From Wikipedia:

Early on, Wyeth became interested in oil, his grandfather's primary medium, although he is also adept in watercolor and tempera, his father's preferred media. In describing his aunt's way of thickly applying oil to her palette, he stated, "I could eat it. Tempera never looked particularly edible. You have to love a medium to work in it. I love the feel and smell of oil."[1][2] In addition to studying his aunt's oil technique, he also admired his father’s and grandfather's work, and that of Howard Pyle, his grandfather’s teacher, as well as American masters Winslow Homer and Thomas Eakins. What inspired Wyeth most was not the subject matter or technique of his grandfather, but his "sense of total personal involvement with and intuitive grasp of his subjects". Jamie Wyeth adopted a wider palette of colors than his father’s and closer to his aunt’s and grandfather's.[1] Wyeth's artistic reach is broader than his father's and grandfather's. He excels in drawing, lithography, etching, egg tempera, watercolor, and mixed media.[2][10] Though grounded in this family’s artist tradition and subjects, and bound by the same solitude of his art, his wider travels and experiences have shaped a more rounded artist. In travels to Europe, he studied the Flemish and Dutch masters, and learned the intricate and exacting process of lithography, producing a substantial amount of graphic work.[10] On portrait painting, Wyeth stated, "To me, a portrait is not so much the actual painting, but just spending the time with the person, traveling with him, watching him eat, watching him sleep. When I work on a portrait, it's really osmosis. I try to become the person I'm painting. A successful portrait isn't about the sitter's physical characteristics—his nose, eyeballs and whatnot—but more the mood and the overall effect. I try not to impose anything of mine on him. I try to get to the point where if the sitter painted, he'd paint a portrait just the way I'm doing it."[11] Like his aunt Carolyn, Wyeth enjoys painting animals, such as chickens and dogs. To do so, he pays particular attention to the texture of the animals fur or feathers, the glossiness of its eye, the grass around its feet. To create the desired effects, he used brushstrokes for texture and varnish for sheen.[2]