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TECHNICAL RESEARCH (Continued)
SYNOPSIS OF SCIENTIFIC ANALYSIS
Tondo - Madonna and Child
McCrone Research Associates Ltd, London NW3 5BG
Shirley Institute, Didsbury, Manchester M20 8RX
UK Forensic Science Services Ltd, Melbourn, Royston, Herts SG8 6EJ
Cambridge Environmental Research Consultants Ltd, Cambridge CB3 0AX
[Department of Earth Sciences, Cambridge University]
Clare Meredith, Conservation Studio, West Lothian EH30 9SL
Henry Bland, Consulting Forensic Scientist, Foxton, Cambridge CB2 6SR
Dr Jan Wouters, Director, Laboratory for Materials and Techniques, Royal Institute for Cultural Heritage, Brussels
Professor Howell Edwards, Professor of Molecular Spectroscopy, University of Bradford
The support is of flax with a faint red earth colouring. It is a tight, plain, tabby weave of very good quality. Although thin and tightly woven, the threads are uneven suggesting that the flax has been hand-spun and hand-woven. The canvas, although brittle at the edges, appears to be in good condition. It is not lined. On visual examination, the dark tone of the fibres suggests that they have been saturated with wax. Chemical analysis reveals that they have been impregnated with a fossil-type resin, possibly amber, or impregnated and coated with wax and resin. There is no evidence of gelatin or animal glue on the fabric. [Report of Clare Meredith dated 24 January 1989].
Paint Analysis - Examination Techniques:
Low Power Stereo Microscope
Examination of paint samples by this method and comparison against reference slides identified the following pigments:- red madder lake, yellow ochre, burnt sienna, lead white, and prussian blue. [Report of McCrone Research Associates Ltd dated 23 November 1983].
The paint between the Heads was found to differ from all other samples in that it is discrete, thickly applied and showed no evidence of any paint strata. [Report of Henry Bland dated 2 August 1999].
Examination by scanning electron microscope revealed that the paint layer is remarkably thin - approximately 10 microns. In microphotographs of the cross-section of the paint layer can be seen several distinct and discrete strata of paint, usually three, having the character of thin glazes. No evidence of pigment particles was found in the blue paint layer. [Report of UK Forensic Science Services Ltd dated 24 February 1988].
EDAX (Analysis for Prussian Blue)
The blue paint (from seven diverse blue areas of the painting) was submitted to elemental analysis by energy dispersive X-ray using an electron microprobe. No iron or other metal elements were discovered, apart from a few inclusions of lead derived from the ground. "No evidence of Prussian blue was found in any of the paint flakes examined". [Report of Cambridge Environmental Research Consultants Ltd dated 22 February 1988].
The absence of any metal elements and pigment particles in the blue paint (in fragments randomly taken from seven different areas of the painting) was considered to point to the use of an organic, vegetable-derived dye. Research in 'The Materials and Techniques of Medieval Painting' - Thompson (1956) and 'Painting Materials - A Short Encyclopaedia' - Gettens & Stout (1966), followed by a chemical test, found that the probable blue colouring agent was the medieval dye, turnsole or similar indicator dye. It was stated to have the property of changing colour with acid or alkali, red in acid and blue in alkali (similar to litmus). In view of the recorded colour change, a chemical test was performed on samples of the blue paint. "A slow colour change occurred in dilute acetic acid solution, the blue colour being lost to be replaced by an orange colour, while some finite red particles not previously visible leached out from the destroyed medium". [Report of UK Forensic Science Services Ltd dated 5 September 1988].
Analysis of blue paint test samples by High Performance Liquid Chromatography, together with the above analysis by SEM and EDAX, confirms that all other likely pigment material for the blue paint has been excluded. [Dr Jan Wouters, 25 March 2004].
Paint samples from the Tondo were subjected to laser Raman spectroscopic analysis in an attempt to identify the medium. Though the medium was not specifically identified, the Raman spectra were able to exclude the mediums of oil, resin, gum, glair and animal glue.
At the same time, the Raman Spectroscopy analysis identified use of the pigment massicot in the painting. "Clear evidence is seen for massicot, yellow lead (11) oxide, with Raman bands at 142, 287 and 380 cm1". [Report of Professor Howell Edwards, Professor of Molecular Spectroscopy dated 20 September 2004].
Infra-red and ultra-violet examination
Examination of the whole of the painted surface by these methods revealed no further information about the construction of the painting.
Read the Tondo Paint Materials Report from the UK Forensic Science Service.