A variation is to make disappearing ink. The 'ink' is a pH indicator that becomes colorless upon reacting with air. You can make the color reappear by applying a basic solution.
Make Invisible Ink
Making invisible ink to write and reveal secret message is a great science project to try if you think you don't have any chemicals. Why? Because just about any chemical can be used as invisible ink if you know how to use it!
What Is Invisible Ink?
Invisible ink is any substance that you can use to write a message that is invisible until the ink is revealed. You use the ink by writing your message with it using a cotton swab, dampened finger, fountain pen, or toothpick. Let the message dry. You may want to write a normal message on the paper so that it doesn't appear to be blank and meaningless. If you write a cover message, use a ballpoint pen, pencil, or crayon, since fountain pen ink could run into your invisible ink. Avoid using lined paper to write your invisible message, for the same reason.
How you reveal the message depends on the ink you used. Most invisible inks are made visible by heating the paper. Ironing the paper or holding it over a 100-watt bulb are easy ways to reveal these types of messages. Some messages are developed by spraying or wiping the paper with a second chemical. Other messages are revealed by shining an ultraviolet light on the paper.
Make Invisible Ink
Anyone can write an invisible message, assuming you have paper, because body fluids can be used as invisible ink. If you don't feel like collecting urine, here are some alternatives:
Heat-Activated Invisible Inks
Iron the paper, set it on a radiator, place it in an oven (set lower than 450° F), hold it up to a hot light bulb.
Iron the paper, set it on a radiator, place it in an oven (set lower than 450° F), hold it up to a hot light bulb.
- any acidic fruit juice (e.g., lemon, apple, or orange juice)
- onion juice
- baking soda (sodium bicarbonate)
- vinegar
- white wine
- dilute cola
- diluted honey
- milk
- soapy water
- sucrose (table sugar) solution
- urine
Inks Developed by Chemical Reactions
These inks are sneakier, because you have to know how to reveal them. Most of them work
These inks are sneakier, because you have to know how to reveal them. Most of them work
using pH indicators, so when it doubt, paint or spray a suspected message with a base (like sodium carbonate solution) or an acid (like lemon juice ). Some of these inks will reveal their message when heated (e.g., vinegar).
- phenolphthalein (pH indicator), developed by ammonia fumes or sodium carbonate (or another base)
- thymolphthalein, developed by ammonia fumes or sodium carbonate (or another base)
- vinegar or dilute acetic acid, developed by red cabbage water
- ammonia, developed by red cabbage water
- sodium bicarbonate (baking soda), developed by grape juice
- sodium chloride (table salt), developed by silver nitrate
- copper sulfate, developed by sodium iodide, sodium carbonate, potassium ferricyanide, or ammonium hydroxide
- lead(II) nitrate, developed by sodium iodide
- iron sulfate, developed by sodium carbonate, sodium sulfide, or potassium ferricyanide
- cobalt chloride, developed by potassium ferricyanide
- starch (e.g., corn starch or potato starch), developed by iodine solution
- lemon juice, developed by iodine solution
Inks Developed by Ultraviolet Light (Black Light)
Most of the inks that become visible when you shine a black light on them also would become visible if you heated the paper. Glow-in-the-dark stuff is still cool. Here are some chemicals to try:
Most of the inks that become visible when you shine a black light on them also would become visible if you heated the paper. Glow-in-the-dark stuff is still cool. Here are some chemicals to try:
- dilute laundry detergent (the bluing agent glows)
- body fluids
- tonic water (quinine glows)
- vitamin B-12 dissolved in vinegar
Any chemical that weakens the structure of paper can be used as an invisible ink, so you might find it fun to discover other inks around your home or lab.
Make Disappearing Ink
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. Neutralizaton 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:
CO2 + H2O → H2CO3
The neutralization reaction is sodium hydroxide + carbonic acid -> sodium carbonate + water:
2 Na(OH) + H2CO3 → Na2CO3 + 2 H2O
Disappearing Ink Materials
Here's what you need in order to make your own blue or red disappearing ink:
- 0.10 g thymolphthalein for blue ink or phenolphthalein for red ink (1/3 of 1/8 tsp)
- 10 ml (2 tsp) ethyl alcohol (ethanol) [can substitute 14 ml or 3 tsp of ethyl rubbing alcohol]
- 90 ml water
- 20 drops of 3M sodium hydroxide solution or 10 drops 6M sodium hydroxide solution [make a 3 M sodium hydroxide solution by dissolving 12 g of sodium hydroxide NaOH (1 level tablespoon of lye) in 100 ml (1/2 cup) of water.]
Make Disappearing Ink
Here's how to make your own disappearing ink:
- 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 Materialssection).
- 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.
SOURCE: www.about.com/education By: Anne Marie Helmenstine, Ph.D. ( Chemistry Expert )
