Invisible ink and secret messages seem to belong exclusively to the world of spy stories and schools of magic, yet anyone can make a fluid with magical powers by combining simple ingredients of everyday use. During the American Revolutionary War, soldiers sent invisible secret messages written with lemon juice. In the First World War, a mixture of water and pulverized aspirin was used. In extreme cases, the soldiers even used their own sweat or saliva to write hidden messages. You don't need cutting-edge technology to create invisible ink, and you can do it today. Using ordinary baking soda and a light bulb, you can write and reveal hidden messages just like a legendary spy or a talented soldier.
Steps
Part 1 of 4: Writing a Secret Message with Bicarbonate
Step 1. Mix water and baking soda
To make a magical ink, the two ingredients must be in similar quantities. To get the best possible result, you will need to incorporate as much baking soda as possible into a small bowl of water. Add only a little at a time and mix slowly to completely saturate the water.
- 60 ml of water is able to dissolve 3 tablespoons of bicarbonate.
- If there are bicarbonate deposits in your "ink" that are impossible to dissolve, it means that the solution is oversaturated. In this case, do the opposite: add a little water at a time until the residual bicarbonate dissolves completely.
Step 2. Dip a small brush or cotton swab into the solution
Treat the baking soda mixture as you would ordinary ink or watercolor, and only take a little at a time.
Step 3. Write your message on a blank piece of paper
Using the brush or cotton swab, write the secret text in block capitals on an ordinary piece of paper. Make sure the letters are clear and large enough to be legible. The water will spread into the paper, distorting the lettering, so you may need to practice to be able to write legibly using the brush or cotton swab.
- Consider writing a coded message for added security. For example, a simple substitution code swaps each letter of the alphabet for another or a number following a predetermined pattern.
- A plain white sheet of lined paper is an excellent surface for writing your messages.
Step 4. Let the invisible ink dry
You must make sure that the message dries up and does not notice that the card has been manipulated. To achieve a perfect result, follow these instructions:
- Press the sheet of paper between two books or two heavy objects. Place a few more sheets of paper above and below the one you wrote the message on to prevent excess water from ruining the books you used as a weight.
- Hang up the paper with the message. The reason photographers hang their prints to dry is that the force of gravity helps to keep the paper from curling. You can use the same method by hanging your paper with clothes pegs.
- By using thick, high-quality paper or card stock, you are less likely to sag when wiping.
Step 5. Consider using steam
When you write your message on the paper, the aqueous ink will warp the paper, leaving marks that will remain visible even after it dries. By briefly exposing the paper to the steam, you will be able to hide the fact that it has been manipulated, increasing the chances that your message will not be detected. There are two methods of steaming the sheet properly:
- Boil the water in the kettle or saucepan and hold the foil near the escaping steam. Remember that the steam reaches a very high temperature (even higher than that of boiling water), so use a pair of kitchen tongs or similar utensil to hold the paper.
- Use the steam boost of the iron, setting it to the minimum amount. Keep your fingers away from the steam and lightly iron the sheet.
- If you have decided to use steam, it is essential to dry the sheet using one of the methods described above.
Step 6. Consider adding a deceptive message to the dry paper using a pen or pencil
If your ticket is intercepted before you can send it, a blank page could arouse suspicion. After all, who would ever bother to deliver a blank sheet of paper? By adding a deceptive message, you can sidetrack enemies. For instance:
- Writing a fake shopping list on top of the secret text is a classic spy trick. Who would suspect a simple list of things to buy.
- If you intend to reveal your secret message with a liquid (grape juice or red cabbage), don't use the pen to write the deceptive message! Otherwise the ink from the pen will spread across the page when you apply the telltale fluid.
Part 2 of 4: Revealing the Secret Message with Heat
Step 1. Expose your message to a heat source
It takes quite a bit of heat to oxidize the carbon contained in the baking soda, thus revealing the hidden text. For this reason you will need to use a safe, yet powerful, direct heat source. There are several commonly used items that can be right for you. For instance:
- Incandescent light bulb - you will need to hold the foil next to a boiling light bulb for several minutes to heat the baking soda as needed.
- Electric cooker - be careful not to bring the paper too close to the hot coils to avoid the risk of starting a fire.
- Hair dryer - turn it on to the hottest temperature possible and direct the jet of air on the sheet to oxidize the carbon.
- Iron - to reveal the secret message, you need to turn off the steam. Slowly iron the entire surface of the sheet.
- Oven - you can place the card in a pan and place it in the oven at 250 ° C, checking every few minutes if the letters have appeared.
- Heater or toaster - keep an eye on the sheet to reduce the risk of fire.
Step 2. Be careful to prevent your sheet of paper from catching fire
The paper is flammable and keeping the ticket close to direct heat means that it can catch fire. Choose the method that makes you feel safest and possibly avoid using open flames.
- Halogen bulbs give off more heat than incandescent bulbs, so the risk of fire increases.
- The electric stove heats up slowly, but then becomes very hot. Hold the sheet with kitchen tongs and do not get too close to the coils.
Step 3. Slowly heat the paper that holds your secret message
Whichever method you have chosen to reveal the presence of invisible ink, it is important to proceed slowly so as not to risk heating it more than necessary.
- Move the sheet over the heat source to prevent a single part from overheating.
- It may take several minutes for the letters to appear hidden, depending on the degree of heat used, the thickness and texture of the paper, and the saturation level of your invisible ink.
Step 4. Read the brown letters that make up the message
When the paper heats up, the text will appear and it will appear that it has been burned on the paper. The characters will be a brown hue because the carbon in the bicarbonate will have oxidized faster than normal due to the heat.
The oxidation process is the same as that which causes the flesh of an apple to turn black after cutting it
Part 3 of 4: Revealing the Invisible Ink with Grape Juice
Step 1. Pour the grape juice into a bowl
The most suitable for making invisible ink appear is concentrated ink (sometimes it is also possible to find it frozen). Concentrated grape juice has a higher acidity, so it will produce a more intense reaction when it comes into contact with the bicarbonate contained in the ink.
In fact, you can use any dark, acidic liquid, such as cherry or blackcurrant juice or common balsamic vinegar
Step 2. Tap or swipe concentrated grape juice onto the sheet with the hidden message
Dip a sponge or brush in the telltale fluid and wipe the page to make the magic ink appear.
- Be careful when using concentrated grape juice as it stains.
- Don't use the same brush or cotton swab you wrote the message with.
Step 3. Read the gray letters that make up the secret message
When you pass the grape juice on the paper, the characters will appear as if by magic in front of your eyes. They will have a greyish color given by the chemical reaction produced by the meeting between bicarbonate, which is a basic element, and grape juice, which is an acid element.
Part 4 of 4: Revealing the Invisible Ink with Red Cabbage Extract
Step 1. Heat half a liter of water
You can use the stove, kettle or microwave. The water does not have to boil, but it is important that it is very hot to function properly.
Step 2. Dip a few red cabbage leaves in boiling water
For convenience, you can put 10-15 red cabbage leaves in a large bowl and pour hot water over it. Leave them to soak for a full hour while the water cools. The pigment in the cabbage should gradually dye it.
To get a good result, all the cabbage leaves must be completely submerged in water
Step 3. Drain the cabbage leaves
When the water has cooled, remove the leaves using kitchen tongs or a colander.
Store your telltale fluid in the freezer. Simply keeping it in the refrigerator will spoil and become foul smelling
Step 4. Dab or wipe the red cabbage extract on the paper
Dip a sponge or brush into the tell-tale fluid and smoothly swipe the page to make the ink appear invisible.
Step 5. Read the bluish letters that make up the message
When you pass the cabbage extract on the paper, the characters will appear as if by magic in front of your eyes. They will have a bluish color because the red cabbage extract will act as a pH indicator and will detect baking soda.
If the message was written with lemon juice, which is an acid, the characters will have a pinkish color rather than leaning towards blue or green
Advice
- Make sure the invisible ink isn't too watery. For the best possible result, keep adding bicarbonate until the solution is completely saturated.
- If you can't find concentrated grape juice, you can use regular grape juice, but in that case the characters will be less visible.
Warnings
- Be careful not to use too much water when creating invisible ink. Otherwise it could soak the paper and the characters could smear.
- If you intend to make the message appear using heat, be careful not to overheat the paper. Remember that halogen bulbs give off more heat than incandescent bulbs, so the foil could catch fire. The same could happen if you hold the paper too close to the electric stove.
- If the red cabbage extract goes bad, it will give off a pestilential smell. If you want to keep it for decoding other messages, pour it into the ice cube mold (or other freezer-safe container) and freeze it.
