Fading Time Study on Prepared Thymolphthalein, Phenolphthalein and their Mixture Disappearing Ink

Disappearing ink was prepared using different concentrations of thymolphthalein, phenolphthalein and their mixture, applying to different types of handwriting surfaces such as cotton, polyester and polyamide. The effects of thymolphthalein, phenolphthalein and alkali concentrations (i.e. pH) on the fading time were studied. The handwriting stability increased when the concentration of thymolphthalein or phenolphthalein was increased. At a high concentration of alkali with phenolphthalein and its mixture with thymolphthalein, the handwriting stability decreased with polyester or polyamide handwriting surfaces and the stability increased in the case of cotton. When the faded handwriting surfaces were subject to the thermal effect in a thermostatically controlled oven at 100°C for 10 minutes by hanging them with suitable hooks, there was no change in the faded handwriting. When they were at 150°C for 20 minutes, the faded phenolphthalein ink, which contained 0.5ml of 1N NaOH, was visible and shown red on the polyester and polyamide handwriting surfaces, but there was no change on the faded cotton handwriting surface.