Zig Medium Watercolor Brush Water color system brush2o range is perfect for any artist who wishes to paint anywhere at anytime All you need to do is fill the barrel with water and away you go Works perfectly with other zig water-based markers, so for any artist on location this is the cleanest and easiest way to paint Water color system brush2o pens have a retractable valve Have complete control of how much water you release by gently squeezing the barrel