These trials were preliminaries to the illustrations for "The Cats In Krasinski Square", a picture book written by Karen Hesse. Such trials can be tedious and time-consuming (if for example one needs to let them dry overnight) but they are always worth the time and trouble. And they are just as valuable whether one is working with hand tools or on the computer. Much better than finding out mid-illustration or mid-book that one's media are not up to the task.
And sometimes---if the media insist on behaving capriciously, or one is unable to find any media that satisfy one's inner vision---these trials can in fact become "that other kind of trial". Such is the life of the conscientious illustrator.