42nd Annual Meeting – Research and Technical Studies (RATS) Session, May 29, "Unwrapping Layers in Historic Artworks: Virtual Cross-Sections with Pump-Probe Microscopy" by Tana Villafana

For the last few years, Ms. Villafana and her co-authors have been refining a new microscopy technique for conservation to create “virtual” non-destructive cross-sections. This is a very exciting development for our field, particularly for those of us working with materials–such as works of art on paper–that don’t typically allow for sampling. And for paintings conservators more accustomed to taking traditional cross-sections, this technique has promise for in-situ analysis of paint layers through varnish.

To summarize, the virtual cross-section image is created using pumpprobe microscopy, a non-linear optical microscopy technique developed for the biomedical field, which allows non-invasive detection of biological pigments indicative of skin cancer. Because skin tissue is highly scattering, this technique was developed to be inherently confocal, meaning that the signal is generated only at the focal point, creating less scattering, and less spectral noise. The approach is naturally suited to the highly scattering pigments, binders, and supports making up materials of cultural heritage. However, the complexity of art objects render the technique more difficult to apply.

Pumpprobe microscopy achieves high resolution in three dimensions with a maximum image area of up to 1mm square. The penetrating depth ultimately depends on the material composition of the object under study. The technique is typically operated at two wavelengths: 810nm and 720nm and modulated to create a series of images at different inter-pulse delays. These images can then be colored according to the molecular composition of the specific material and stacked to create a 3D rendering.
With this presentation, Ms. Villafana shared case studies illustrating ongoing research into cultural heritage materials using pumpprobe microscopy. The first project investigates applications of pumpprobe on paper substrates bearing coatings of lapis lazuli pigment. With this technique, it is possible to produce an image illustrating the physical structure and condition of paper fibers underlying the paint layer. She observes that the pigment particles cluster around the fibers, as seen in the slide below. She is interested in further investigating the natural heterogeneity of lapis lazuli crystals, noting that samples from different parts of the world exhibit different delay behaviors. She plans to complement her pumpprobe analysis of lapis lazuli pigments with SEM-EDS, Raman, and FTIR.
villafana_paper-lapis villafana_lapis-pump-probe
Villafana also presented on preliminary research using pumpprobe to investigate historical methods of pottery manufacture. After finding that pumpprobe delays of hematite are dependent on firing temperature, Ms. Villafana started using mock-up clay bodies fired under different conditions (Oxidized at 1800F and 2300F/Reduced at 1800F and 2300F) to examine the difference in delay behaviors from the exterior to the interior of fired clay. She has found that higher temperatures and oxidation both result in shorter lifetimes. Further study will focus on phase change and particle size.
I quite curious to see how this technique develops in the near future. Will pump-probe (or something like it) be able to replace traditional cross section techniques within the next 5 to 10 years? What other techniques are being developed out there that might be able to achieve similar results?
See the following two links for more information:
Villafana, et al., full-text PDF of recent research published in The Proceedings of the National Academy of Sciences of the United States of America
Article about Pump-Probe Microscopy in Science News, from Science, AAAS

AIC’s 40th Annual Meeting, Book and Paper Session, May 9 “The Mysterious Voynich Manuscript:  Collaboration yields new insights”

The Mysterious “Voynich Manuscript”: Collaboration Yields New Insights.  Paula Zyats, Assistant Chief Conservator, Yale University Libraries; Gregory W.L. Hodgins, National Science Foundation—Arizona Accelerator Mass Spectrometry (AMS) Laboratory, University of Arizona; Joseph G. Barabe, Senior Research Microscopist, Director of Scientific Imaging,  McCrone Associates, Inc.

The Voynich manuscript, also known as “The Book That Can’t Be Read”, was donated to Yale in 1969. It is a vellum manuscript, bound in limp vellum (the binding is probably not contemporary, according to Paula Zyats), and is of unknown origin. It is written in either code or an unknown language and contains fantastic and garish illustrations. There have been a number of theories as to who authored this work, ranging from Francis Bacon, Leonardo Da Vinci, to Voynich himself. 

This presentation described the materials analysis and conservation treatment that were undertaken, partly as a result of a proposal by an Austrian film crew in 2008, to discover more about the creation of this work. Curators, conservators, and scientists collaborated to sample portions of the manuscript in order to identify and date the inks, paints, and parchment used in the manuscript. The manuscript was in good condition and conservation treatment focused on stabilization. Some fold-outs had cracks and tears needing repair, and some corners were turned up.

Carbon dating at the National Science Foundation—Arizona Accelerator Mass Spectrometry (AMS) Laboratory at the University of Arizona revealed that the parchment used for the folios dated to the 1450’s. Analyses by McCrone Associates suggest the drawing and writing inks are from the same period. Numbers on the folios were from a later period, but it was determined there are no modern components in the volume.

The Beinecke Library has made digital images of the manuscript available at:


The documentary can be accessed at: http://documentarystorm.com/the-book-that-cant-be-read/

And, Renee Zandbergen has a comprehensive website describing this work: http://www.voynich.nu/

Ms. Zyats expressed her initial surprise that Yale agreed to this project, and there was some discussion about libraries and museums being willing to promote unique items in their collections. There is an understandable reluctance to market these materials since that may increase their handling and use. Rather than acting as a substitute, digital images often serve to increase curiosity about the real artifact. Nonetheless, it is exciting for conservators, scholars and the general public to learn more about the provenance and materials of such a unique item.