Imaging the Third Dimension of the Archimedes Palimpsest

摘要

Data produced by conventional 2-dimensional imaging of manuscripts having surface relief can be augmented by use of techniques that measure the out-of-plane characteristics of the manuscript leaves. The third spatial dimension can additionally provide information regarding the arrangement of layered or successively deposited materials. Confocal microscopy allows exquisite lateral and depth resolution, and is an ideal tool for measurement of surface topography and for building a detailed 3-dimensional model of translucent materials and structures. Our investigation of the Archimedes Palimpsest has utilized confocal microscopy to probe the distribution of faint remnants of 10th century (Archimedean) undertext, 12th century overtext, and more recent forged paintings. Image stacks are assembled from 2-dimensional confocal images acquired at different depths, and adjacent stacks are mosaiced to give a volumetric model of regions of selected regions of interest within the palimpsest's leaves. In particular, visible spectrum (533 nm) images obtained using confocal microscopy are used to examine different strata of substrate, text, and paint in folios containing 20th century forged paintings. These data are used to improve recognition of the different classes of content. Because confocal microscopy typically utilizes high magnification (5x or greater) and a limited field of view (typically less than 1 cm x 1 cm), confocal imaging of large areas must take into account the computational resources needed to combine and process the large data sets involved. In this paper we discuss confocal microscopy methodologies, tools, and wavelengths that address these issues and are appropriate for measurement of materials in museum and library collections.