Prep the surface or wall. Use a damp rag to remove any residue or dust. Allow the surface to dry.
Apply a light-colored neutral base color. White, pale yellow or tan works well. Let it dry completely.
Choose at least two contrasting paint colors.
Use a paint roller, appropriately sized for the object or wall, to apply the lighter color first. Paint in long curves, like that of a stream, in the same direction. It should not look uniform. The curves of paint do not always need to touch; there should be a good amount of the base coat showing through between the curvy strokes of paint.
Introduce the next color, the darker color, with a rag by dabbing it onto the surface in thick or thin sporadic lines. It should look randomly spaced.
Go back over the freshly painted darker lines with the roller, dipped back into the lighter color, to soften them.
Take a dry brush and softly go back and forth over the fresh paint in random directions to blend it together slightly. You will still see the swirls of marbleized color.
Lightly press sheets of plastic wrap on and off the surface in random spots while the paint is still wet, going in a similar diagonal direction, until the desired marbling effect is produced.
Lightly dab with another dry brush in random directions to soften the marbling.
Dip a feather in a little bit of a water and trickle several veins through the surface before it dries.
Soften with a dry brush.
Allow the paint to dry completely.