The basic process for applying walnut ink to create unique backgrounds
is shown below.
Note that the walnut ink crystals should be dissolved in warm water. Make a fairly concentrated solution (which will be dark) because the process uses water to create lots of light areas.
It is easier to lighten a piece after you have painted it, but more difficult to darken it if you have started with a very dilute solution.
Here's what you will need:
Walnut ink crystals
Printmaking paper (Rives BFK was used in this example, but Arches, etc. would also work well). Really absorbent watercolor paper doesn't work as well because it tends to absorb the walnut ink. What you want is paper that will allow the ink to move when water, bleach or a resist is applied.
Water (a spray or squirt bottle to apply this with is also helpful to control the size of the "dots" that you get).
Calligraphy ink or acrylic ink (if you want to make a design on the paper first; optional, but can add to the overall effect).
See photos for step by step instructions.