- Dissolve the thymolphthalein (or phenolphthalein) in the ethyl alcohol.
- Stir in 90 ml of water (will produce a milky solution).
- Add sodium hydroxide solution dropwise until the solution turns a dark blue or red (might take slightly more or less than the number of drops stated in the Materials section).
- Test the ink by applying it to fabric (cotton tee-shirt material or a table cloth works well). Paper allows less interaction with air, so the color change reaction takes more time.
- In a few seconds, the 'stain' will disappear. The pH of the ink solution is 10-11, but after exposure to air will drop to 5-6. The damp spot will eventually dry. A white residue may be visible on dark fabrics. The residue will rinse out in the wash.
- If you brush over the spot with a cotton ball that has been dampened in ammonia the color will return. Similarly, the color will vanish more quickly if you apply a cotton ball dampened with vinegar or if you blow on the spot to improve air circulation.
- Leftover ink may be stored in a sealed container. All of the materials may be safely poured down the drain.
Disappearing Ink Safety
- Never spray disappearing ink into a person's face. Particularly avoid getting the solution in the eyes.
- Preparing/handling the sodium hydroxide (lye) solution requires adult supervision, as the base is caustic. In case of skin contact, immediately rinse well with water.