On a large plate, in a circle, squeeze out water based paints (at least 5 to 6 different colors). In the middle of the plate add a water based conditioner (Floetrol). With a torn piece of cardboard, about 3 inches wide, swirl colors and conditioner onto large sheet of ordinary paper.
When dry, cut into sizes appropriate for cards. Glue onto cards. Now you are ready to embellish further. Don't forget to sign your art.