Ink and Surface Tension
[S3 Physics and Up: Surface Tension]
I really don't have to explain much of this. Video speaks for itself.
It's probable that the chemical composition of the dyes themselves could have influenced the way the ink diffuses, since surface tension applies not only to water but every fluid medium with enough cohesion. Some could have been made with metal ions that are electrically charged by the kinetic reactions, which helped to keep the ink cohesive enough to stay together on the water's surface. What are your thoughts on this phenomenon?