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Multispectral imaging

Introduction | Procedure | Results 1 | 2 | 3

Part of a badly damaged Biblical fragment on parchment (Romans 14.8-9). Move the mouse pointer over the image to display the text revealed by multispectral imaging in the infra-red region. For further options, see the instructions below.

The multispectral imaging process, perfected on the Herculaneum papyri since 1999, rapidly captures a series of high-definition digital images at different ranges of the light spectrum by means of an automated, rotating wheel containing around 25 filters which are passed in succession in front of the camera's lens. The process seemed to work best on darkened, charred, or stained surfaces, and can image through some surface materials, but sees nothing through mud, clay, or silt. It produced excellent results on palimpsests, cancellations, and erasures due to damnatio memoriae, and on disintegrating surfaces where the ink has settled deep into the fibres. It was least successful on surfaces that were partially or entirely washed out. On abraded and uneven surfaces the camera's long depth of field elides differences in levels and aids reading by eliminating all shadows and levelling so that all writing appears well-defined as though on a single layer. Darkened surfaces tended to respond best deep in the infra-red range (c. 800-1000 nanometres), but not exclusively so: each papyrus and surface (and sometimes parts of each) responds best (i.e. with maximum reflectivity, contrast, and definition, so that background noise is eliminated) at a different point (which must be located) in the spectrum, including some in the ultra-violet range. Surprisingly, in one trial the process successfully imaged through painted gesso, revealing a previously unknown document (report to a strategos) on the papyrus cartonnage surface underneath.

In many cases, images taken at one point within the spectrum, the point giving the greatest contrast between ink and papyrus surface, are sufficient for study. But contrast can be enhanced still further, where necessary, by putting together information from images taken across the whole spectrum. For example, iron-gall ink displays a characteristic pattern of responses, going from being transparent in the infra-red region to being at its most visible in the ultra-violet. A computer can be instructed to display only the pixels that show that characteristic response and discard the rest: the result is that shadows and dark papyrus fibres, which can sometimes be confused with ink in images taken at a single point on the spectrum, do not show up at all.

USING THE FLASH PRESENTATION

Advanced options, including 'zoom' and 'rewind', are available from the Flash menu. To bring up the menu (shown here), click on the image with the right-hand mouse button (Windows users) or click on the image with the mouse button while holding down the 'ctrl'/'control' key (Macintosh users).

Once you have zoomed in, you can move around inside the image by clicking the mouse button (the left-hand mouse button for Windows users) and moving the mouse in the direction desired while keeping the button depressed. (You may first need to select 'Forward' from the Flash menu, as described above.)