(I also blogged about this on
in illo tempore at
'The
Hunt of the Unicorn' tapestries' renovation reveals ....)
A
15th Century Find in Manhattan at
Steve Goddard's History Wire
points to
Capturing
the Unicorn by Richard Preston, also available in the April 11,
2005, issue of
The New Yorker. From
Capturing the
Unicorn:
At some point, the backs of the tapestries had been
covered with linen. The backings, which protect the tapestries and
help to support them when they hang on a wall, were turning brown
and brittle, and had to be replaced. Using tweezers and magnifying
lenses, [lead conservator Kathrin] Colburn and her team delicately
removed the threads that held each backing in place. As the
conservators lifted the backing away, inch by inch, they felt a
growing sense of awe. The backs were almost perfect mirror images
of the fronts, but the colors were different. Compared with the
fronts, they were unfaded: incredibly bright, rich, and deep, more
subtle and natural-looking. The backs of the tapestries had, after
all, been exposed to very little sunlight in five hundred years.
Nobody alive at the Met, it seems, had seen them this way.
...
Philippe de Montebello, the director of the museum, declared that
the Unicorn tapestries must be photographed on both sides, to
preserve a record of the colors and the mirror images. Colburn and
her associates would soon put new backing material on them, made of
cotton sateen. Once they were rehung at the Cloisters, it might be
a century or more before the true colors of the tapestries would be
seen again. ...
It took two weeks to photograph the tapestries. When the job was
done, every thread in every tile was crystal-clear, and the
individual twisted strands that made up individual threads were
often visible, too. The data for the digital images, which
consisted entirely of numbers, filled more than two hundred CDs.
With other, smaller works of art, Bridgers and her team had been
able to load digital tiles into a computer's hard drives and
memory, and then manipulate them into a complete mosaic -- into a
seamless image -- using Adobe Photoshop software. But with the
tapestries that simply wouldn't work. When they tried to assemble
the tiles, they found that the files were too large and too complex
to manage. ...
Two mathematicians, brothers Gregory and David Chudnovsky at first
used a 'cluster of nodes' supercomputer they had assembled from
mail order parts, in an attempt to join the tiles. But they
wouldn't match: 'the warp and weft threads didn't run smoothly from
one tile to the next. The differences were vast. It was as if a
tapestry had not been the same object from one moment to the next
as it was being photographed.'
Because the tapestry had been hanging vertically for centuries, but
was photographed flat on the floor of the museum's lab, the threads
began to relax, 'breath[ing], expanding, contracting, shifting. It
was as if, when the conservators removed the backing, the
tapestries had woken up. The threads twisted and rotated
restlessly. Tiny changes in temperature and humidity in the room
had caused the tapestries to shrink or expand from hour to hour,
from minute to minute. The gold- and silver-wrapped threads changed
shape at different speeds and in different ways from the wool and
silk threads.'
How to solve the problem of calculating changes in the tapestry, in
order to match the image tiles? Here the article is maddeningly
terse, referring to calculations of each pixel's relationship to
all nearby pixels, billions and billions of calculations. AFAICT,
The New Yorker doesn't disclose Preston's email address, so
surface mail or a telephone call are how to contact him for further
information.
Another 'wonderful thing' a la Howard Carter and Lord
Carnarvon.