Suminagashi is an ancient Japanese marbling art involving floating ink on water and taking a print from it. Suminagashi literally means ‘floating ink’. Drops of ink and dispersant are interspersed so that they spread out in ripple patterns on the water, as you can see in the highly speeded up and clipped video below. I also have a tutorial here.
Traditional suminagashi uses Indian ink, floated on water with no thickening agent, and then transferred onto absorbent Japanese paper. Traditional suminagashi is therefore black on white, but one can still get an enormous range of looks and patterns from this. The long silk scarves in the gallery below all use the suminagashi technique, in black and white and in colour.
The Shimauma scarf has been tightly twisted from both ends and then wrapped twice around the neck and tied at the back. 
The Shimauma scarf in a smiple knot 
The Kokeko scarf, folded in two with the ends tucked through the fold. 
Wakumi scarf with the ends tied and wrapped as a ‘mock infinity’ scarf. 
Midori scarf draped
Transferring the technique to fabric requires using a mordant to allow the inks to be absorbed onto the silk or other fabric, and because this works differently to absorbent paper, the results are a bit less predictable. Some inks that look vibrant floating on the water produce almost no print on fabric, while others are fine. A lot of experimentation is required.
To create a long silk scarf, a lot of ink and patience is required, as the more ink ripples are put into a pattern, the stronger the colour will usually be, and it takes a lot of colour to fill a marbling bath to fit a long scarf!