Standardized system for multispectral imaging of palimpsests

Understanding multispectral imaging of cultural heritage: Determining best practice in MSI analysis of historical artefacts

“…Materials such as inks and parchment interact with different wavelengths of light in various ways, for example, iron-gall ink reflects infrared light whereas carbon-based ink absorbs it [18]. MSI can differentiate between different inks and pigments [18][19][20], recover hidden features [21][22][23][24] and provide information on the current condition of an object [25][26], which can be useful for conservation practice.…”

“…Since then images have been captured for a range of historical artefacts in order to recover lost text and features, such as the Dead Sea Scrolls [21], [29], Petra and Herculaneum scrolls [22], the Archimedes Palimpsest [30], and the letters of David Livingstone [31]. It has been widely used to recover undertexts in palimpsests ( [23], [31]- [34]) as well as to locate watermarks in paper documents [35][36] and underdrawings in paintings [25], [37][38][39]. However, research into the optimal application of MSI in cultural heritage is still relatively scarce, and where it exists it tends to be specific to reporting the results of a particular artefact (see [30][31], [34], [40][41]).…”

“…Systems have progressively developed from illuminating the artefact under broadband illumination and selecting wavelengths using external filters fixed to the camera lens (see [18][19][20], [47][48]), to illuminating the artefact directly with narrowband light emitting diodes (LEDs) (see [23], [31], [35], [49][50][51]). The latter systems use filters to exclude the illumination light, allowing images to be acquired of the fluorescence (see [23], [34], [45], [52]). Although the systems themselves have developed (and the costs reduced) over time, the same processing techniques are still applied.…”

“…Therefore, documentation can be inconsistent due to the focus of the publication, and the objectives of the authors and institution carrying out the research. Furthermore, although many papers describe the imaging process for particular artefacts, such as palimpsests [23], ostraca [60], paintings [25] and carbonized papyri [22], collections usually contain a variety of artefacts. Consequently, a pipeline describing techniques is required to better understand what is currently meant by multispectral imaging in cultural heritage.…”

“…This conversation can reveal any misunderstandings and lead to agreement on handling the object and determining the most efficient imaging protocol. Research that focuses on multispectral imaging of a particular artefact or class of artefacts (such as carbonized papyri [22], [33], palimpsests [23], ostraca [60], [74] and paintings [25] and exposure to damage [47] enables heritage practitioners to determine whether MSI in general is appropriate. The optimal combination of wavelengths and filters depends on the research question and the artefact itself, however, little research is available [19], [20], [47].…”