Kyffin Williams (1918–2006) was a Welsh artist who mostly painted with a knife. Slatherings of oil paint, using a limited palette of muted colours and black outlines. His paintings range from minimalist and quite abstract to landscapes full of suggested detail as well as portraits. My favourites are his sheepdogs and seascapes, plus his stone walls.
There’s a BBC documentary (“The Man Who Painted Wales”) on Kyffin Williams; if you look on YouTube you might find more clips.