The test conditions and environment were kept constant while
testing equally comparable materials or methods. In the tests
where we used our sample plate we always recorded the same fragments.
The outcome of ordinary photography was most difficult to optimize.
Considerable amount of time was spent in trying different
illumination conditions and suitable developing procedures before
the real test photographs.
Hundreds of negatives and paper copies were made. Simultaneously,
a test set of negatives from the real Petra Scrolls was being
scanned in different commercial litographic firms, with request
to produce the best possible pictures.
The amount of manual work and sensitivity to faults makes
photography less appealing when comparing to modern digital
imaging techniques described next.
The direct scanning method was also hard to test, because
a typical sample plate is larger than a typical A4- or U.S.Letter
sized flat scanner. Placed upon a scanner, the few millimeter
high edges of the scanner casing and the glass plate cause the
samples to be too high for the scanner to focus correctly.
So, the cover had to be taken
off, exposing the CCD cells to dust and voiding the warranty.
Opening the cover of a scanner has to be done with special
care and in a dustless environment. The first dust
particle landing on the CCD will cause a line to appear in
all further scans, and several will render the scanner
The same illumination problems we had with photography were
also present when testing the video grabbers. Fortunately,
the result could be seen in real time, and so the lights
could be adjusted to optimum quite easily. Also, with a special
type of CCD sensor element, we were able to stretch the usable
band of spectrum to near-infrared area.
The red and infrared filters were applied to these tests, too.
The electronics (amplification, white level) of the camera
itself were slightly modified to give best results.
Two different thermographic cameras were tested; the glass plate
effectively prevented the camera to detect the differences
of temperature or emissivicity in the fragments. Slight heating
to approximately 45°C with a tungsten lamp did not help
We used Helsinki University Central Hospital's X-ray
equipment to search for differences in density.
The glass plate captured X-rays far more efficiently
than the thin, soft papyri fragments. Several variations
in power and exposure times gave, at best, flat
grey pictures without a single detail.
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Antti Nurminen, 34044T, email@example.com