Affiliation: | 1. https://orcid.org/0000-0003-1691-6171;2. Department of Medicine, Institute of Forensic Sciences, Istanbul University‐Cerrahpasa, Cerrahpasa, Istanbul, 34098 TurkeyCorresponding author: Faruk Asicioglu, M.D., Ph.D. E‐mail:;3. Department of Science, Institute of Forensic Sciences, Istanbul University‐Cerrahpasa, Cerrahpasa, Istanbul, 34098 Turkey;4. Department of Chemistry, Faculty of Science and Letters, Istanbul Technical University, Maslak, Istanbul, 34469 Turkey;5. Department of Medicine, Institute of Forensic Sciences, Istanbul University‐Cerrahpasa, Cerrahpasa, Istanbul, 34098 Turkey;6. Forensic Science Consultants, Inc., 433 Airport Boulevard, Suite 406, Burlingame, CA, 94010‐2017 |
Abstract: | Disappearing inks can be used for forgeries in many fields. In this study, thymolphthalein indicator solution was prepared as a disappearing ink. A total of 54 different solutions containing thymolphthalein were prepared at six different concentrations and nine different pH values. Among the prepared solutions, 0.16 g/50 mL and 0.32 g/65 mL thymolphthalein at pH 14 were the optimum solutions that were not distinguishable from regular ink when applied to promissory note. Fountain pens were filled with the abovementioned ink solutions and applied to promissory notes for experimental purposes. After 40 h, ink residues were not visible on promissory notes written with the ink with the optimum pH (pH = 14) value. To decipher the entries that disappeared, an instrumental method (Video Spectral Comparator‐8000) and a chemical method (using NH3 vapor) were used, succeeded at 0.32 g/65 mL, but failed at 0.16 g/50 mL thymolphthalein. Therefore, NH3 had to be sprayed for 0.16 g/50 mL with negligible harm. |