Types of sympathetic ink. Start in science

The use of sympathetic (invisible) ink implies a writing that is indistinguishable under normal circumstances, but appears after chemical or physical development. This is a variant of steganography.

The process of using good sympathetic ink (not to mention making it...) includes the following nuances:

– the recording is made on a sheet of high-quality paper with a thin and long wooden tip soaked in the necessary ink (for example, a toothpick or a match wrapped in cotton wool), a thin felt-tip pen, or a thin brush; the main thing is that this “pen” does not scratch the paper;

– both before and after writing, the sheet is carefully smoothed on both sides in different directions with soft matter, hiding the secret writing in the surface layer of the paper;

– the sheet with the secret writing is steamed, and then clamped between the pages of a large book and dried well. If traces of “chemistry” appear on it or they are visible under ultraviolet rays, the recording is rejected;

- if everything is in order, then on the sheet with hidden information they write an open letter or some other harmless invoice (say, a poem...).

To protect yourself from amateur attempts to reveal secret writing at random, you can use various tricks, including, say, nitration of paper (it will flare up when overheated...) or recording with a "light pen" (LED...) on paper that is very sensitive to light (what is written disappears on background from flare when illuminated by daylight...).

To manifest secret writing, you must use the appropriate reagent and appropriate technique. The developer itself is applied here by touch - rubbing with a sponge (cotton swab), through spraying from a spray bottle, or in another accessible and optimal way. Temperature variations involve ironing or heating near a light bulb.

As acceptable ink for secret writing, you can use many of the substances that come to hand: medicines, household chemicals, certain products, and even human secretions. A short list of sympathetic inks of this kind with a mention of their developer is presented below. The dry substances here are dissolved in water or in alcohol, and the concentration of the composition is established experimentally.

1. Beer and white wine are the ashes of burnt paper (the text is slightly moistened by the breath...).

2. Sugar water and factory-made apple juice - paper ash (when the text is moistened).

3. Apple juice (when “dipped” into an apple) and milk (diluted)

– heating

4. Onion and rutabaga juice - heat.

5. Food grade citric acid – benzyl orange.

6. Pyramidon (in alcohol solution) – heating.

7. Astringents for disinfecting the mouth and throat - heating.

8. Aspirin – iron salts.

9. Phenolphthalein - any diluted alkali (say, slaked lime...).

10. Alum - heating.

11. Sulfuric (battery) acid (at 10‑15%) – heating.

12. Wax (at least somehow a pointed fragment of a candle...) - calcium carbonate, or tooth powder (sprinkle and shake off).

13. Washing powder - light from an ultraviolet lamp (say, from a currency sampler...).

14. Saliva is ink that is very diluted with water.

15. Urine – heating.

16. Blood - (with considerable dilution) - a weak (0.1%) solution of luminol (1 hour) with bicarbonate of soda (5 hours).

Sometimes the so-called “water pressure” method can be very convenient, following which you need to moisten a sheet of unlined paper with water and place it on some kind of glass substrate (say, on a mirror...). Another dry sheet of paper is placed on this sheet, and then the required text is written with a hard pencil or thick ballpoint pen. While the paper is wet, the text will be visible, but as soon as it dries, it will disappear. After the sheet becomes dry, some kind of camouflage message is written on it using water-insoluble ink. For the hidden message to appear, you just need to stick the leaf into any water and immediately pull it back out.

We have to admit that some types of ink have either long since disappeared from use, or are used only for such mysterious purposes as secret correspondence. There are many methods for this type of secret writing, and they all use secret or "sympathetic" ink - colorless or slightly colored liquids.

Secret (cute) ink
This ink has the property of producing invisible writing, which becomes noticeable only after special processing.

Blue ink
Inscriptions made with a solution of 1 g of crystalline cobalt nitrogen salt or cobalt chloride in 25 g of distilled water are completely invisible; When the paper is slightly heated, they acquire a bluish color, which disappears when cooled.

Cobalt oxides......................... 100 g
Nitric acid...................... 300
Dissolve and mix with the solution:
Sodium chloride......................... 100 g
Distilled water........... 100
What is written in ink is invisible. Develop by heating over a lamp.

Yellow blood salt......................... 10 g
Water................................... 100
Write with this solution.

To develop, wet the paper with the following solution:
Ferric chloride......................... 200 g
Water........................... 500 ml

Red ink
Write with a diluted solution of gold chloride and allow to dry. Written: disappears. After moistening the written areas with a solution of tin salt, inscriptions appear purple-red.

Disappearing Ink
Mix 50 g of iodine tincture with a teaspoon of dextrin and filter. Anything written in such ink disappears within a day.
Dextrin, white or yellow powder obtained by processing starch; solution in water is a sticky liquid. To obtain dextrin, starch is heated to 180-200° or heated to 50° with dilute acids. It is used as an adhesive instead of gum arabic, for finishing fabrics and
leather, in the manufacture of inks and paints, to impart hardness and shine to linen, etc.

Grandfather Lenin's recipe
In childhood, for one whimsical game involving guessing the secret plans of their older revolutionary brother, little Ulyanov was given the nickname “Wizard” by the children. He dipped a clean quill pen into milk and wrote with it on a piece of white paper. The milk was allowed to dry, after which not a trace remained of the letters. Then Ilyich heated the paper over the glass of the lamp, and what was written clearly appeared on it.

Twenty years later, in a St. Petersburg prison, the old man again recalled his childhood. He broke a loaf of black bread, fashioned inkwells from the crumb, collected a white liquid in them, salty to the taste, and wrote with it between the lines in books on how to combat thrush. When the warden called his superiors to look at the quirks of the German spy, Lenin put the inkwell in his mouth. He moved his lower jaw with relish, never ceasing to praise the tsarist regime. Books were regularly handed over to the public. The workers whiled away the evenings free from meetings by reading them syllable by syllable at the firebox of the blast furnace. In the hidden text, the words of propaganda leaflets and the theses of the draft party program were vaguely discernible.

Secret Organizations' Recipe
Members of the secret organization “Black Redistribution” also used invisible ink in their correspondence. But due to the betrayal of one of the Black Peredelites, who knew the secret of deciphering the letters, almost everyone was arrested... The secret letters were written with a diluted aqueous solution of copper sulfate. Text written in such ink appeared if the paper was held over a bottle of ammonia. The letters turn bright blue due to the formation of an ammonia complex of copper.

Chinese recipe
But the Chinese emperor Qing Shi Huangdi (249-206 BC), during whose reign the Great Wall of China appeared, used thick rice water for his secret letters, which, after the written hieroglyphs dried, did not leave any visible traces. If such a letter is slightly 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 use of sympathetic (invisible) ink implies a writing that is indistinguishable under normal circumstances, but appears after chemical or physical development.

The process of using good sympathetic ink (not to mention making it) includes the following nuances:

The recording is made on a sheet of high-quality paper with a thin and long wooden tip soaked in the necessary ink (for example, a toothpick or a match wrapped in cotton wool), a thin felt-tip pen, or a thin brush. The main thing is that this “pen” does not scratch the paper.
both before and after writing, the sheet is carefully smoothed on both sides in different directions with soft matter, hiding the secret writing in the surface layer of the paper.
the sheet with the secret writing is steamed, and then clamped between the pages of a voluminous book and dried well. If traces of “chemistry” appear on it or they are visible under ultraviolet rays, the recording is rejected.
if everything is in order, then on a sheet with secret information they write an open letter or other safe text, a drawing with a pencil or pen.

To protect yourself from amateur attempts to reveal secret writing at random, you can use various tricks, including, say, nitration of paper (it will flare up when overheated) or recording with a “light pen” (LED) on paper that is very sensitive to light (the writing will disappear against the background from illumination during daylight illumination).

To carry out secret writing, you must use the appropriate reagent and appropriate methodology. The developer itself is applied by touch - by wiping with a sponge (cotton swab), by spraying from a spray bottle or in another accessible - optimal way. Temperature variations involve ironing or heating.

Reagent recipes

The dry substances here are dissolved in water or in alcohol; the concentration of the composition is established in practice.

Beer and wine. Developer –
Sugar water and factory-made apple juice. Developer – ashes of burnt paper (the text is slightly moistened by breath).
Apple juice (dipped into an apple) and milk (diluted). Developer – heating.
Onion and rutabaga juice. Developer – heating.
Food grade citric acid. Developer – benzyl orange
Pyramidon (in alcohol solution). Developer – heating.
Astringents for disinfecting the mouth and throat. Developer – heating.
Aspirin. Developer – iron salts
Phenolphthalein. Developer – diluted alkali (for example, slaked lime).
Alum. Developer – heating.
Sulfuric (battery) acid (at 10 – 15%). Developer – heating.
Wax (sharpened fragment of a candle). Developer – calcium carbonate, tooth powder. Sprinkle and shake.
Washing powder. Developer – ultraviolet lamp light.

The “water pressure” method can be very convenient, following which you need to moisten a sheet of unlined paper with water and place it on some kind of glass substrate (say, on a mirror). Place another dry paper sheet on this sheet and write the required text with a hard pencil or an empty ballpoint pen. While the paper is wet, the text will be visible, but when it dries, the text will disappear. After the sheet becomes dry, some kind of camouflage message or inscription is written on it with water-insoluble ink. For the hidden message to appear, you just need to wet the sheet a little.

Steganography

This art is based on an attempt to hide the very existence of a secret message, and therefore its techniques deserve the widest use. Indicative examples of these techniques (leaving aside the possibilities created by electronics) can be:

writing by pricking letters in a specific place in a certain book or newspaper (the ends of words are marked by pricking between the letters);
communication of some data (set of goods, wholesale prices) in a certain order;
writing using knots;
recording on the side surface of a deck of cards selected in a certain order (the deck is then shuffled);
notes on the reverse side of the labels of bottles, cans, bottles;
text under the affixed postage stamp;
writing on the inside surface of a matchbox;
writing inside a boiled egg (they take a mixture of alum, ink and vinegar, write with it what is needed on the shell of an ordinary egg, which is then kept in strong brine or vinegar to erase traces from its surface; then the egg is boiled hard, and the entire the text appears on top of the squirrel under the shell);
using a “damaged” typewriter, in which some letters are placed above or below the line (the order and number of these letters, as well as the intervals of their appearance, are taken into account here; Morse code is possible in the code);
broadcasting certain compositions on the air of the desired radio station, in a certain order or at a certain time;
handwritten notes in a music book (notes have meaning in Morse code or another code);
records in the form of a cardiogram or a graph of some technological process (here, when using Morse code, higher peaks indicate dashes, and what is lower - dots, dashes between teeth - a section between letters, line breaks - the end of a word);
entries only in the vertical columns of a completely filled crossword (horizontal lines are filled in arbitrarily, but the message itself can be either direct or coded);
stencil entries, in which a stencil with windows cut out in it is placed on a sheet of notepaper, following which the true message is written; the rest of the space is carefully filled with empty content, so that the words of genuine information are clearly included in the text of a clear camouflage message.

List of used literature

INK: SYMPATHIC INK

To the article INK

Sympathetic ink, also called invisible or secret ink, remains invisible to the naked eye until it is processed to reveal it. The definition of “sympathetic” was first used for such ink by the French chemist N. Lemery in his Cours de Chymie (1675).

Historical reference. Philo of Alexandria (1st century AD) was the first to indicate the composition for such ink; he described a method of writing using an extract from ink nuts and treating a document with a solution of iron-copper salt, which gave the written text a dark blue color. Ovid (43 BC - 18 AD) recommended to lovers the method of secret writing with milk, revealed by sprinkling soot on the paper. After the soot is blown off, tiny particles remain on the paper, stuck to the places where the letters written with milk were. Pliny the Elder (c. 23-79) in his Natural History mentions the juices of plants, the inscriptions of which were revealed in the same way. There is information that in the 9th century. Arab priests wrote the name of the Prophet Muhammad on stones with sympathetic ink, and these inscriptions became visible from the heat of the hand that touched them. In medieval Europe, secret ink was often used by scammers to demonstrate similar “miracles.” During the period from the 14th to the 17th centuries. The papal court, Italian city-states and other countries used secret writing to transmit secret diplomatic correspondence. During the North American Revolutionary War, invisible ink was used by both American colonists and the British.

The simple sympathetic ink used before World War I was fairly easy to detect. During both world wars, the use of such inks became widespread, and the composition of the inks became more complex, making them difficult to identify. Modern methods of studying documents have reached such a level that there is now hardly any secret ink that could not be discovered.

Types of ink. Sympathetic ink is classified in various ways. E. Mitchell and T. Hepworth distinguish them by color during development, and F. Marzival - by detection methods. Another method of classification is determined by the nature of the ink, which can be based on: 1) blood and body secretions (sweat, saliva, urine); 2) food solutions and juices of fruits, vegetables and plants; 3) chemicals (acids, bases and salts); 4) various substances, including soap solutions and the sticky substance of plants. Quite common substances available in liquid or solution are also used: acetic acid (colorless vinegar), cherry and citrus juices, soda ash and baking soda, rice, salt, sugar, water, alum, aspirin, gum arabic, boric acid, borax, starch, ammonia, magnesium sulfate (Epsom salts), copper sulfate, silver nitrate (or argyrol) and iodine.

The materials on which you can write with sympathetic ink are varied. Paper is most widely used, fabrics are used less often, while glass, wood, metals and plastics are rarely used. Some types of sympathetic ink require specially prepared surfaces to write on.

Detection methods. When studying documents, optical, mechanical, thermal and chemical methods are used to detect secret writing. Optical methods include viewing in visible light, penetrating light, ultraviolet light from a quartz lamp and infrared rays, as well as the use of photography. Visible light is directed directly or obliquely at the document, and the document itself is placed on frosted lighting glass, and the illumination is created by an incandescent lamp with a frosted bulb located underneath. With this transmission, the inscription containing silver nitrate darkens and becomes visible. Penetrating radiation can be directed directly, obliquely, or almost parallel to the surface onto the document. Many types of ink fluoresce in ultraviolet rays.

Mechanical methods include: 1) sprinkling paper with a fine powder of graphite, ocher, antimony or iron oxide; 2) exposure to iodine vapor; 3) moistening with water, iodine solutions (sometimes with the addition of potassium iodide), ultramarine or other dyes.

Thermal research is usually carried out by exposing the writing to a moderately heated body, such as an iron; In this case, care must be taken not to damage the document. Lettering containing potassium nitrate is detected by touching it with an open flame, causing the compound to decompose. Caution should be exercised as some acids will degrade both the lettering and the paper.

Chemical methods include: 1) exposure to ammonia, hydrogen peroxide or hydrogen sulfide vapors; 2) moisturizing with special solutions; 3) immersion in a chemical bath; 4) taking contact photographs with or without the use of special chemicals. Modern methods of detecting secret writing leave criminals little chance of successfully using sympathetic ink.

Collier. Collier's Dictionary. 2012

Types of sympathetic ink. Start in science

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