Invisible ink is special compounds that, when applied to a sheet of paper, at home do not leave marks on the surface of the document. To create them, various components are used or ready-made equipment is purchased. If certain conditions are met, the hidden text appears.
This involves treatment with reagents or changing the temperature. Often, such ink becomes visible when heated. Initially, this method was used for secret correspondence. Today, it is considered a kind of shorthand.
Invisible ink first appeared in the 1st century AD. The recipe was based on the juice of gall nuts, which was attested in the works of Philo of Alexandria. To reveal hidden information, they used a composition of iron-copper salt.
Another means for these purposes was suggested by Ovid, who wrote the text on a paper surface using milk. Then he revealed the message by heating the paper sheet, which contained secret information. Pliny the Elder used plant juice to display a hidden message.
Materials
To write a secret message, special substances are used that do not leave traces on a sheet of paper when interacting with it, but under certain conditions have the property of manifestation and become visible. The property is mainly realized when in contact with high temperatures, chemicals or lighting.
To make a note, a secret inscription is initially made on a piece of paper using invisible ink. Afterwards, information that is not important for either the sender or the recipient is written on top of the first message. You can make invisible ink at home with your children, using any components and options.
There are several ways to create a product:
- cobalt;
- onion, apple juice;
- milk;
- washing powder;
- baking soda;
- lemon juice.
Inks made from such components are considered neutral because they do not chemically affect the paper sheet during the development of the hidden text. They only color it with decomposition products. The organic substances that are part of their composition begin to decompose during heating with the appearance of products colored in a yellowish or light brown shade.
In addition to invisible ink that was created industrially, there are also compounds that glow under an ultraviolet lamp and pens that contain ultraviolet ink. The contents of the pen will be discolored under the influence of an increase in temperature to + 65℃.
There is a simple eraser at the end of the stationery. During friction, the temperature of the paper sheet increases, eventually the text disappears. To hide a large message, it is recommended to use a hot hair dryer, blowing a hot stream of air onto the page. If after erasing the text, the paper sheet is kept in the freezer compartment for 24 hours, it will become visible.
You can buy a "spy pen" at a stationery store that leaves marks that show up when exposed to ultraviolet light.
Analogues of such a product are anti-counterfeit pigments with paints, which are powder components, with the help of which it is permissible to mark things, securities and banknotes. Daylight will not help to see the powder. To do this, you need to use ultraviolet light, on which it is permissible to see all the grains of powder or paint.
To make fluorescent ink, it is recommended to use a simple washing powder, which contains optical brighteners. If the component is diluted in a minimum volume of liquid, you can write a secret letter. When the solution dries completely, it will not leave marks on the paper. It can only be seen when the ultraviolet lamp is on.
Optical brighteners can be purchased separately. They are often used to whiten fabrics, clothing, and blue-tinted printer paper. The powder can be used to produce sympathetic inks that can be developed on any type of paper.
It is permissible to use alcohol with aspirin tablets to make ink. To do this, dissolve 3 tablets in a small volume of alcohol-containing liquid. If there is sediment at the bottom after dissolution, the solution must be filtered. Then you can proceed to writing the message. However, this method is not suitable for all types of paper. It is not recommended to use it on paper that is suitable for printing on a printer.
To create ink, you can use products that are sold in pharmacies:
- curcumin;
- trypaflavin;
- quinine sulfate.
Sodium fluorescein is suitable for creating ink, but after application, its natural shade will stand out on a light sheet of paper. In this regard, such ink is not invisible. Materials intended for applying sympathetic ink can be any.
The following tools are considered to be in high demand:
- sheet of paper;
- cotton swab;
- tree;
- metal;
- plastic;
- glass surface;
- fabric material.
Some types of ink require a prepared surface. It is recommended to use a hard white sheet of paper or cardboard for writing, because the inscription appears better on them.
Methods of manifestation
To reveal a secret message, various methods are used:
| Manifestation variant | How it works |
| Mechanical | Ultramarine, iodine solution or vapor are used to develop the recording. The paper can be moistened with water or sprinkled with a fine powder of iron oxide, antimony, ochre or graphite. |
| Optic | The method is based on the use of photographs, ultraviolet light from a lamp, infrared rays, penetrating radiation and viewing in visible light. The latter is directed at the sheet at an angle or straight, with the paper placed on a light-technical matting glass. To create a backlight, an incandescent lamp with a matte bulb is placed under the document. If the inscription contains silver nitrate, it begins to darken during translucence, becoming noticeable. Penetrating rays can be placed parallel to the surface, at an angle or directly on the paper sheet. Most types of ink can fluoresce in ultraviolet rays. |
| Thermal | To reveal the text, use a heated object, such as an iron. When exposed to a heated object, try not to deform the sheet. The message, which contains potassium nitrate, appears when touched by an open flame. As a result, the compound begins to decompose. During the procedure, it is imperative to adhere to safety precautions, because some types of acids are capable of decomposing not only the inscription, but also the paper sheet. |
| Chemical | When using this method, the effect of hydrogen sulfide vapors, hydrogen peroxide or ammonia, dipping in a chemical bath or moistening with certain solutions are used. Sometimes special chemical reagents are used when making contact photographs. |
The best homemade sympathetic ink is considered to be from soda, because it is easy to make, it has no smell and is characterized by a long shelf life. At the same time, it dries much faster, is invisible on a sheet of paper and appears brighter.
Master classes
To create cute ink with kids, it is better to use reliable and safe options using common products like lemon juice, baking soda and milk.
From soda
Invisible ink can be made at home in two ways, each of which uses baking soda. It will take no more than 5 minutes to conduct a quick chemical experiment. The procedure can be carried out with children over 8-10 years old.
Before creating ink, you should prepare the necessary materials in advance:
- sheet of paper;
- spoon;
- cotton swab (can be replaced with a toothpick, with cotton wool wound around one end);
- soda;
- a candle (if you don’t have one, you can use a regular table lamp or an iron to reveal the hidden inscription);
- warm water.
Instead of a cotton swab, you can use a fountain pen, which should be filled with the prepared soda liquid before applying the inscription.
After preparing all the ingredients, you can move on to the ink making stage:
- Make a concentrated soda solution by mixing equal amounts of warm water and soda. Mix the mixture thoroughly, you don't have to wait for the loose powder to dissolve completely.
- Dip a cotton swab or toothpick into the prepared solution and write a specific note on the sheet.
- Dry the paper sheet well, since soda ink leaves wet prints. To dry in winter, you can use a heating battery or put the document on a windowsill in direct sunlight if the weather is hot outside.
- When the paper is completely dry, it can be developed. Hold the sheet over a burning candle or a gas stove flame.
The development stage must be controlled because the paper can catch fire if it is held motionless over an open flame. In this regard, it is recommended to move the sheet slowly over the fire. You can also develop the inscription using an iron, which is heated to the minimum temperature. The device should go over the surface of the paper containing the text. Upon completion of the procedure, the inscription should appear in a yellow-brown shade.
The second method of making sympathetic ink involves a similar instruction for creation, but for development, not the heating method is used, but grape juice. This option for creating ink is suitable for classes with small children, who are not recommended to show the procedure of heating a sheet of paper with a burning candle or an open flame of a gas stove.
To reveal the hidden text, you need to go over it with a brush that has been previously soaked in juice. During the interaction of the two components, a chemical reaction begins, which facilitates the manifestation of the inscription, as a result it becomes visible.
Helpful tips when working with soda ink:
- It is not advisable to use halogen bulbs because they can cause the paper to ignite;
- regular grape juice can be replaced with concentrate to make the change in shades more obvious and rich;
- The soda solution can be made weaker by dissolving 1 part of the loose powder in 2 parts of liquid (the end result will remain the same).
From lemon
It is possible to create sympathetic ink at home using freshly squeezed lemon juice. It allows you to make the ink invisible without using technically complex equipment and specific tools.
To carry out a simple experiment, you need to prepare the following materials:
- 1/2 part lemon;
- white sheet of paper;
- cotton swab;
- water;
- capacity;
- lamp;
- tablespoon.
Step by step instructions for making simple sympathetic ink using citrus juice:
- Squeeze the juice from half of the lemon pulp into a container. Add a few drops of plain water to the citrus liquid.
- Using a spoon, stir the 2 liquids.
- Dip a cotton swab into the solution and write the text on a white sheet of paper.
- Wait until the juice dries completely so that it becomes completely invisible.
- To reveal a hidden message, heat a sheet of paper by holding it very close to a switched-on lamp.
Freshly squeezed lemon juice is considered an organic substance that can oxidize and acquire a brownish color when heated. In order for the symbols with letters to completely disappear from the surface when applying the prepared solution to a sheet of paper, the citrus liquid must be diluted with water. Until the paper is heated, the message will be invisible.
A similar principle of action is characterized by wine with vinegar, onion juice, milk, honey and orange liquid. If you are interested in how to create sympathetic ink yourself at home using other methods, you need to try to conduct various chemical experiments, look at concentrated liquid solutions under ultraviolet radiation.
From milk
You can make invisible ink at home using a food product – milk.
To carry out the procedure, you must adhere to the following step-by-step stages:
- Pour a small amount of milk into a glass, dipping a brush into the container.
- Apply the text to a sheet of paper and wait until it dries completely.
- It is not recommended to dry paper in direct sunlight.
To reveal the hidden message, the text needs to be warmed up well. For this, you can use a candle, a warm iron or a lamp.
From citric acid
Invisible ink can be made at home using citric acid. The product is considered a simple and accessible raw material for conducting an experiment with a child.
To prepare sympathetic ink, you need to prepare the following materials:
- white sheet of paper;
- water;
- deep bowl;
- brush;
- citric acid of liquid consistency.
Detailed instructions for making invisible ink:
- Pour liquid citric acid into a deep container and add a small amount of water. The acid does not need to be diluted with liquid, but the ink will initially be slightly visible on the surface of the sheet.
- Mix the prepared mixture thoroughly.
- Wet the brush in the solution and apply the text onto a sheet of paper.
- Wait until the solution is completely dry.
- To read the hidden text, warm up the sheet using an oven, candle, iron or table lamp.
Citric acid, like citrus juice, can oxidize under the influence of elevated temperatures, acquiring a brown tint. The most accessible options for making invisible ink were presented above. Such experiments at home help to activate the child's cognitive activity, awakening his interest in chemistry. At the same time, this is considered a good method to attract peers and make spy games exciting.
Video about making invisible ink
How to make invisible ink: