Abstract: 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.

Abstract: A mechanism for a writing implement prevents back flow of writing fluid from a writing tip back to a fluid reservoir of the implement. The mechanism has a valve chamber with a proximal end and a distal end. The mechanism also has a valve seat disposed at the distal end of the valve chamber. A first fluid passage in the writing implement defines a first opening into the valve chamber at the valve seat. The first fluid passage is in fluid communication with both the fluid reservoir and the valve chamber. A valve body has a body diameter and is loosely held within the valve chamber. The valve body prevents fluid back flow from the valve chamber to the first fluid passage when borne against the valve seat. A second fluid passage in the writing implement is in fluid communication with both the writing tip and the valve chamber. The second fluid passage has a second opening disposed at the proximal end of the valve chamber.