As part of Tate's quest to understand the materials and techniques of the paintings of the Pre-Raphaelite Brotherhood, we recently spent some time at CCI with Dr. Leslie Carlyle (Senior Conservator, Materials Historian in the Conservation Processes and Materials Research Division). In 1 week of concentrated work we accomplished a great deal.

The paintings of the Pre-Raphaelite Brotherhood have been a subject of interest for many over the years — at least in part because of the availability of primary source material such as letters and biographies. The startlingly bright colours, the distinctive paint application, the legendary use of zinc white as a ground with paint applied on top wet-in-wet, and the pristine condition of the works are all cited frequently and uncritically in the art historical literature. Tate conservation department is currently in the midst of an extensive research project to examine, record, and interpret the actual materials found in these artists' key works.

One specific material issue is the well-documented use of copal resin both in the paint and as a varnish. Unfortunately, an initial analysis^1,2 of samples taken from a range of works documented as including copal resin failed to confirm its presence. However, refractive index measurements of paint that were made at Tate gave high readings — which clearly suggested that linseed oil was not the only binder and that copal was a material worth investigating in this context.

At this point it was also clear that a better practical understanding of why artists might add copal to paint was needed. This could be achieved by making reconstructions of typical paint layers we had observed on the actual works. But unlike CCI, Tate does not currently³ have the facilities or expertise to produce the oils and copal varnishes needed for this work.⁴ Hence we contacted CCI. It would also be a distinct advantage to use the very materials that were already being analysed and researched as part of Dr. Carlyle's work at CCI.

Our aims were to prepare copal paints using glazing pigments typically found in Tate's Pre-Raphaelite paintings⁵: rose madder, emerald green, cobalt blue, and natural ultramarine. Pigments produced with 'pre-modern' technology were selected from Tate's and CCI's materials archive. Copal resin was added in three ways:

• as a copal oil varnish directly to the dry pigment;
• as dry pigment mulled into linseed oil with copal oil varnish added; and
• as dry pigment mulled into linseed oil with a copal megilp added.

Jacqueline Ridge preparing paint according to recipes such as would have been used by the Pre-Raphaelite painters in England.

Ultramarine blue pigment being ground in oil.

Dr. Joyce Townsend painting out samples of artists' mediums such as those in use at the time of the Pre-Raphaelite painters.

The paints were hand-ground to give a workable glaze colour, and the amounts of pigment, oil, copal varnish, etc. were recorded (this allowed us to work out exactly how much copal was needed in practice to make a useful paint — a point on which documentary sources are frustratingly silent). During the preparation of these reconstructions on carefully selected priming layers we noted the impact that the copal (in its various guises) and diluent made on colour, handling, and drying time. The results were extremely colourful when complete! Once the paint was dry, parts of the boards were varnished with the copal oil varnish.

We generated two sets of reconstructions, one to be kept by CCI and one to travel back to London. The next step in this work will be to record the following information at Tate by means of colour measurements:

• the impact of the different primings beneath the glaze colours;
• the impact of copal addition versus no copal;
• the effect of copal-containing varnish; and
• the refractive index of the various copal formulations.

The boards will then be artificially aged at Tate using a combination of light and heat aging to simulate 150 years, since the Pre-Raphaelites were working in the 1850s. Detectability studies and comparisons of analytical methods for aged copal materials can then be made, in collaboration with Dr. Klaas Jan van den Berg of the Netherlands Institute of Cultural Heritage, Amsterdam (NIC). This in turn will benefit other institutions attempting to analyse these rather intractable materials.

This approach to materials research allows us to combine the expertise of Dr. Leslie Carlyle in materials history, the technical evidence from Tate's significant collection of Pre-Raphaelite paintings, and the scientific resources of the NIC. The results, when published in 2003–2004, will be of use to conservators, conservation scientists, and art historians alike, and will also be made available to the wider public through books and lectures.

1. van den Berg, K.J., J. van der Horst, and J.J. Boon. "Recognition of Copals in Aged Resin/Oil Paint and Varnishes." pp. 855–861 in ICOM Committee for Conservation 12th Triennial Meeting Lyon 29 August – 3 September 1999: Preprints Volume 2. London: James & James (Science Publishers) Ltd., 1999.
2. Hackney, S., J. Ridge, J.H. Townsend, K.J. van den Berg, and L. Carlyle. "Visual Deterioration in Pre-Raphaelite Paintings." pp. 57–59 in Deterioration of Artists' Paints: Effects and Analysis (a joint meeting of the working groups Paintings 1 and Paintings 2 of the International Council of Museums - Committee for Conservation and the Paintings Section of the United Kingdom Institute for Conservation) (edited by A. Phenix). London: British Museum, 2001.
3. Tate is completing its design brief for a new Collections Centre. The visit to CCI gave us a welcome opportunity to observe another building of comparable size and function.
4. Carlyle, L., N.E. Binnie, G. van der Doelen, J. Boon, B. McLean, and A. Ruggles. "Traditional Painting Varnishes Project: Preliminary Report on Natural and Artificial Aging and a Note on the Preparation of Cross-sections." pp. 110–127 in Varnish: Material - Aesthetics - History: International Colloquium, Braunschweig, 15–17 June 1998. Braunschweig, Germany: Herzog Anton Ulrich-Museum, 1999.
5. Hackney, S., R. Jones, and J. Townsend. Paint and Purpose: A Study of Technique in British Art. London, UK: Tate Publishing, 1999, pp. 74–85.