Use this tool to wash your drawings or add color.
Fill the tool with water, press it onto the back of your pen, and wash your line drawings or add another color.
You can use any liquid that flows freely, water, ink wash, or watercolor.
You can now draw using the nib, then spin the pen in your hand half a turn to wash your drawing with water, dilute ink solution or a touch of watercolor. This is a great way to add shading and tonal value, which gives more depth and character. Laying down the ink line is the first step, but washing the line adds subtlety that's not possible to get through a flex nib alone.
You can purchase additional brushes. They are easy to replace, just pull out the old brush with the ferrule, press in the new brush with ferrule, and off you go.