Watercolor painting involves the mixture of pigment, water, and an adhesive agent, typically applied to paper but sometimes silk or vellum. Variations on this practice have existed around the world, with early instances including ancient Egyptian papyrus painting, ancient Chinese silk painting, and medieval manuscripts. Greater standardization in watercolor production was furthered by the wide distribution of a list of usable pigments in 17th-century England and the invention of portable watercolor boxes in the early 18th century. Old Masters like Albrecht Dürer and Sir Anthony Van Dyck used the medium primarily for landscapes, though often as a delicate accent in ink and chalk drawings. Watercolor gained its strongest standing in the United Kingdom, with watercolorists gaining admission to the Royal Academy by the end of the 18th century and J. M. W. Turner adopting it as a preferred medium. While less admired in continental Europe, the signature Impressionist styles of Paul Cézanne and Camille Pissarro were both greatly indebted to the medium. In the 20th century, watercolor was widely used by the Fauvists and early abstractionists like Wassily Kandinsky and Paul Klee, and then later in figurative painting by the likes of David Hockney and Francesco Clemente.