britain, Millbank, London SW1P 4RG, UK. Email: bronwyn.ormsby@tate.org.uk