Two 19th century thangkas from Tibet: examination and conservation by Caroline Ocks

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This study, carried out as a diploma-project, is a multidisciplinary approach to the examination and conservation of two thangkas. The poster version was first presented at the 2015 IIC Hong Kong Congress and it is now published as a full version as part of NiC’s focus on showcasing emerging conservators’ work.

Thangkas are complex objects composed of a central painting sewn into a textile frame, wooden rods at top and bottom with metal knobs as well as a curtain with ribbons. Traditionally they were transported and stored in a rolled state, and therefore also known as painting scrolls.
The thangkas were acquired in the early 1970s in Delhi, India, practically without any knowledge about their origin and dating. Since then, both scroll paintings have developped a high personal value for the owner and consistently accompanied her while travelling around the world, suffering from the handling and constant risks of varying climates.
In 2011 the two painting scrolls reached the Institute of Conservation at the University of Applied Arts Vienna in Austria, being in different state of preservation due both to changing environment, mechanical stress caused by human action and in part to various conservation treatments carried out on the objects at some point in their past.
Art Historical Research
Since the origin of the two thangkas is unknown and their iconography differs in the presentation of composition, but they are framed the same way, two major questions arose: where did they originate? Are the two paintings just framed the same way or part of a bigger ensemble?
Through research and comparison, the thangkas could be attributed to an iconographic programme: Buddha Shakyamuni and the sixteen Great Arhats. This is based on a theme originally printed with block prints in the former printing house of the Nartang monastery in Tibet. The ensemble consists of seven thangkas. In comparing these with block prints from the Tibet House in New Delhi, infrared light analyses have proven that the two thangkas are not completely congruent in execution. No indications of printed under-paint and no colour codes were detected. So, one can only assume that the artists used this block prints as a model. Slight modifications of the motifs are verifying this assumption.

Technical Examination
Along with art historical research, an analytical study of the materials was carried out with optical microscopy of cross-sections and scanning electron microscopy for the pigment compounds, gas chromatography–mass spectrometry (GC-MS) analyses of binding media and composition of organic material as well as imaging with X-radiography and infrared light to clarify the existence of under-paint as well as colour notations.
The result of the analytical research confirmed the use for both thangkas of the same materials: kaolin and magnesium white for the ground as well as other typical pigments in thangka production (e.g. malachite, azurite, gold, vermillion, red lead, etc.).
Since the date of production was unknown, the presentce of chrome yellow (PbCrO4) as well as emerald green was an important discovery to narrow the dating of both thangkas to a period not earlier than 1815-20. Animal glue was used as binding media. In the case of the much later applied consolidant animal glue with traces of dammar was identified.

Condition
Both thangkas suffered from handling and transport damage, and also from previous conservation treatments. The binding media of the paint layer was probably heavily degraded. Therefore a protein-based consolidant had been extensively applied over the painting in a former conservation treatment. It soaked through all layers as well as the painting support and formed a hard and stiff islands of adhesive material on its verso.
Based on these treatments and further oxidation, the support became brittle and stiff. This resulted in multiple tears as well as a hole where the fibres were broken. There were heavy paint losses mostly in combination with the ground layer. Together with to the typical damage caused by rolling of the thangkas, the main reason for the partial losses of the depictions were past attempts at wet surface cleaning (e.g. an indigo coloured sky was almost washed out). The damages are equivalent to the water stains marked on the reverse of the thangkas.

Conservation Treatment
The aim of the conservation treatment was to achieve a similarity in the appearance of both thangkas with minimal intervention. The main focus of the intervention was to secure and stabilise the paintings’ support without losing its function as a scroll painting. Furthermore, a new method for the hanging should be developed to ensure that the main weight of the lower rods would be carried by supporting construction.
After dry surface cleaning with soft brushes and polyurethane sponges the treatment included a reduction of the brittle and stiff protein-based consolidant that had been applied to the painting.
Several methods were tested and a successful reduction was obtained with moist compresses on the suction table. The thick crusts were thinned as far as possible without harming the water-sensitive ground and paint layers.
Deformations of the paintings-support were reduced with moisture and pressure (Gore-Tex®-sandwiches). Tear mending of the support was carried out with a mixture of 20% sturgeon glue and 10% wheat starch paste (ratio 1:2).
An “intarsia” was applied with the same method to close the hole. After the successful stabilisation of the support, in-painting was carried out using dry pigments in 4% Klucel® E in Isopropanol.
Furthermore, a new method for the hanging has been developed to avoid damages through tension and elongation. L-shaped brass-plates were covered with padded Tyvek® to carry the weight of the lower rods without harming the delicate textile-frame.

Acknowledgment:
University of Applied Arts Vienna, Austria, Institute of Conservation: Univ.-Prof. Mag. Dr. Gabriela Krist, Supervisor, Univ.-Ass. Mag. Dr. Natalia Gustavson, Univ.-Ass. Mag. Veronika Loiskandl, Co-Supervisors, VL Dipl. Ing. Tatjana Bayerová, Supervision of analysis, Univ.-Ass. Mag. Agnes Szökrön-Michl, Photo Studio/X-ray/IR; University of Applied Arts Vienna, Austria, Archaeometry Department: AProf. DI Rudolf Erlach, Analysis (SEM-EDX); Conservation Science Department, Kunsthistorische Museum Vienna: Dr. Václav Pitthard Analysis (GC-MS).

References:
1) Shaftel, A. 1993. Intent, In Tents and Intense, 1993, http://cool.conservation-us.org/byauth/shaftel intent.html; Access: 23.11.2012; Lavizzari-Reuber, A. 1984. Thangkas. Rolbilder aus dem Himalaya. Kunst und mystische Bedeutung, Köln, pp. 58.
2) Fiedler, I. & Bayard, M. 1997. Emerald Green and Scheele`s Green. In: E.W. FitzHugh, ed. Artists´ Pigments. A Handbook of Their History and Characteristics 3. National Gallery of Art, Washington & Archetype Publications, London, pp. 219-271; Kühn, H. & Curran, M. 1986. Chrome Yellow and Other Chromate Pigments. In: R.L. Feller, ed. Artists´ Pigments. A Handbook of Their History and Characteristics 1. National Gallery of Art, Washington & Archetype Publications, London, pp. 187-217.

All Images in this article are © Caroline Ocks

Caroline Ocks studied conservation of paintings and polychrome wooden objects at the University of Applied Arts Vienna, Institute for Conservation for five years. After graduating in summer 2013 she worked for the WienMuseum, Vienna as well as a private conservator. She is currently working as an assistant professor at the Institute for Conservation, University of Applied Arts Vienna. Her contact details are: caroline.ocks@uni-ak.ac.at