Use ethyl alcohol, water and sodium hydroxide solution to make the basic solution for disappearing ink. Add thymolphthalein to the basic solution to make blue ink or phenolphthalein for red ink. This water-based ink is an acid-base indicator that changes from a colored solution to a colorless one upon exposure to air.
- Make the ink
Add 0.10 grams of thymolphthalein to 10 milliliters of ethyl alcohol to make blue ink. Use 0.10 grams of phenolphthalein, instead of thymolphthalein, to make red ink. Allow it to dissolve in the alcohol. Add 90 milliliters of water to the solution. Then add 20 drops of 3M sodium hydroxide solution, one drop at a time, until the solution turns either dark blue or red.
- Test the ink
Apply the ink to cotton fabric. Upon exposure to air, the ink stain on the fabric disappears in a few seconds. Make the color vanish quickly by holding a cotton ball dampened with vinegar against the ink stain. The white residue on the fabric can be rinsed out with water.
- Make the color reappear
Dampen a cotton ball with ammonia. Brush the location of the ink stain with the cotton ball. This makes the color reappear. Store leftover ink in a sealed container. Dispose of leftover materials by pouring them down the drain.