Technique · Geometry
Ink jellyfish
A pen-and-ink jellyfish: a ribbed, hatched bell with a scalloped rim, frilled oral arms and long hair-fine tentacles on pale paper.
Ink jellyfish is drawn geometry, rebuilt as it changes. Every piece on Synapse Drip is made from a recipe that layers techniques like this one, and you can change any of it in the Studio.
Good to know
- A jellyfish pulses by contracting the muscles in the rim of its bell, and the bell springs back on its own, as an elastic umbrella would.
- Many jellyfish are almost transparent, which is why an illustrator must draw them with line and hatching rather than with solid tone.
- The long tentacles of some jellyfish stretch many times the length of the bell; a lion's mane jellyfish that washed ashore in Massachusetts Bay in 1870 was reported to have tentacles about 37 metres, 120 feet, long.
- The frilled arms of a jellyfish carry food to its mouth, which sits on the underside in the middle of the bell; the one opening serves for eating and for getting rid of waste.
- The scalloped lobes on the rim of the bell are called lappets; between them sit tiny sense organs, rhopalia, that hold a balance stone and, in some species, simple eyes.
The mathematics
- The ribs are equally spaced in azimuth phi and drawn at x = r sin(phi), so the gap between neighbours is proportional to cos(phi): wide at the middle of the bell and closing up toward the edges, as ribs on a real dome do when seen from the side; here there are 20.
- The frills on an arm are a trochoid: the edge moves sideways by a sine and along the arm by a cosine of the same phase, which for a large enough amplitude makes the line loop back on itself.
- A hand-drawn feel is a small, slowly varying wobble in each line's width, produced by a product of two sine waves with unrelated frequencies, which never repeats visibly.
In art
- Pen and ink is the engraver's medium: tone must be built from lines, from hatching and cross-hatching, as Albrecht Durer did in the early sixteenth century.
- Scientific illustrators drew in pen and ink because it reproduces cleanly in print, and a few strokes can show both the structure and the texture of a specimen.
More ways to use it
Related techniques
L-system · Space colonisation · Diffusion-limited aggregation · Flow ribbons · Ridgelines · Curve families · Streamlines · Paint strokes