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How were the circles drawn?
- How were the circles drawn?
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How were the circles drawn?
Jorge_Stolfi > 5 hours ago
How were circles in the Cosmo and Zodiac sections drawn?
The general smoothness of the traces indicates that they were drawn with some mechanical implement, rather than by free hand. In several (all?) pages one can find a pin prick at or very close to the center of all the circles on the page, consistent with the circles being drawn with a compass.
However, in many cases the circles are not quite round. Typically, in an image editor like Gimp one can get a geometrical ellipse that matches, say, 3/4 of the circle very precisely, down to a pixel or two in the BL 2014 images, with a center that is a few pixels away from that pinprick. The height and width of the ellipse may differ by up to 2% for the larger circles. This discrepancy is probably due to the parch not being flat when it was imaged.
But other parts of the circle will then deviate from that geometric ellipse by several mm over spans of several cm. Worse still, the drawn circle often fails to close: the two ends miss each other by a couple of mm and run parallel for a few cm.
Some of these deviations could be explained by the parch being not just curved but badly warped when it was imaged. But this cannot account for the circles that don't close. Possible explanations for these errors could be the parch moving and warping while the circle was being drawn by the Scribe, or the compass being some improvised contraption that was not as solid as it should have been.
The traces of the circles are very thin, only 0.2 mm or less wide. Some of the traces are continuous but very faint, to the point of being partly invisible in the BL 2014 images. They may have been drawn with a hard pencil-type point, such as a lead (real Pb) pencil.
In some pages, these "pencil" traces were apparently retraced in ink by hand, resulting in a visibly jittery double trace; but these cases are better discussed in the context of general retracing discussion.
But in many cases the "pencil" traces alternate with thin ink traces, with no deviation. The ink traces are just as thin as the pencil ones. They are sometimes continuous too, but sometimes break down in random dashes and dots.
Therefore, I believe that the full circles were drawn with a compass with a pen-like attachment. The parts that look like drawn in pencil must be where this attachment basically ran out of ink and merely scratched the parch, leaving just a smudge of whatever little ink that was still adhering to it.
The attachment cannot have been an ordinary quill pen, because that would surely have produced much broader traces. Today compasses usually come with special pens for ink, like You are not allowed to view links. Register or Login to view.. This tool can draw very fine lines and was massively used for technical drafting (including by me, in high school and college) until ~40 years ago when laser printers became available.
The screw with knurled nut, visible in that mage, lets one vary the thickness of the trace. It can be dispensed with if one only needs traces of a fixed width. All one needs is a tweezer-like pair of steel prongs with properly shaped tips, that can hold a drop of ink between them by surface tension
This compass accessory must have been widely available at least since the 1800s. But would it (or something equivalent) be commonly available to scribes in the 1400s? Centuries before steel pens became common? The need for it surely was there...
Does anyone know?
All the best, --jorge -
RE: How were the circles drawn?
Bluetoes101 > 3 hours ago
Janky free online tool used for measurements, not quite accurate but shows well enough
There was another thread from a while back on the same subject and once you know to look for tool marks in the middle you spot a fair few