Conservation Portfolio Home
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Data and Summary of Paint Analysis
Following is a summary of significant results from material analysis as well as a discussion of the research methodology. For more comprehensive data and a detailed interpretation of results please refer to the final report.
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These are the two buffets in the parlor at Stenton that were the subjects of this study. Buffet (a) is on the left (also known as the "sunrise arch" buffet). Buffet (b) is on the right.
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One of the curatorial questions at the onset of this project was whether or not both buffets were installed at the same time in the room. It appears that they were because the same early layers are present on cross sections taken from Buffet (a) and Buffet (b).
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Sample from second shelf from bottom at right side of Buffet (a) at moulding. 250X
Green paint goes right into wood pores.
It seems that the lower shelves on both buffets were completely scraped down/chemically stripped at some point. The paint layers directly above the wooden substrate correspond to some of the last layers (more recent generations) in other cross sections.
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Sample from left side of bottom shelf of Buffet (b) at moulding. 100X
Green paint flows into chip in wooden substrate.
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Was there a Polychrome Decorative Scheme?
It seems that during more than one generation moulding on the front of the shelves of both buffets and fluting in the arch of Buffet (a) were treated differently than the rest of the surfaces. The light pink layer in the sample from the background is missing in samples from the moulding on the shelves. Instead a layer of white aligns with this part of the stratigraphy.
See a visual representation of possible paint schemes through various generations here.
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Comparison of sample from background to a sample from the moulding on Buffet (a).
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Corresponding to the blue paint layer of the background samples is a more complex sequence for the moulding that suggests some sort of faux graining or marbling.
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The "Sunrise Arch"
Buffet (a) has slightly more elaborate woodworking with a fluted niche with star at the top. Only samples taken from this area had evidence of a gilded presentation surface.
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One of the cross section samples with noticeable gold-colored particles was analyzed using XRF before casting. The resulting spectrum showed a significant peak for copper but none for gold or silver indicating that this is likely bronze paint or leaf. The morphology points to copper alloy leaf.
Analysis was performed at the Winterthur Scientific Research and Analysis Laboratory by Catherine Matsen using an ArtTAX uXRF spectrometer at
600μA current, 50kV voltage, 100 seconds live time irradiation, with an approximately 70-100 micron spot size
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Scanning Electron Microscopy-Energy Dispersive X-ray spectroscopy (SEM-EDX)
SEM-EDX is helpful to identify elements present in a sample. Mapping capabilities can often pinpoint specific elements to certain layers within the sample. A conservator's knowledge of paint history and technology is used to draw conclusions about what pigments were used and relative dates of each layer.
Associate Scientist at the Winterthur Scientific Research and Analysis Laboratory, Catherine Matsen, performed the analysis for this project.
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With this project, many of the layers were composed of mixtures of one or more pigments. SEM-EDX was not as useful for identification of pigment compounds. The blue and green paints seem to have very little colorant (mostly lead white or calcium-based).
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One specific question was if the two green layers were the same. With overall mapping it was challenging to resolve the specific lower layer of green paint. Spot analysis was performed as suggested that chromium (Cr) was present in the upper layer, but not the lower layer.
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Raman Spectroscopy
This is a molecular analysis technique that allows for identification of specific compounds such as pigments. Analysis can be isolated to specific layers within a cross section.
Associate Scientist at the Winterthur Scientific Research and Analysis Laboratory, Catherine Matsen, performed the analysis for this project.
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Raman analysis of a yellow particle in the upper green layer confirmed the use of chrome yellow, which was not commercially available until 1814.
RED spectrum is from the sample area
GREEN spectrum is a reference for lead white
PURPLE spectrum is a reference for chrome yellow. Note how the peaks align with the red spectrum from the sample.
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Raman analysis within the same upper green layer looking at non-yellow pigment.
There is evidence that Prussian blue (BLUE reference spectrum) is present as well as calcium carbonate (GREEN reference spectrum). Again RED spectrum is from the sample.
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Raman spectroscopy confirmed that chrome yellow is NOT present in the lower green layer. This layer was likely applied prior to 1814.
The only definitive peak in the sample spectrum (RED) aligns with a known peak for lead white. A yellow earth (like ochre) was likely used to make the green, but this was not able to be confirmed with SEM-EDX or Raman probably because of the small amount of colorant used.
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The yellow layer present in samples from the "Sunrise Arch" was also confirmed with Raman to be composed of chrome yellow and lead white, dating this color scheme to post-1814.
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The blue layer applied to molding on the buffets and may be part of a graining scheme was identified with Raman as Prussian blue. One drawback of using Raman spectroscopy is significant fluorescence interference from binding media in paint samples. Catherine Matsen, and other scientists that have experience reviewing spectra are able to identify significant peaks despite some of the noise in the spectrum.
RED spectrum is from the sample and BLUE spectrum is a reference for Prussian blue.
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Interpretation of Data
Simply knowing the elements or compounds present is not extremely useful without being able to contextualize that information. Knowledge of when pigments were first discovered and available for market as well as historical trends in decoration are useful to relatively date the layers and paint campaigns.
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This type of overlay of historical generations/ periods onto the paint sample is often used to help summarize results.
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Descriptive charts are also used to present paint analysis results. More visual presentation of the data from this project was created using elevation drawings.
