Cryptography is good and interesting, but maybe it’s worth moving away from cryptography and turning to steganography, that is, hiding the very fact of a message by writing it with invisible ink?
It’s already here, but let’s put together a longer list...
The disadvantage of invisible ink is that it was mentioned by Ovid and Philo of Alexandria. That is, it is enough to check the correspondence once to detect the message. The same case described here with Lenin and milk was known to the tsarist secret police and Lenin’s correspondence was successfully read by the enemy.
However, invisible ink have been and are being used for many centuries, they were popular not only in the Middle Ages, but also in the First World War and even, sometimes, in the Second, despite the spread of radio. Actually, they are still used, but in other areas - for example, marking banknotes to identify the bribe taker.
So, let's look at invisible ink based on development methods:
Developing ink with heat
This is the most ancient method and the most primitive. Only the lazy spy from pre-Christian times did not know about it.
However, there is a twist to it - if the enemy has read the letter, then it will definitely not reach you, and what does reach it is unread. I think Lenin used precisely this property when sending a letter with milk.
Here you can use:
1.
Honey or sugar (it darkens at caramelized temperatures).
2.
Lemon, apple, onion (organic acids react with paper when heated).
3.
Milk (lactose dehydration).
4.
Blood serum.
5.
Soap (carboxylates are oxidized).
6.
Vinegar.
Here you can separately add a point 7
, cobalt chloride.
The fact is that in the first six paragraphs the inscription appears irreversibly and it is impossible to deliver the letter to the addressee in this form - it is clear that it has been read. Cobalt chloride turns blue when heated, and when it cools, the color disappears. Undoubtedly, it is a good idea to add it to paint enamel teapot to see if it has cooled down, but for secret writing...
Developing ink with chemicals
Here we will try not to mention ink that reacts to heat.
1.
Phenolphthalein, the most famous acid-base indicator. Accordingly, you need to develop letters with substances to which he reacts. The easiest way is to take soda or potash with an alkaline reaction.
It’s quite a hit-or-miss option, because phenolphthalein is obtained from phenol, which the hit-and-miss will still have to extract in order to obtain it for carbolic acid.
The disadvantage is that both acids and alkalis are too simple substances that the enemy will have available.
2.
Ammonia, that is, ammonia. It is manifested by a pH indicator made from red cabbage (the technology is primitive, google “red cabbage water”).
The method...let's just say it's bad.
Ammonia was expensive in ancient times, and the presence of secret writing is easily determined by smell, which is not a big deal at all.
3.
Copper sulfate. Occurs in nature in the form of the mineral chalconite. Manifested by sodium iodide, sodium carbonate, ammonia hydrate or red blood salt.
Quite a viable option. The main thing is the secrecy of obtaining chemicals for manifestation.
4. Lead nitrate. The connection has been used since the 16th century. Manifested by sodium iodide. For ancient times, the level of secrecy is very high.
5. Iron sulfate. Manifested by sodium carbonate or red blood salt. An ancient method.
6. Starch. Manifests itself in iodine compounds. Very interesting method, probably the most interesting. Starch is available, in fact, at all times. But it is still very desirable for the victim to receive it, for and not only.
7. Salt. It manifests itself as silver nitrate (“hell stone”, “lapis”). Something tells me that in the Middle Ages this method was very well known.
8. Cerium salt of oxalic acid. It is manifested by manganese sulfate or hydrogen peroxide. For the outsider, it is of purely academic interest.
Developing ink with ultraviolet light
The issue here is not the substances used to write, the issue is the ultraviolet. Nowadays there is a detector at any checkout in a supermarket, but it’s more difficult to build such a thing for a stranger.
But let's take a look at the substances:
1. Fluids from the human body - saliva, blood plasma. Well, for aesthetes - sperm (I just have a hard time imagining how to write with it, even with a pen). Nevertheless, the substances are extremely accessible, there seems to be no need to even continue.
2. Soap, lemon juice. But this is hardly suitable, because it is determined by heating. In this case, blocking the ultraviolet detector is stupid.
3. Sunscreen
4. Washing powder that contains bleach.
Several methods used in the First World War stand out separately.
1. Take raw egg, messages are written on its shell with vinegar. If an egg is boiled and peeled, the letters can be seen on the surface of the boiled egg. The method is very niche - it works over short distances and is hardly suitable for the Middle Ages. Well, maybe so - to convey news from a besieged castle (although this may turn out to be a lot).
2. There are a bunch of different methods with photographic paper, which simply require a developer in dark room, and the letter comes in black opaque paper. There are so many variations of this method that they need to be described separately. But does the hit-and-miss need it?
During the First and Second World Wars in the USA and Britain, all suspicious letters were scanned with ultraviolet and infrared rays, and treated with iodine vapor and ammonia vapor. This is how the Americans caught a German saboteur in 1918.
Therefore, here is a snack for you - the requirements for ideal invisible ink, formulated by British intelligence in the First World War:
1. Mix with water.
2. They do not have a pronounced odor.
3. Do not form crystals on paper, otherwise they can be seen in reflected light.
4. Invisible in ultraviolet light.
5. Does not decompose or discolor paper (like silver nitrate)
6. Does not react to iodine or any regular developer.
7. There should be as few potential ink developers as possible.
8. The ink should not react to heat.
9. Must be easily accessible and have at least one plausible innocent use in everyday life.
10. Not be a combination of several substances.
It is easy to see that points 7 and 10, as well as points 6 and 9, are incompatible with each other.
Nevertheless - last time The use of invisible ink was noted in 2008, when a notebook was discovered containing al-Qaeda phone numbers written in invisible ink.
Probably not in the kitchen anymore, but on paper. Let's do it DIY invisible ink.
It's great to use developing liquids for secret drawings, treasure maps, secret letters.
The first method is perhaps the most famous.
Invisible ink made from milk
Vlad was unable to write a letter with a brush; for now he can only manage it with a pen or pencil. I received this message one morning 
Therefore, they painted a landscape with milk, dipping a brush into it. After drying, we ironed it and the writing became visible.
This happened because the protein contained in milk burns at a much lower temperature than paper. Therefore, when heated, the paper remains white, but the milk already darkens.
Invisible ink made from lemon juice
Another way of chemically classifying messages iswrite with lemon juice.After drying, wipe with cotton wool and iodine. In place of the letters there will be bright spots. This is what they recommend in the book, but in practice it was hard to see. The result is a drawing - Africans in night Africa)))
This is a dad with his son and a truck on a string. We were not at all upset when we saw this result. Our grandmother had a lot of fun with her creation. And then Vladik and his grandmother drew a joint masterpiece.
Grandpa turned out to be very similar! By the way, I read that felt-tip pens are also indicators and react differently to acids and alkalis. But during our experiment, the stains from the felt-tip pens blurred equally, whether from a solution of soda or from vinegar.
But the Chinese emperor Qing Shi Huangdi (249-206 BC), during whose reign the Great Chinese Wall, used thick rice water for his secret letters, which, after drying the written hieroglyphs, does not leave any visible traces. If such a letter is slightly moistened with a weak alcohol solution iodine, then blue letters appear. And the emperor used a brown decoction of seaweed, apparently containing iodine, to develop writing.
And what creative continuation of the experiments would you offer your child? Share your ideas in the comments and send photos of experiences and experiments from your home laboratory. Thank you for reading our notes and sharing them on in social networks. We're committed to making science fun for you.
Happy experimenting! Science is fun!
The text of the work is posted without images and formulas.
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Introduction.
On New Year I was given a “Large Chemical Laboratory” kit, it came with instructions, it describes all the experiments that can be carried out. I was interested in one of the experiments on making invisible ink using the substance phenolphthalein and ammonia.
And I wondered, what other invisible ink exists, what are they made of, where did they come from, who invented them?
And of course, the greatest interest was raised by the question: can I, on my own, make such invisible ink at home?
Hypothesis: Let's assume that invisible ink exists and can be made at home.
Target: conduct experiments on making invisible ink.
Tasks:
Explore the history of invisible ink.
Find out what invisible ink is and how to make it.
Prepare necessary equipment, inventory, materials for making invisible ink.
Test your hypothesis about the opportunity self-made invisible ink at home.
Analyze results
Invisible ink is ink whose writing is initially invisible and becomes visible only under certain conditions (heating, lighting, chemical developer, ultraviolet or infrared rays, etc., etc.). They are also called sympathetic ink.
Since ancient times, invisible ink has been used to keep correspondence secret. The first invisible ink arose in ancient times.
The first recipe for invisible ink belongs to the Roman poet Ovid, he proposed using milk as invisible ink (appears after heating).
The Chinese emperor Qing Shi Huang, during whose reign the Great Wall of China appeared, used thick rice water for his secret letters, which, after drying, leaves no visible traces. But if the letter is moistened with a weak alcohol solution of iodine, then blue letters appear. And the emperor used a brown decoction of seaweed, apparently containing iodine, to develop writing.
The ancient Greek philosopher Philo of Alexandria described a recipe for sympathetic ink from the juice of ink nuts. In his case, the letters appeared after the writing was exposed to a solution of iron-copper salt.
In the Middle Ages, secret agents of Ivan the Terrible used onion juice to write their denunciations, and Vladimir Lenin also used lemon juice or milk for letters. To develop the ink, it was necessary to hold the letter over fire.
In later times, chemical inks became widespread. They were widely used by spies, intelligence agencies, and underground fighters.
Today, there is a special ink that only appears under ultraviolet light, which is used in the production of paper money.
Types of invisible ink.
Invisible ink appears when certain conditions and depending on the nature of the interaction of substances, all inks can be divided into the following types:
Chemical;
Photosensitive;
Luminescent;
Heat sensitive;
Moisture sensitive.
Chemical:
The composition of such ink includes substances that are colorless or weakly colored, which then, when interacting with other substances, acquire a bright color.
The chemical ink solution is applied to the paper and allowed to dry. The paper is then moistened with a developer substance and the “invisible” ink appears.
Photosensitive:
This ink appears or disappears when exposed to light. They can be divided into two groups.
The first group is ink that appears when illuminated. The second group is ink that disappears when illuminated and appears in the dark.
Photosensitive ink is applied to paper and air dried. The inscription is developed or removed by illuminating it with bright light.
Luminescent:
These inks contain colorless or slightly colored substances that can luminesce (glow) under the influence of ultraviolet radiation.
Luminescent ink is applied to paper. The paper is then illuminated with an ultraviolet lamp and the invisible ink begins to glow. After the ultraviolet radiation stops, the inscription disappears.
Heat sensitive:
These inks contain substances that exhibit color when exposed to heat.
The ink is applied to the paper and dried, at which point the inscriptions remain invisible. But as soon as the paper is heated with an iron, held over a fire or other heat source, the ink “appears.”
Such inks include lemon juice, onion juice, and milk. When heated, they most often turn brown.
The easiest way is to make and use heat-sensitive ink at home.
Moisture sensitive:
The writing produced by this ink becomes visible when exposed to water or steam.
Moisture-sensitive inks can be divided into two groups:
Translucent ink: after drying, the inscriptions are absolutely invisible on the paper, but if you hold the paper in water, the inscriptions become translucent. When they dry out, they disappear again.
Adhesive ink: inscriptions made with such ink appear when processed with steam and some colored powder. First, the paper with the inscription must be steamed, this will make the ink sticky. Then very fine colored powder is sprinkled onto the paper, and the remaining powder is shaken off. Particles of powder adhere to the adhesive ink and form an inscription.
Solutions of sucrose, glucose, and gelatin can be used as such ink.
Practical part.
From the Internet I learned that invisible ink was used in ancient times. People came up with and invented new ways to hide what was written.
Invisible ink alone requires chemicals, for others natural substances. And it turns out that there are several methods for preparing invisible ink that can be easily applied at home, using quite affordable materials.
Here are some recipes that every child can use to make disappearing ink:
Invisible ink from lemon - squeeze the juice of half a lemon and dilute it with the same amount of water, develop with heat;
Invisible ink from onions - prepare onion juice and use it as ink, develop with heat;
Invisible ink from milk - take milk and use it as ink, dry it, develop it over a candle or lamp;
Invisible ink from soda - prepare a concentrated solution of soda - 1 teaspoon per 10 ml. - 2 - 3 teaspoons of water, move everything, use as long-lasting ink, develop with heat.
I decided to use some available for homemade recipes and see if I can make such ink myself. I will also try one way to create invisible ink using chemical substances, using the chemist's kit I have.
Making invisible ink at home.
Experiment 1Making invisible ink from lemon juice.
For the experiment you need: lemon, glass, brush, White list paper, water, iron.
Squeeze the juice from the lemon into a glass and add the same amount of water. Dip the brush into the resulting solution and write or draw something on paper. After this, leave the paper with the inscription to dry.
After drying, take the paper and heat it with a hot iron.
Citric acid darkens when exposed to temperature, thus making the ink visible.
Lemon juice smells pleasant, is not noticeable when it dries, but it takes a long time to dry and appears as a faint yellow-brown tint to the letters.
Experiment 2Making invisible ink from milk.
For the experiment you need: milk, a candle, a glass, a brush, a white sheet of paper.
Pour milk into a glass. Dip the brush in milk and write something on a piece of white paper. Let the milk dry.
After drying, there will be no trace or smell left from the letters. Then we take the paper and hold it over the candle. Gradually the inscription begins to appear. The inscription appears brown; this milk changes color when heated.
But the color of the inscription turned out to be not uniform, and using a candle is not very convenient and safe because you are constantly afraid that the leaf may catch fire; it is much more convenient to use an iron. But the experiment made it possible to prove that the inscription appears under the influence of any heat.
Experiment 3Making invisible ink from lemon and iodine.
For the experiment you need: lemon, iodine, cotton pad, glass, brush, white sheet of paper, water.
Dip a brush into lemon juice diluted with water and write words on paper. After drying, the lemon leaves no visible marks on the paper. To read what is written, let's prepare a weak iodine solution by diluting the iodine with water. Soak a cotton pad in the iodine solution and rub it over the paper.
The paper is colored in Blue colour, and those places where the inscription was made remain white. This is explained by the fact that the paper contains starch, and it becomes visible when reacting with iodine, and the places written with lemon do not stain.
Experiment 4Preparation of invisible ink using phenolphthalein and ammonia.
For the experiment you need: phenolphthalein, ammonia, a brush, a white sheet of paper, latex gloves.
Before this experiment, be sure to put on rubber gloves on your hands, since you will be working with chemicals.
I found the substance phenolphthalein in my kit; it turned out to be a white, cloudy liquid. I dipped a brush into it and wrote an inscription on a piece of paper. Let it dry.
Then I took an ammonia solution from my kit. Poured ammonia into the container. Here you need to be very careful, you need to do this in a ventilated area, since ammonia has a very pungent odor.
I held my piece of paper with the inscription over the ammonia. After some time, my inscription turned pinkish. After the ammonia wore off, the inscription became invisible again.
Ammonia dissipates quickly, so my inscription was visible for only a short time.
Experiment 5Making invisible ink using a candle.
For the experiment you need: a candle, a brush, a white sheet of paper, paint.
I made an inscription on a white sheet of paper with a white candle. The leaf remained white. Then I took a brush, paints and painted the sheet with paint. The entire sheet was colored, except for those places where it was written with a candle. The text became easy to read against the background paint.
Conclusions.
1). You can make invisible ink at home from readily available household substances. I used milk, lemon, iodine, and a candle. Moreover, even a child can make them.
2). But not all types of invisible ink can be made at home. Some inks require chemicals that are not readily available at home. For some you need ultraviolet lamps, who are also not always at home.
3). In the course of my work, I became convinced that experiments are very exciting and interesting activity. But it is better to carry them out together with adults, since heating elements were used for the experiments, and in one experiment, chemicals.
4). When developing ink with heat, it is more convenient to use an iron than a candle, since holding the paper over a fire risks the paper catching fire.
5). When heated, the substances contained in lemon and milk are destroyed and become Brown color. And the starch contained in paper turns blue when in contact with iodine.
Conclusion.
In the course of my work, I studied the history of invisible ink and what types they come in. I learned many ways to make invisible ink and I made some of them myself at home.
Thus, I completely confirmed the hypothesis put forward at the beginning of my work: invisible ink exists and can be made at home.
The purpose of my work was to conduct experiments on the production of invisible ink, and I achieved my goal in the process of this work.
List of used literature and Internet sites.
https://ru.wikipedia.org
http://cryptohistory.ru/
http://www.krugosvet.ru/enc/nauka_i_tehnika/tehnologiya_i_promyshlennost/chernila.html?page=0.1
http://www.patlah.ru/etm/etm-13/dom%20tipografia/sekret%20cernil/sekret%20cernil.htm
Instructions for the set “Big Chemical Laboratory”
Invisible ink is a collective name for compounds that, once applied to paper, are invisible to the naked eye and appear after treatment with reagents or changes in temperature. Similar writing instruments were used in diplomatic correspondence and intelligence.
Below are simple recipes, available to all novice spies and conspirators. The necessary ingredients can be found in every kitchen, found in any chemical kit, or purchased at the nearest pharmacy.
Read also:
Invisible ink recipes
So, what can we do with our own hands at home? And a lot of things!
Cow material
Pour some milk into a glass. We write the secret message with a thin brush or a cotton swab; in extreme cases, a toothpick, a feather, or an ordinary sliver will do.
Having entrusted information to a piece of paper, it should dry thoroughly, preferably without resorting to direct sunlight: ultraviolet radiation is destructive to spy secrets. After making sure the milk is dry and invisible on paper sheet, you can send it to an accomplice.
You can make text visible by heating the paper. In our hasty times, this is usually done using an iron.
Sometimes a secret document is put in the oven, heated near a light bulb, and if the message is not so urgent, it can be placed on a warm radiator. True fans of spy traditions use a candle flame and nothing more.
"Juicy" ink
After cutting the lemon, squeeze the juice into a cup, add a few drops of water, and stir. We can use a fresh apple in a similar way: after grinding the fruit on a fine grater, we squeeze out the juice we need. If you don't have an apple, you can take an onion.
You will have to experiment a little with the ratio of juice and water: if the concentration of acid in the composition is too high, the fresh inscription will stand out against the background of the paper and will no longer be secret, otherwise the developed text will turn out unclear.
The time spent is repaid by the ease of use of the resulting solution: if you are too lazy to fiddle with brushes and sticks, you can pour it into a fountain pen. After writing, dry. Develop by heating the paper.
Rice to work!
The ancient Chinese once again confirmed their status as the wisest people on the planet by combining the exciting and therefore energy-consuming process of writing a secret message with cooking.
Thick rice porridge was cooked in such a way that some of the liquid remained on the surface without being absorbed into the rice. Dipping a brush into this liquid, they wrote a message. After completing the work, the narrow-eyed spy wiped the sweat from his forehead, left the paper to dry, and, raising his head, a short prayer Buddha, began to eat.
The “delicious” recipe for invisible ink did not remain a Chinese monopoly for long; it was soon borrowed by scouts from the islands lying in the east.
So the young spy, devouring another portion of porridge left after a secret writing session to the delight of his mother, can rightfully consider himself a successor to the ninja traditions.
In ancient times, the “rice” inscription was developed by heating the paper. But the white-faced devils came up with an innovation here too: they began to cover the leaf with iodine. The text now appears more clearly.
Time-honored invisible ink recipes are listed. Let's move on to more modern methods in the style of James Bond.
Other recipes
There are other options for making ink. We have a dime a dozen craftsmen!
From... soda
Mix water and soda in equal proportions. We apply the text to paper and dry it in the shade. It is curious that the usual heating for developing text will not help, you should resort to help grape juice. By applying the juice with a brush over the entire surface of the leaf, we can read the message.
Starch
Add one part water to two parts, stirring, heat the resulting mixture over low heat, let it cool. Apply the text with a toothpick, match, or any wooden stick.
For manifestation cover the paper with iodine. The leaf will take on a delicate purple hue. The inscription will be dark purple.
Vitriol
Add a couple of pinches of copper sulfate to a glass of water, stir thoroughly until the crystals are completely dissolved. Apply the inscription with a brush, cotton swab or solution filled fountain pen. Dry in the shade. For manifestation hold the leaf for some time over the container with ammonia , under the influence of the vapors of which the text will turn blue-green.
Instead of washing
We dilute regular bleaching washing powder with water, make an inscription, and dry it in the shade. The text can only be seen under the light of an ultraviolet flashlight.
We use aspirin
Dissolve in water a regular aspirin tablet, and invisible ink is ready. We apply the text and dry it. You can read the message after treating the paper with a solution of iron salts, which are found in powder form in almost every chemical kit.
Using invisible ink you can write any words and draw different drawings. But then they will disappear! Surprise your friends at a party or birthday, write a secret note to a friend or spend interesting experience with kids. There are many ways to make invisible ink.
Making invisible ink from lemon juice
Squeeze the juice from the cut lemon into a bowl. Add a little water and stir. Let's test our ink:
- take a sharp small stick or thin brush. It’s good if you have a pen with a feather;
- dip a stick in ink and write something on a white sheet of paper;
- let the inscription dry - the message will become invisible;
- Iron the invisible inscription on the sheet with an iron, the ink will begin to appear.
You can hold a sheet of paper over a lit candle at a distance of 10 cm - a similar result will come out. The inscription will be brown. The same dark inscription from invisible ink after heating will be obtained when using apple, onion and other juices with a high acid content.
Making invisible ink from milk
Pour a little milk into a cup. Dip the stick in milk and write something on paper. Let the milk dry well on the sheet. To read the inscription, heat the piece of paper on a light bulb, over a candle, or iron it with an iron.
Making invisible ink from starch
The ink preparation process is as follows:
- combine 2 parts starch with one part plain water;
- heat the resulting paste over low heat, stirring all the time;
- let the paste cool;
- Use a cotton swab or a sharp wooden stick to write words on paper with cooled ink.
To manifest words, lubricate the piece of paper with an aqueous solution of iodine. The paper will turn light purple. And the words that appear from the ink will turn dark purple.
Making invisible ink according to an ancient Chinese recipe
Ancient Chinese emperors used rice water to send secret messages. Cook thick rice porridge. Make sure that the rice does not absorb all the liquid. Use this water as invisible ink. Write a message on paper. To develop the inscription, lubricate the paper with an aqueous solution of iodine.
Making invisible ink from baking soda
Prepare:
- water;
- grape juice;
- baking soda.
Combine water and soda in a one to one ratio. Mix them well in a bowl and you have a soda-based ink. Put them on paper, but heating will not help to reveal the secret message. Use grape juice. Dip the brush into the juice and paint the paper until the inscription appears.
You can use an oven instead of an iron, candle or light bulb to heat the sheet. Place the secret message in a hot oven and wait a few minutes for the message to appear. Invisible writing appears on a sheet of paper when heated because the ink substance chars faster than the paper.
Remember to use safety precautions when displaying a message on open fire! Prepare a saucepan in advance cold water. In it you will extinguish the leaf if it accidentally catches fire.
Choose any ink recipe and surprise your friends or play spy. Even the secret agents of Ivan the Terrible wrote their messages to the Tsar with onion juice, and no outsider could read the message.