Derwent Inktense Pencil, Mustard. This innovative, water-soluble ink stick pencil can be mixed with water to create colorful, fluid, ink-like effects. Once dry they will resemble Sumi ink brilliance, will not dissolve, and other media can be applied over the color to achieve the desired effect. Layer colors, experiment with mixed media and create vibrant works of art. This line also offers an insoluble outliner pencil to define border limits to drawings and to keep colors from bleeding together.