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Conservation varnishes at the National Gallery: Studying their optical and material properties

A fully-funded PhD studentship in partnership with Nottingham Trent University.

Collaborative Doctoral Partnership

The National Gallery offers a small number of Collaborative Doctoral Partnership studentships, funded by the Arts and Humanities Research Council (AHRC) and run in partnership with higher education institutions. These studentships focus on specific themes relevant to the Gallery's collection and wider research themes.

Research project

Drawing on equipment and methodologies developed during a previous collaborative Nottingham Trent University/National Gallery PhD, this project will use non-invasive and portable Optical Coherence Tomography (OCT) and nuclear magnetic resonance (NMR) equipment to take a fresh look at the choice of conservation varnishes, focusing on two aspects. Firstly, OCT and NMR will be used to investigate the effect on a range of varnish properties including saturation, gloss, Tg, etc, of other factors than the choice of resin, e.g. solvent used, formulation (addition of wax, mixing of resins), application method, layering, etc, working with experimental samples and studying the film formation process.

The previous PhD suggested that amongst low molecular weight resins, solvents play as much of a role as the resins in determining the viscosity of a varnish and the final appearance. The project will also explore the wetting behaviour of a varnish with respect to the different paint surfaces as it has always been assumed that all varnish wets the paint surfaces perfectly without any evidence. The OCT equipment permits multi-layer profilometry for simultaneous measurement of the varnish/paint interface and varnish surface smoothness (affecting gloss and saturation).

Secondly, the project will draw on the National Gallery conservation and scientific records and the actual varnishes applied to National Gallery paintings during the 20th century as a unique resource to understand the long term behaviour and properties of naturally aged conservator-applied varnishes. OCT and NMR will allow a (non-subjective) non-invasive assessment of the appearance and current condition (physical, mechanical and some aspects of chemical properties) of the varnishes, providing an opportunity to compare real varnishes based on different resins both to each other, and to the expected behaviour of such varnishes based accelerated ageing, theoretical behaviour of the polymer and the published literature.