curved banding

Scallop and Clam Shells

Creating a Serpentine Marbling pattern was not much of a challenge because the folds did not branch and merge. Some patterns look as though the tines meet and separate.

One beautiful marbling pattern used for endpapers looks like an array of patterned scallop shells. With their sinews splitting and merging, it is difficult to see how such patterns are generated. Dan St. John of Chena River Marblers was kind enough to explain that this pattern is produced by sinusoidal motion of a comb having two sets of tines offset both in the direction and perpendicular to the direction of the stroke.

Splitting the offset comb into two parts and stroking each separately allows these patterns to be produced with the tools already developed.

In the progression below, the contents of the PostScript procedure Composite-map are displayed with the change from the previous contents in red. Composite-map takes an x and y coordinate pair on the stack and leaves the transformed x and y on the stack.

Here are ink circles stroked upward with a fine-toothed comb.

The first line moves the center of the ink-circles to the centerline of the drawing; and down to counteract the upward drag of the combing.

Make horizontal sinusoidal displacements like the serpentine case.

Stroke two tines straight upward.

Subtract the sinusoidal displacement; now those last two strokes are sinusoidal.

Now apply the opposite horizontal sinusoidal displacement.

One displacement of -90*sin replaces two displacements of -45*sin.

Stroke three tines straight upward.

The third tine is off-screen to the right.

Finally, subtract the sinusoidal displacement.

[image is linked to PostScript file]


Reversing the direction of the initial combing results in a variant looking more like giant clam shells.

[image is linked to PostScript file]

Reversing the direction of the final combing results in a variant like a book cover I have seen.

[image is linked to PostScript file]

The dense crowding of contours in this pattern makes the sinusoidal channels speckled when raster-rendered.

[image is linked to PostScript file]

Oversampling by a factor of two in both directions reduces the speckling significantly.

Drawing the contours rather than filling them makes images resembling topographic maps. This image is oversampled.

Looking at a print of the entire projection of the ink circles, Carl Mikkelsen noticed that outlines of the top and bottom of the figure are similar. This naturally leads to the next chapter, which extends marbling to a two-dimensional manifold.

Copyright © 2004, 2007, 2010, 2016 Aubrey Jaffer

I am a guest and not a member of the MIT Computer Science and Artificial Intelligence Laboratory.  My actions and comments do not reflect in any way on MIT.
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