Abstract

Background: Secret writing, or invisible writing, involves concealing messages so they remain unseen until revealed by specific techniques. It has been practiced since ancient times using both physical and chemical methods to ensure message confidentiality. Over time, secret communication evolved from early cipher tools such as the Spartan scytale to modern chemical-based invisible inks.Aim: The study aims to examine and compare forensic methods used to detect and decipher secret writings made with biological fluids, chemical substances, and fruit or vegetable juices on different types of paper substrates. Materials and Methods: A total of 180 samples were prepared using various invisible inks on three types of paper: bond paper, drawing paper, and A4 sheets. Each sample was developed using three principal visualization techniques heat exposure, ultraviolet (UV) illumination, and iodine fuming to reveal and compare the visibility of the concealed writings. Results: The experimental results showed that heat exposure and iodine fuming were more effective and sensitive than UV illumination in visualizing invisible inks, particularly those prepared from fruit juices and chemical reagents. The clarity and longevity of the developed writings varied with the type of ink, paper, and developing method used.Conclusion: Traditional development techniques like heat and iodine fuming remain highly reliable for detecting invisible writings when compared with UV illumination. Combining these conventional approaches with modern forensic techniques can significantly improve the accuracy and efficiency of detecting concealed messages

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