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How to Make Disappearing Ink

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Disappearing Ink Chemistry
Disappearing ink makes a stain when wet, yet vanishes when the ink dries.

Disappearing ink makes a stain when wet, yet vanishes when the ink dries.

Southern Stock, Getty Images
Disappearing ink is a water-based acid-base indicator (pH indicator) that changes from a colored to a colorless solution upon exposure to air. The most common pH indicators for the ink are thymolphthalein (blue) or phenolphthalein (red or pink). The indicators are mixed into a basic solution that becomes more acidic upon exposure to air, causing the color change. Note that in addition to disappearing ink, you could use different indicators to make color-change inks, too.

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