ne obvious and easy start for illustrator op art experiments is a set of repeated lines. The basic set has lines of even weight or stroke size and even interval. The set looks oscillating if the interval and line weight are the same because your perception keeps trying to make them blend in optical mixture into a grey instead of black and white due to the law of prägnanz. If the line unit is too large in scale in relationship to the visual field, the effect will not work and if it is too small the optical mixture will take place and there will be no vibration. So the oscillation or vibration effects depend on a scale relationship to our perceptual functions. The brain calculates that it is looking at lines, then at greys, then at lines and a vibration ensues. The Meta effect is that the viewer realizes that the artwork functions in the brain, not on the canvas. Here are two Bridget Riley examples of line sets.
Bridget Riley, 1963, Fall
Bridget Riley
It is not too much of a stretch to realize that small jpgs of these on the web or printed in books do not have the effect of the original in front of one’s eyes, scaled by the artist.
Along with the line sets the artist introduces waves and changes in interval. Mostly what this does is changes the locations of where the thresholds of falling into optical mixture occur and increases a sense of motion. This can be done at the outset with repeated wavy lines or introduced later with tools like the warp tool in Illustrator.
The wave set below has a calligraphic line added and zigzag filter.
If two sets are overlapped, moirés will occur. The moiré effect is also an aspect of Prägnanz because it depends on the threshold at which the crossover angles between the line sets are clear to perceive and want to be ignored as being insignificant. This is also discussed in the Gestalt literature as leveling, sharpening and ambiguity. You can download interactive moiré demonstrations from Wolfram math world.
The line sets can be straight segments; waves, circles or whatever you may invent but the lines and intervals need to be equal- or very close to it.
Line blends can also result in moire. This is due to critical angles between lines that viewers want to see leveled or sharpened.
