A Review on Porous-Tipped Writing Instruments—Current Market Trends, Properties, and Analytical Methodologies

Porous-tipped pens, commonly referred to as “felt-” or “fiber-tipped” pens, are a ubiquitous form of writing instruments that can have artistic, non-artistic, and even mixed applications depending both on the product’s intended use and the user’s preference. Despite a few studies that have been carried out to gather information about the physical and chemical properties of these writing instruments, poroustipped pens and their inks constitute an under-researched area within the field of forensic document examination. The present review aims to thoroughly discuss the developments of the porous-tipped pen throughout history, the criteria that help differentiate stroke features between porous-tipped pens and other fluid pen inks, and any information gathered about their properties. A survey of the current trends of the porous-tipped pen market, the key findings from said survey, and artistic blending writing instruments are also discussed. The survey includes specifications from 141 different brands and 966 individual products from 2018 to 2019. Finally, the current state of porous-tipped pens within questioned documents is discussed. The review of existing porous-tipped pen studies and the findings of the present open-source survey allowed to highlight a number of challenges that the forensic document examiner has to face when asked to characterize and compare graphical, physical, and chemical features left by porous-tipped pens on a questioned specimen. These challenges may stem from the increased number of these writing instruments on the market, the increase of complexity of ink formulations (i.e., blending capabilities of some artistic pens), the difficulty to distinguish between artistic and nonartistic markers due to a larger availability of the former to the general public in the last years, and the diversity of porous-tipped pen tip types.