Visualizing Indented Writing on Thermal Paper by the Controlled Application of Heat
Indented writing on thermal paper made with either one, two, or three sheets of paper above the thermal paper has been visualized by the controlled application of heat to the thermal paper at temperatures below the paper's normal color change temperature. Indentations created by applying a variable pressure to a steel letter stamp showed that, with one sheet above the thermal paper, indentations were more visible at lower pressures than with either two or three sheets above. Handwriting from 20 volunteers produced indented writing graded with most of the text clear and easy to read for all samples with one sheet above, half the samples with two sheets above and eight samples with three sheets above. Comparison with ESDA showed that, with three sheets above, there was a statistically significant difference (p < 0.01), with heating producing more samples than ESDA with most of the text clear and easy to read.