Nov. 19, 2003

Iron Ink

What was one of the earliest kinds of ink? Make a very black ink from a chemical reaction between a dietary supplement and tea. This kind of ink was very popular in the eighteenth and nineteenth centuries.

Materials and Equipment:

• 3 or 4 iron-sulfate tablets (sold in drugstores, inexpensively, as ferrous sulfate, for iron-deficiency anemia)
• hot water
• funnel
• cone coffee filter paper or paper towel
• small jars with covers
• a tea bag
• a dip pen (for calligraphy writing) or a small brush

Method of Investigation:

Caution: Don't drink this ink.

1. Prepare an iron-sulfate solution. If the iron-sulfate tablets have a colored coating, put them in water and stir until the coating comes off. Rinse until they're clean and let dry. Crush the tablets into a fine powder. Add about 2 teaspoons of hot water and stir. The iron sulfate will dissolve, leaving a chalky deposit of starch that is used to make the tablets. Pour the solution through a funnel lined with a coffee filter or a folded paper towel. Collect the liquid iron-sulfate solution, which is clear and colorless. Wait a few minutes and the chalky deposit will settle to the bottom. You can easily pour off the clear iron-sulfate solution.
2. Prepare the strongest tea you can make by putting 1/4 cup hot water in a jar with a tea bag. Let it steep for about ten minutes before removing the tea bag.
3. Mix the two solutions together.

Observations & Suggestions:

Ta da! The reaction is immediate. The mixture turns inky as tiny black particles, called a precipitate, form. The precipitate is called iron tannate. Iron tannate darkens when it is exposed to oxygen. Add a little honey to the ink to thicken it before you write with it.

You can try making ink using different sources of tannic acid and iron. See if you can make it from metallic iron. Pour strong tea over steel wool (using the kind from the hardware store that doesn't have soap in it). Let the mixture stand overnight before you try to write with it. If it looks rusty, you've got iron oxide, instead of iron tannate. Add a little vinegar to keep rust from forming.

There was a recipe in a very old book for an ink made by boiling iron sulfate, tea, and pomegranate peels together. If you think this might work, try it and see.

Reprinted with permission from See for Yourself: More Than 100 Experiments for Science Fairs and Projects by Vicki Cobb. Text © 2001 by Vicki Cobb (www.vickicobb.com). Published by Scholastic Reference.

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