A retractable ink pen including an elongate ink cartridge having a writing end and an exposed ink opening, wherein the writing end moves from a retracted position to an extended position for writing. The retractable ink pen includes a cap including a recess with an inner surface having one of: i) a position structure, and ii) both a first locator and a second locator spaced a distance from the first locator along a first longitudinal axis. The retractable ink pen further includes an elongate barrel including an outer surface having the other of the position structure and both the first locator and the second locator, wherein the position structure is located at the first locator when the writing end is in the retracted position and wherein the locating structure is located at the second locator when the writing end is in the extended position.

A writing instrument that includes a barrel extending along a longitudinal axis (A) and a tip mounted at the front of the barrel, further including a protective sleeve for the tip, the sleeve being mounted coaxially on the barrel and movable relative to the barrel between a protective position where it covers the tip and a retracted position where it exposes the tip to allow writing. The sleeve includes an inner wall which includes a helical cam engaging with a guide element formed on the barrel so that the sleeve is movable in translation combined with rotation.

A writing instrument that includes a barrel extending along a longitudinal axis (A) and a tip mounted at the front of the barrel, further including a protective sleeve for the tip, the sleeve being mounted coaxially on the barrel and movable relative to the barrel between a protective position where it covers the tip and a retracted position where it exposes the tip to allow writing. The sleeve includes an inner wall which includes a helical cam engaging with a guide element formed on the barrel so that the sleeve is movable in translation combined with rotation.

A non-sealing fluid-based writing instrument includes a body, a fluid reservoir, and a writing tip. The writing tip is fluidly connected to the fluid reservoir and configured to dispense fluid contained in the fluid reservoir on a surface when in use. The writing tip is concealed when the writing instrument is in a retracted position. The writing tip is exposed when the writing instrument is in an exposed position. The writing instrument is non-sealing. In both the retracted and exposed positions, the writing tip is exposed to the atmosphere or an exterior of the body of the writing instrument. A writing fluid for use in the non-sealing fluid-based writing instrument that includes one or more polyglycols. The polyglycol serves as a humectant that prevents the writing fluid from drying even when exposed to atmosphere for prolonged periods of time.

A non-sealing fluid-based writing instrument includes a body, a fluid reservoir, and a writing tip. The writing tip is fluidly connected to the fluid reservoir and configured to dispense fluid contained in the fluid reservoir on a surface when in use. The writing tip is concealed when the writing instrument is in a retracted position. The writing tip is exposed when the writing instrument is in an exposed position. The writing instrument is non-sealing. In both the retracted and exposed positions, the writing tip is exposed to the atmosphere or an exterior of the body of the writing instrument. A writing fluid for use in the non-sealing fluid-based writing instrument that includes one or more polyglycols. The polyglycol serves as a humectant that prevents the writing fluid from drying even when exposed to atmosphere for prolonged periods of time.