Ecoline Duotip pens contain concentrated, transparent watercolor paint. These 6ct brilliant watercolors in combination with the two different tips give you the freedom to make fine, or broad lines and to color larger areas. The dye-based Duotips work perfectly in combination with the Ecoline brush pen and Ecoline bottles and offer you a wide range of options in line weights. styles and color variations. Mix with water for beautiful watercolor effects and smooth color transitions.