AIC's 44th Annual Meeting

The dry climate of Egypt has preserved thousands of handwritten documents and books, from the Old Kingdom to the Middle Ages, that can provide insight into our understanding of ancient cultures. Unfortunately, in most cases the dates of these manuscripts are unknown, although several document types bear precise dates, often to the day. For the undated manuscripts, the only current scientific method of estimating the date of writing is radiocarbon dating, but these measurements are destructive and cannot be practically used to date the media as separate from the support. In contrast, micro-Raman spectroscopy, a non-destructive light scattering technique, can be used to distinguish physical and chemical properties of materials. We have discovered that, for a study of well-dated ancient Egyptian papyri covering the date range from 300 BCE to 900 CE, the Raman spectra (25 to 40 measurements on each manuscript) of black ink all show the characteristic spectrum of carbon black materials. The spectrum of carbon black is characterized by two broad features, the G and D bands. The G band at 1585 cm-1 is a Raman allowed transition that arises from the E2g in-plane vibration of sp2 bonded carbon. The D band is a forbidden Raman transition that occurs when the lattice symmetry is broken. The D band at approximately 1350 cm-1 is associated with disorder, vacancies, crystalline edges, etc. The broad spectroscopic features are indicative of crystalline and amorphous carbon. We observed the carbon black spectra exhibit systematic change as a function of manuscript date. This observation is unexpected given the dates of these papyri cover a 1,200-year time span and the fact that each manuscript has a unique provenance, archeological, and storage history. We conclude that, over this time-period, black ink pigments in Egypt were manufactured using similar processes. We attribute the systematic change we observe in the Raman spectrum to two concurrent oxidation processes: slow oxidation of the crystalline carbon and faster oxidation of the amorphous carbon. The changes we observed are well characterized by models for carbon black Raman spectra that relate the relative intensity of the D to the G peak to defect density in accordance with oxidation. Oxidative degradation must proceed relatively uniformly over time to alter the Raman response of the material, providing a direct experimental indicator for manuscript age. Using this technique, we have been able to distinguish between the Raman spectra of different carbon-based manuscript inks on ancient Egyptian documents. Most importantly, this research establishes the basis for a simple, rapid, non-destructive method for dating ancient manuscripts from Egypt as well as the ability to differentiating between modern forgeries and authentically ancient manuscripts.