A marking instrument includes a body formed with a first end and a second end and sealed at the second end to define a fluid reservoir. The marking instrument includes a tip assembly positioned at the first end having a rigid nib with a fluid path formed longitudinally therethrough. The rigid nib has a first end forming a first spreader surface and a second end adjacent to the fluid reservoir and cooperates with a shiftable valve positioned within the fluid path. The shiftable valve includes a valve actuator having a contact surface position substantially adjacent to the first spreader surface. The tip assembly may further include an adjustable nib having a second spreader surface adapted to be positioned adjacent the first spreader surface to form a composite spreader surface.