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How to Make Disappearing Ink

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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.

How Disappearing Ink Works

When the ink is sprayed onto a porous material the water in the ink reacts with carbon dioxide in the air to form carbonic acid. The carbonic acid then reacts with the sodium hydroxide in a neutralization reaction to form sodium carbonate. Neutralization of the base causes a color change of the indicator and the stain disappears:

Carbon dioxide in the air reacts with water to form carbonic acid:

Disappearing Ink Materials

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Here’s what you need in order to make your own blue or red disappearing ink:

Make Disappearing Ink

Here’s how to make your own disappearing ink:

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