Date of study: March 11–12, 2013
A research team at Columbia University consisting of Professor James T. Yardley of the Department of Electrical Engineering and Alexis Hagadorn, Head of Conservation, Columbia University Libraries, with the support of Dr. David Ratzan, Curator of the Papyri Collection, has utilized micro-Raman spectroscopy to investigate the chemical composition of pigments for selected regions on both sides of the manuscript fragment known as the Gospel of Jesus's Wife (GJW) and also for an additional fragment from the Gospel of John. These manuscripts were provided for the purposes of this study through Professor Karen King of Harvard University. Most dyes or pigments exhibit characteristic Raman spectra.18 Micro-Raman spectroscopy constitutes a non-destructive technique for characterizing the chemical composition of inks and pigments.19 In the Raman scattering process molecules within the exciting laser beam emit light with photon energy reduced (and therefore wavelength increased) by the amount of a characteristic vibrational motion of the molecule. Therefore the measurement of scattered light intensity as a function of wavelength provides direct information about the inks under investigation through the display of characteristic vibrational resonances or peaks. Black ink pigments generally fall into the categories of carbon black (many variations),20 iron gall,21 hematite,22 magnetite,23 and various iron oxides.24 Modern black inks are formulated using complex dye molecules that typically exhibit characteristic sharp spectral features.25 For black pigments based on forms of carbon black, the detailed spectral characteristics are somewhat dependent on specific pigment preparation as well as excitation wavelength.
For these manuscripts, we obtained micro-Raman spectra using a conventional commercial instrument (Renishaw inVia). We used 633 nm laser excitation (10 mWatt maximum power) using 0.5%–10% of the laser power focused onto the sample through a conventional ×100 microscope objective. We collected approximately 140 Raman spectra from selected regions of the two sides of the two manuscripts, examining in detail the Raman shift range from 150 cm−1 to 1900 cm−1. In a parallel study we have examined Raman spectra from over fifteen papyrus manuscripts from the Columbia collection covering the time period from 500 b.c.e. to +1000 c.e.26 The conclusions of this study for the GJW manuscript are as follows:
The inks used in this manuscript are primarily based on carbon black pigments such as “lamp black.” The observed Raman spectra are very similar to those of the carbon-based inks studied for a wide variety of manuscripts including many dating from the early centuries of the Christian era.
From the observed Raman spectra, we find no evidence for any constituents of ink or types of ink other than carbon black in the selected regions.
The ink or inks used in GJW are similar to, but distinct from, the ink used for the Gospel of John manuscript.
Within the available accuracy of our measurements, our data are consistent with a single ink composition for each individual side of the GJW manuscript.
The Raman spectra obtained from the “recto” side and from the “verso” side are indistinguishable within our experimental error.