Conservation Portfolio Home
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Material Investigation of 1937 Moroccan Ceilings and Doors from Doris Duke's Shangri La
In addition to conservation treatment on site, instrumental analysis was performed on samples at the Winterthur Scientific Research and Analysis Laboratory with the assistance of scientists Catherine Matsen and Dr. Chris Petersen. Cross-section analysis was also performed in collaboration with Richard Wolbers. Significant findings of this investigation were presented as part of a poster at the 2016 ICOM-CC Interim Meeting in Potsdam, Germany.
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Thumbnail of the poster presented at 2016 ICOM-CC Interim Meeting. The left side discusses material composition of the Moroccan ceiling and doors, its effect on condition, and conservation treatment. The right side discusses treatment of a 19th-century Syrian ceiling acquired by Doris Duke. Treatment was performed by my colleague, Nick Pedemonti. Subsequent images in this gallery will show details of the results summarized in the poster.
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Detail of decoration on foyer ceiling. Hardware used to join the panels may have blocked local areas from receiving varnish, such as the brighter circular area in the middle of this image. Note the bright yellow as well as the white of the outside right stripe. These colors are practically indistinguishable under the yellowed varnish coating.
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Cross section sample from a foyer ceiling fragment under visible light to observe the colors, order of paint application, and pigment particle size and shape.
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X-Ray Fluorescence spectroscopy (XRF) Results
To learn more about what pigments were used, I performed elemental analysis with Catherine Matsen. XRF data provides the pure elements that are present in the area of analysis under the X-ray beam. The presence of certain elements can suggest specific pigments, such as the presence of lead (Pb) in white decoration would suggest lead white (PbCO3)2Pb(OH)2
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X-Ray Fluorescence (XRF) spectrum taken on the surface of a fragment from the foyer ceiling (shown in upper left). Most of these elements are indicative of white pigments. Detection of lead (Pb) is also likely associated with the red lead ground seen in cross section. XRF does not discriminate between layers. The iron (Fe) is likely associated with dirt on the surface. See comparison in the next spectrum.
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XRF spectrum taken on area of exposed decoration (varnish missing). The main differences between this spectrum and the previous (including varnish) are no detection of iron (Fe) and less lead (Pb), which was commonly added to varnishes to improve drying.
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XRF spectrum taken on an area of green decoration. The lack of copper (Cu) and chromium (Cr) especially suggest that a synthetic green pigment was likely used.
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An overlay of two spectra taken from a sample that was suspected to have gilded decoration based on adjacent decoration in better condition. The results show that the black area is heavily tarnished tin (Sn) leaf that was toned to look like gold.
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Here is an example of the toned tin leaf still in good condition on the living room doors.
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Scanning Electron Microscopy- Energy Dispersive X-ray Spectroscopy (SEM-EDX)
Further elemental analysis was performed on cross section samples using SEM-EDX. This technique works similarly to detect elements present in the sample, but it is also able to map the distribution of elements within the sample.
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A cross section sample under a stereomicroscope in visible light.
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A detail of the previous cross section sample taken using SEM-EDX. The false colors indicate distribution of lead (Pb-blue) and barium (Ba-green) in the sample. The Pb mapping corresponds to the red paint layer in the previous visible light image.
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This is the same sample at a much higher magnification focusing on the top most white/yellow paint layers. The false color mapping shows a layer with a mixture of zinc (Zn-pink) and barium (Ba-green) suggesting the pigment lithopone BaSO4*ZnS. The presence of arsenic (As) is unusual because it is often associated with green pigments. This sample has yellow and white surface decoration. The arsenic could suggest the use of orpiment as yellow colorant.
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Investigating Organic Materials in the Composition
Organic materials of interest associated with painted surfaces are the binding media (which hold the pigments together as a paint) and the finish or later restoration coatings applied to the surface.
The elements in these materials (C, O, H) are light weight and not easily detected by XRF. It is the molecular structure and how these elements bond together that is uniquely identifiable. Alternative techniques look at fluorescence and bond characteristics in order to describe and identify these materials.
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Fourier Transform Infrared spectroscopy (FTIR) was used on a paint sample from the living room doors to analyze the pigment and the binder. These results compared to a reference spectra show that the pigment is barium white bound in a glue medium. Distemper (or animal glue paints) were traditionally used for this kind of decoration in Morocco in the 19th century.
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Cross-section analysis also indicated the use of oil medium. Fluorescent dyes that bind to specific material groups can be applied to the sample. Here is the same cross section under 550nm light before staining with the dye (left) and after applying Nile Red (right). The bright red fluorescence is a positive reaction for the presence of lipids. This paint layer is likely oil bound.
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This is the same cross section under 350nm light before staining (left) and after staining with TTC (Triphenyl Tetrazolium Chloride). The red-brown color indicates a positive reaction and the presence of carbohydrates in the same layer that was positive for lipids. This combination of results suggests the use of an emulsion paint
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Gas Chromatography-Mass Spectrometry performed by Dr. Chris Petersen was used to analyze samples of resinous material on the surface of the doors and ceilings.
Here is a chromatograph from a sample of peeling varnish. The results are consistent with an aged natural resin, likely pine.
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Other samples, such as this one from an area of bubbled resin showed a high content of sesquiterpene compounds.
These compounds are indicative of essential oils. Specific structures within the mass of sesquiterpene peaks were identified and found to be consistent with Cedrus atlantica, or true cedar of Lebanon, which was identified as the substrate material for all the Shangri La elements produced by the Rene Martin studio.
As illustrated above, it appears that extractives from within the wooden substrate have migrated to the surface, disrupting the paint and varnish layers, and sometimes mixing in with the varnish when depositing on the surface. Extractive bleed is a phenomenon encouraged by high humidity and temperature.
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Significant Conclusions:
- The disfiguring resin globules affecting the aesthetic condition are linked to the choice of material for the wooden substrate. Cedar wood is prone to extractive bleed especially in hot and humid environments, like Hawai'i. See how the conservation treatment was tailored to address this issue.
- Many decorative materials were consistent with traditional Moroccan craft practice, but the indication of synthetic pigments and emulsion paints suggest that Moroccan artisans were exposed to new developments in paint technology coming out of the West in the early 20th century.
