An alkaline solution of thymolphthalein in alcohol makes a very good disappearing ink. The solution starts out blue, but when it absorbs carbon dioxide from the air, carbonic acid is formed, neutralizing the alkaline solution and causing the blue color to vanish. The color returns when the ink spot is treated with an alkaline solution.
Learn more about this molecule from CAS, the most authoritative and comprehensive source for chemical information.
Stay Ahead of the Chemistry Curve
Learn how ACS can help you stay ahead in the world of chemistry.