Tombow - Dual Brush Marker - Open Stock - N00 Colorless Blender. TOMBOW-Dual Brush Pen Open Stock. This dual brush pen has a versatile and flexible nylon fiber brush tip on one end that creates medium or bold strokes by simply changing brush pressure. The fine tip on the other end is for smooth straight lines or writing. The water based ink is blendable, odorless and non-bleeding. Acid free and non-toxic. Imported.