Characterizing pen strokes produced using various commercially available thermochromic inks

The characteristics of commercially available thermochromic ink pens have been studied and described since their appearance in 2006. The wide variety of brands and models now available warrants further study using an expanded sample size, to differentiate the general characteristics from specific characteristics. Herein, the ink strokes of 15 pens purchased in the province of Córdoba, Argentina were studied. First, the initial unaltered strokes were examined. Second, heat-manipulated strokes (with and without friction) were evaluated. Several characterization techniques were employed, such as observation by the naked eye, optical magnification, and light irradiation using different spectral bands. In 100% of the unaltered strokes, the general characteristics of thermochromic inks, such as ink accumulation at the end of the stroke path and a "pasty appearance", were found. It was possible to visualize colourless strokes (i.e. erased strokes) based on their contrast with the paper by shining oblique light at an opposite angle to that of the observation. In addition, the responses to ultraviolet (UV) (365 and 254 nm) and cyan light (505 nm) by infrared techniques were useful for distinguishing the thermochromic ink. Specific characteristics, such as high relief in areas of ink accumulation, less ink accumulation in the internal zone of the stroke, and intensity differences in infrared radiation (IR) luminescence emitted by different brands and models, could be useful in determining the writing tool that was used.

Thermochromic ink disappears with heat but is reversible with cold.UV techniques and IR photography serve to make thermochromic ink visible.Initially use oblique white light opposite to the angle of observation to make strokes visible.