From stitching silk to X-ray scanning, find out what goes into conserving a sacred object before it goes on display inTantra: enlightenment to revolution.
In summer 2019, a beautiful Tibetan thangka came to the British Museum’s Hirayama studio. It was in poor condition, with light-damaged silk borders and flaking paint, so it needed to be treated by conservators before it could be displayed safely in the upcoming exhibition Tantra: enlightenment to revolution (24 September 2020 – 24 January 2021). During conservation, an exciting prospect arose to also carry out scientific analysis to find out more about this devotional object and its origins.
Thangkas are portable sacred objects with a central painted image, usually painted on a cotton fabric prepared with a ground layer, surrounded by highly decorative silk brocade borders. Wooden rods are attached to the top and bottom to allow for hanging and a silk veil protects the image. Thangkas are traditionally stored rolled and then unrolled for display – this causes damage to the paint layer and textile over time.
This thangka depicts the Mahasiddha Saraha – who you can find out more about in our ‘What is Tantra’ blog. Unusually, this thangka has a stupa (Buddhist shrine) painted on the back and a set of hand prints from when it was consecrated.
As religious objects, thangkas require utmost care and respect during conservation treatment. In the past, original brocade borders were sometimes removed from thangka paintings by art dealers, and in some cases paintings were restored using techniques traditionally used for easel paintings. At the British Museum, we take a holistic approach to treating thangkas and use contemporary conservation techniques from both East Asian Art and textile conservation disciplines.
The first step in the treatment of the thangka was to carefully unpick the stitching that joins the silk brocade border to the painting. The borders were then separated from the painting so the fragile silk could be stabilised. To our delight, this revealed colourful pigment tests in the margins around the painting.
During preliminary examinations of the painting we observed extensive underdrawing in areas where the pigment had been lost. Scientific imaging was carried out to investigate the full underdrawings, as well as to determine the nature of the pigments in the painting and how they related to the pigment tests in the margins. This was a unique opportunity that will not be possible after the textile borders are reattached. Through a combined approach of multispectral imaging (visible, ultraviolet-induced visible luminescence, infrared-reflected, infrared-reflected false-colour) followed by non-invasive analysis it was found that the palette was in-line with traditional thangka painting practices of the 17th and 18th centuries.
The red pigments (red lead and cinnabar) were transparent in the infrared-reflected image, so it was possible to ‘see’ the carbon-based paint underdrawings below the painted surface. In the image below you can see how the folds of the fabric on the left arm of the figure have been changed in the final painting.
Further reworkings were revealed using X-radiography, which uses a source of radiation that penetrates even further beneath the paint layers than infrared light. In the X-ray image below, two sets of gold lines can be seen radiating from the Mahasiddaha Saraha, indicating that the artist chose to cover up the first set of lines with blue azurite pigment and then apply new gold lines in a more upward direction. You can also see the broad brush strokes used to apply the fluid red pigment, as well as the stupa from the back of the painting.
Following scientific analysis, pigment consolidation was carried out to re-adhere any loose or lifting media to the cloth support below. The powdery pigments were stabilised by applying a synthetic cellulose-based adhesive ( Bermocoll® – ethyl hydroxyethyl cellulose) as a fine mist, using an air-brush spray. Under the microscope, a slightly higher concentration of the same adhesive was applied with a tiny brush to adhere loose flakes of paint.
Some areas of the light-damaged textile were splitting and very weak, so these areas were sandwiched between two different support materials – hand-dyed silk crepeline and a fine nylon netting, which were coated in advance with a synthetic heat-set adhesive (Lascaux 498). The crepeline was inserted behind each damaged area and attached to the textile by applying heat with a spatula, and then the fine nylon netting was placed on top of the damaged area and attached in the same way. Some stitching was worked through all three layers to ensure the repairs would withstand future rolling and unrolling of the textile. To complete the treatment, the border and painting were stitched back together.
During treatment it was possible to see the inside of the border, where the dyes used to colour the textile remain as bright as they would have looked originally before extensive fading. Dye analysis revealed that light-sensitive natural dyes, including safflower, indigo, pagoda, sappanwood and probably turmeric, often in combination, were used to create the vivid colour scheme. To ensure that the dyes do not fade further, the thangka will be on display for a limited period of time only, at low light levels (below 50 lux).
All of these elements of close interdisciplinary study and examination were crucial in planning and carrying out an effective treatment of this sacred piece. The work means that the thangka can be enjoyed in all its brilliance when it goes on display as part of Tantra: enlightenment to revolution in Room 35.
We would like to thank Kevin Lovelock (Senior Photographer), Joanne Dyer (Colour Scientist), Daniel O’Flynn (X-ray Imaging Scientist) and Diego Tamburini (Postdoctoral Fellow, Scientific Research) for all of the scientific imaging and analysis carried out during this project.
A full report of the discoveries carried out as a result of scientific analysis will appear in a forthcoming publication.
Find out more about Tantra: enlightenment to revolution and book tickets here.
Supported by the Bagri Foundation