New scroll, new challenges. First, we were pretty sure that our scroll is two-sides written, same as the scrolls we processed before. The further analysis revealed that this parchment is one (OUTSIDE) side written, with lots of confusing bright spots of the metal dust on both sides of the parchment. Also we noticed the inside parchment surface generally is much brighter than the outside surface, with the intensity close to the ink intensity.
Slice from the top of the scroll with a tightly connected metal strip
The next challenge was the metal strip, which has the same intensity as the ink, and very tight connected with the parchment near the top edge of the scroll. Although we can track the strip and remove it as a separate object in a similar way as we did for the two pages scroll, there are messy areas which impossible to separate without leaving parts of the strip on the parchment.
After the automatic unrolling the result looked promising, but not very readable:
After another week of experiments with the local segmentation, filtering, postprocessing and interpretation, almost everything become readable. The scroll appears to be an old, property related legal document. As one can see on the original photos , the parchment is the cut fragment, words are missing from both sides, left and right.
In December 2011 David and Graham visited the Norfolk Archives, based in Norwich, to discuss the Apocalypto project with Antoinette Curtis and her conservation staff. To assist in our initial scanning and virtual unrolling experiments, the Norfolk Archives graciously donated some non-accessioned objects of parchment with manuscript using iron gall ink.
One of the items is a small roll of parchment, that would be very damaging to unroll in order to read or photograph by conventional means. It is long and thin and in a damaged state that makes it impossible to unroll to read. This immediately attracted our attention, as it would be a real test of our ability to read an otherwise unreadable document.
The scroll was scanned in our MuCAT-2 microCT xray scanner with a 30 kV X-ray spectrum. Once the scan data was mathematically reconstructed, we could start to explore the scroll.
The first thing we noticed in the x-ray cross-section images is the metallic foil strip glued to the inner edge of the parchment. This shows as the bright shape at the top of the scroll in the image to the left. We can also see indications of the iron gall ink, again these show as brighter areas along the line of the parchment surface. The inset image shows a view along part of a letter on the surface. The high curvature and short depth of field of the scanned slices means that only a portion of the letter can be seen.
Volume rendering the scan data and virtually removing the parchment reveals the metal components of the scroll. Applying volume rendering techniques to the scan data and virtually removing the parchment, we can explore just the ink and metallic components of the scroll.
The lime used in the manufacture of parchment also shows up well because of its calcium content which is a metal. Excessive liming of the parchment can mask the visibility of ink in the x-ray scans; however in this case, while it shows up as a mass of spots and general noise in the image, the ink is still easily visible.
Adding back the parchment in the volume render of the scan data allows us to see the ink on the parchment. Due to the highly curved surface of the scroll, it’s impossible to read more than a few letters of a word using this technique.
The text on the rendered scroll looks faded and delaminated. This is because the distribution of iron in the ink isn’t uniform, and it’s only the iron in the ink that provides contrast in the x-ray images.
For a full unrolling, the data was passed to Oksana and Paul, our colleagues at the School of Computer Science & Informatics at Cardiff University. They will take up the story from here.