As soon as they do not call the patina in the world of numismatics - both the soul of an old coin, and the old rust that spoiled it appearance and "ate" the reliefs so dear to the collector's heart. What is the patina on coins, where does it come from, can it be removed and should it be done? Why does a noble patina appear on some coins, while others never have a noble rust? For those who are just learning the basics of numismatics, all this knowledge will be useful in order to correctly assess the coin in hand and its authenticity, and eliminate the temptation to do something that can turn a valuable rarity into a circle of worthless old metal.
What is patina?
The word "patina" has an Italian origin, in which it has a generalized meaning: the formation of a deposit, an oxide film on any surface of any material under the influence of factors environment... It can appear on anything, even on a stone. In fact, this is the same as rust, which is susceptible to iron, the only difference is in the chemical structure, which is due to chemical composition the object itself (in this case, metal). If rust appears on iron, patina forms on copper, silver and other non-ferrous metals.
Is patina on coins good or bad?
The question cannot be answered unequivocally. On the one hand, the presence of an oxide film confirms the authenticity of the coin, its age, and even gives a certain charm and translates into the category of antiques. On the other hand, it destroys its surface and spoils its appearance. As a result, the patina can both significantly raise the cost of an individual copy, and devalue it. Hence the conclusion: the patina is good only up to a certain limit, until the process of obvious destruction of the surface of the coin disc and the loss of the reliefs of its pattern began.
"Cabinet" patina
Even proper storage does not provide complete protection against oxidation of the metal surface. However, the difference in the end result can be palpable. If the coin is stored in a hermetically sealed capsule that restricts air access as much as possible and is made of a non-corrosive material, the oxide film will slowly and accurately lay down on its surface. This is exactly the patina that is called noble. In some cases, experts call it a cabinet.
The word "office" in this context does not mean a room, but special lockers from varnished wood with drawers lined with velvet - the so-called muntskabinets used by numismatists of past centuries. By and large, velvet and wood did not carry the functions of high-quality storage, but served more for the effective presentation of the collection. The plaque with such storage turned out to be beautiful, but rather thick. Hence, the term "cabinet wear" was subsequently formed, applied to specimens that were not in regular circulation, but were not kept in the best possible way.
This term applies to cases where the specimen has been in the ground for a long time, simply in the air, in a humid place or in another extremely aggressive environment. The resulting patina when stored this way is rough, thick and ugly. Moreover, it is no longer a thin film of plaque, but eats into the metal itself, becoming an inseparable part of the coin. If it is cleaned of patina, but it is not smooth and even, depressions will be visible in it and reliefs may become indistinguishable. In the most advanced cases, the metal crystallizes completely, i.e. virtually disappears and the coin disc is one continuous patina.
For patina, dirt is sometimes taken into the grooves of the relief. You can distinguish them by the coverage area. Real age plaque always touches part of the smooth field, and dirt accumulates in the folds of the pattern.
Patina types depending on the alloy
Different metals oxidize in different ways, which means that the type and color of the age plaque that has appeared is different. This is due not only to the parameters and shelf life, but also to the composition of the alloy, including all its impurities. For example, if there is even a tiny fraction of iron in the composition, the patina will have a characteristic reddish tint. It is the impurities that cause the appearance of an oxidizing film on coins made of precious metals.
Patina on silver coins usually due to the impurity of copper, and gold money discs would not have any traces of oxides without the presence of impurities, since gold of the highest standard is usually used for minting, and it is practically not subject to oxidation. However, on gold specimens, dots or minor streaks of a darker color (up to brown) can often be observed, which betrays the presence of copper.
The first sign of patina on silver coins is a slight yellow coating, then it turns crimson, turns blue-green and finally turns dark gray or almost black.
Patina on copper coins
Copper is the leader in oxide film formation. Copper oxide has a color close to black, sometimes it can be lighter brown. The well-known green color of aged copper is formed by its sulfides and sulfates. If loose beads appear on the surface with greenish tint, which means that we are dealing with copper chloride, which behaves the worst and in a short time destroys the metal, leaving deep traces after cleaning it ("bronze disease").
In addition, surges have to be dealt with if the coin is artificially aged. And, finally, there is one more type of patina on copper coins, which is called "malachite". It looks noble and beautiful, has an amazing blue-green color and represents the thinnest crystalline layer.
Modern metallic money
As for modern samples, which are based on stainless steel or a copper-nickel compound, their surface is oxidized slowly and weakly, the color of the plaque varies from gray to copper-golden. Aluminum discs lose their shine and acquire a nondescript grayish coating. Brass coins deteriorate very quickly, starting to darken or losing color and becoming almost white after a few months. Good storage can slow down this process in certain cases. If a brass alloy is exposed to chemicals, it takes on a red tint.
Another type of modern coins is steel with electroplated non-ferrous metals. The slightest damage to the coating, almost invisible to the eye, causes a violent oxidation process, as a result of which the entire applied film swells, and the metal under it rusts. It is highly doubtful that such coins will ever be able to acquire a noble appearance in old age.
Classification of the patina of old coins
The different type of oxide film depends not only on the composition of the alloy, but also on the conditions in which the old coin was located and some other subjective factors. In numismatics, there is the following classification.
It is an exquisitely noble plaque formed under conditions of careful maintenance. There is a characteristic transition from almost imperceptible changes to a darker color in the direction from the center to the edge of the coin. Sometimes the dark areas are not located along the outer circumference, but in separate places of the coin field. This aging is considered beautiful and adds value to the old coin.
In this case, the plaque is more heterogeneous in color, the transitions do not have precise localization, but are smooth and do not have sharp shade boundaries. The reason for this uneven aging is the inhomogeneity of the composition due to poor mixing of the alloy. This is not a disadvantage, but rather indicates the authenticity of the coin, minted in conditions far from ideal. About 200 years ago, technology did not yet allow obtaining a perfectly homogeneous metal.
Iridescent patina
This is the name of a homogeneous plaque that changes color depending on the angle of view.
Pantry patina
As the name implies, we are talking about the oxidation of the surface of coins that have been lying in a closed container in the ground for a long time, that is, they have not had direct contact with it. but external environment with such storage, it is still too aggressive for the high-quality preservation of the treasure. Outwardly, it is a thick brown layer that has eaten into the metal. After removing such a deposit, cavities remain on its surface. If the coins are made of silver, then they speak of "horny silver", which looks like bulges due to contact with soil chlorides.
Formed exclusively on copper samples that were stored in sand. Outwardly, it looks like an even beige-yellow bloom.
Artificial patina
The high value of old coins is often the reason for the artificial induction of age signs. This is not always done for the purpose of unjust enrichment. For example, artificial aging is used when creating official copies or after cleaning, the result of which is an unnatural color for the metal or an obscene shine for the age of the coin. In addition, patina is applied in order to visually hide some physical defects as a result of regular walking or improper storage. In any case, artificial "old age" with a certain skill is easy to distinguish from natural, no matter how beautiful the result looks. There are several ways to obtain it.
Tinting
On the scale of professionalism of aiming an artificial patina, this method is at the lowest level and is applicable only for mass production of cheap copies. The first obvious sign of a fake is gloss, which in a genuine case should not be, a thick layer of plaque and its sharp drop in places where the transition to the center should be very smooth. However, it is possible to deceive completely ignorant people with such fakes.
Burning
To give the coin disc the old look, it is heated over an open fire of any type - a gas burner, blowtorch, fire, etc. Another short-sighted technique, since the difference is too obvious.
Chemical methods
They can be different, but they boil down to imitation of conditions that provoke an accelerated aging process. The inventions of entertainers are innumerable, we will give just a few examples:
- A solution of copper sulfate and potassium permanganate based on distilled or simply boiled water, heated below the boiling point. The coin is lowered into it for a short time (a couple of minutes).
- Rubbing with sulfuric ointment, followed by rinsing in a solution of ordinary laundry soap.
- Immersion in any sulfuric solution or in sulfuric acid itself. Even ordinary match sulfur is used. The impact is very strong and fast. But the result is also easily recognizable.
"Folk art"
The same can be said about him as about chemical experiments, with the difference that natural aggressive media are used without the use of active substances. These are all kinds of combinations of temperature effects, humid air, water and even food (as an example, baking a coin in a potato). Sometimes it is possible to get good results, however, well distinguishable from the originals by specialists. But without the proper skill, most often the result is a hopelessly damaged coin.
How to determine if a patina is artificially induced:
- Too abrupt transitions from dark to light areas, excessive dark color in hard-to-reach places of the relief and along the edge of the circumference of the coin field.
- Shine. The true patina is always matte and has no sheen.
- The presence of shades unusual for metals. The most common example is the red tint of brass, unmistakably indicating the use of chemistry.
- Upon closer examination, it is possible to distinguish between cavities or scratches under an even film of plaque.
- The distribution of patina depends on the height of the relief, while in the natural case it does not.
An artificially aged coin does not add value, numismatists even claim that a true collector feels the “soul of a coin”, its noble gray hair. Such a statement is equally difficult to both prove and disprove, so we can only talk about physically obvious parameters. The only acceptable exception to artificial processes can be considered the method of accelerated oxidation in the natural environment, but this still takes many years.
Hello dear readers. In the next article we will tell you what coin patination is and how to do it. Cleaning and patinating coins are almost always related to each other. Often, after the cleaning process, we get an unnatural shine of the coin or an unpleasant shade of color. “Now take off half of the starting price,” the forum experts grumble as they examine your freshly cleaned copy. A coin patina tool or manual patina can be used to restore a coin to its usual appearance. Methods of patinating coins depend on the metal with which we have to work.
Patination theory
The word "patina" seems to us originally Russian, like "old" or "homeland", but it came to us from the Italian language. It appears thanks to chemical reaction transforming the surface of the coin. On silver or copper, the patina looks beautiful, while the patina on an aluminum coin is a cloudy film, which is why such specimens lose value. The mottled or partial patina also does not add to the charm of the coin. Therefore, the patina disfiguring the appearance of the coin is removed. It should be remembered that the patina is part of the coin... If the oxidation processes have affected the deep layers, then after cleaning, instead of a coin, we will get a thin plate with shapeless holes instead of a pattern. But even well-preserved coins can look unsightly after cleaning. This is especially true of copper coins, which acquire a reddish color. However, it is possible to return the coin to the look of undisturbed antiquity. For this, patina is used - the process of creating an artificial patina.
Availability of targeting patina
To an untrained collector, it seems that in order to create a patina, one must be almost a medieval alchemist or work in a large chemical laboratory. This is not true! Most types of patina are induced in simple ways using the available ingredients. Despite the fact that the patination of coins is the application of an additional layer that gives the surface of the specimen a beautiful color, the defects of the coin induced patina will not hide. Dark spots, potholes, nicks, smudges, etc. will remain in place, only change color. According to seasoned collectors, artificial patina will not add anything to the price of a coin. But the patina brought by experienced hands is no different from the natural one, and the coin takes on a very attractive look in the eyes. potential buyers... Patina induction processes for different metals have cardinal differences. Simply put, there is no universal method. Let's take a look at some.
Copper Coin Patination
There are a great many ways to put a patina on copper. The method using manganese and copper sulfate is very popular. If there is only a standard package (3 grams) of manganese, then take 10 grams of copper sulfate per half a liter of water. If manganese is taken in an amount of five grams, copper sulfate will need already 20 grams per liter. We heat the solution to 90 degrees. When the desired temperature is reached, place the coins in the solution. The temperature should be controlled by heating the solution and periodically turning the coins. The result: a wash-resistant, bright brown patina. Pay attention to the toxicity of vitriol and take the measures required when working with toxic substances.
Fixer (sodium hyposulfite) is used to put a patina on clean and fat-free coins. We soak the coins in the solution from 10 seconds to half a minute. The removed coins are wiped with a cloth. When the coin is dry, patina will give it a bronze color. The simplest way is to heat a coin in a burner flame. gas stove when the test specimen turns light brown. Copper plating is also an easy option, albeit less popular. Patinating coins with sulfuric ointment is also not a difficult method. Work must be carried out in water. Rubbed with ointment, the coin gets a patina of dark brown or grayish color. For clarification, after a forty-minute pause, the coin is first polished with a napkin, and then washed with a soapy brush. The experts do not recommend sulfuric ointment, but it is quite suitable for experimenting with simple methods.
Patination of silver coins
Silver is advised to patinate with ammonia (an ordinary bottle of ammonia). For half an hour, the coin is placed in the freezer. Fixing the experimental specimen with tweezers by the edge, hold it from a minute to three over the open vial. Once the coin has acquired the desired gray color. Then we rinse the coin in water and dry it. For those who don't want to mess with ammonia, a simple hard-boiled chicken egg will do. It is cut into pieces and covered with a glass jar along with a coin placed on the edge. Coin patination in this way is fast: the color change is visible by eye. However, if you are not satisfied with the color, it will not be easy to wash off the induced patina.
When everything happens by itself
If you put a patina on bronze coins , then you can use methods suitable for silver. But there is a way of naturally patinating bronze coins. For this, bronze coins must be exposed to sunlight at all times. The sun helps to obtain a beautiful and even patina on bronze in one and a half to two years. Of course, this method cannot be called an express method, but you don't have to wait half a century either. Coming back to copper, consider the tips for keeping peeled coins in a match jar. The results are ambiguous, but you can experiment on inexpensive copies. At home, they try wood patina. Certain types of wood produce tannins, which contribute to the production of "cabinet" patina.
What is patina?
Oxidation is called rust. Oxidation of other metals - patina. The first is being fought. The second is being chased.
They are chasing not to expel, but, on the contrary, to keep. Collectors, for example, say that “ patina on coins- this is the life experience of banknotes ”.
The plaque testifies to the antiquity of the exhibit, the careful attitude towards it by the previous owners.
However, in addition to the natural patina formed when the metal interacts with the atmosphere, the environment, there is also.
When purchasing other antiques, you should check the "authenticity" of the plaque.
Patina application
Patina application artificially done not only in order to deceive inexperienced treasure hunters and collectors.
The main purpose of the man-made film is decorative. People are happy to buy doorknobs, objects, vases and antique ones.
There is no need to look for true monuments of antiquity, to pay fabulous sums for them. You can simply buy an item with an unnatural patina.
It is created using various oxidizing agents. They are included in special mixtures.
Thus, the "AK" company produces a whole range of liquids and ointments for aging the creations of aircraft modeling circles and clubs.
Having bought a standard set of parts for an airplane model in a store, for example, you can make a unique copy from a designer.
The above company offers compositions that form a patina on,, gray metals.
By the way, the so-called - also "the creation of patina hands." It comes in a variety of colors.
Patina on metal
On some metals there is a film, on others it is red, on the third. The tone of the plaque also depends on the conditions in which the item was stored and used.
On the city streets, the patina is greenish. But, there are metallic ones, with a touch of other paints.
These are already artificially obtained copies. How you can put on the same metal in different "clothes", we will tell you with an example.
Black metal appears after lowering it into the liver. It is a mixture of caustic and.
For obtaining artificial patina its thick mass is diluted in water. The solution is heated to 70 degrees Celsius.
Sometimes, the product is not completely dipped in the composition. This is done if you only need to blacken individual sites or a decor item.
Oddly enough, but there is also an old one with an unnatural touch. The art of recreating the patina was possessed in the ancient.
Pliny the Elder testified to this. The writer, who arrived in Egypt from Rome, recorded: - “They do not mint here, but paint.
Dust and sulfur are mixed with it. with additives are remelted in a tightly closed vessel from ".
They learned to paint in greenish-gray only in the 20th century. Then they mixed iodide, water and.
Metal was dropped into the solution and it was covered with a noble film. It represents nothing more than iodide.
Under the influence of light, the plaque is partially destroyed. From under the green "haze" the clean base is visible in places.
You will not see the golden and brown patina. Either this is not possible, or the necessary reagent has not yet been invented.
Only copper, bronze can be coated with a brownish bloom. A dark shade of "wenga" gives a solution of the same sulfuric liver.
Paints are achieved using copper sulfate. The reaction requires a mixture of a substance with water and potassium permanganate.
The metal is kept in the mixture for 4.5 minutes. The experiment will fail if the surface is not pretreated. It should be fat-free, dry.
Man-made patina is effective, but does not always protect the item. There is no metal base at the interface between the film and the metal base.
This is a layer that prevents further corrosion. It is he who slows down the process of destruction of antiques.
For example, it takes about a hundred thousand years for a coin to turn into sand. Without cuprite, the metal would turn to dust much faster.
The features of the middle layer between the products and the film covering them were discovered in the USSR.
In the union state, the repatination method was widely used. They removed the historical plaque and replaced it with an artificial one.
The latter was more aesthetic. But, after processing, some values began to deteriorate quickly.
Scientists grabbed their heads, and they figured out the causes of the disaster. While studying the composition of natural patina, physicists and chemists discovered cuprite and its properties that save metal.
From a chemist's point of view, plaque on copper or silver coins is surface oxidation. Like rust on iron. But it is precisely the patina that gives the antique coin a special charm, which is the evidence of its authenticity and makes the coin unique. The patina is the result of the aging of the coin, but aging in good conditions... The beautiful patina indicates that the coin was stored carefully and correctly. Sophisticated numismatists believe that the patina is the life experience of the coin, its soul.
Western dealers have noticed that the veneer of the ages is appreciated by experienced collectors, while novice numismatists prefer shiny coins.
“Some collectors are afraid of patina coins. But such fears are unreasonable. Antique coins, especially silver ones, take on different shades over time. This is one of the most beautiful features of old coins that distinguishes them from modern coins, and I hope that collectors who have not yet appreciated the value of the patina coins will learn this. "
That is, whether the patina will add value to the coin is a matter of personal preference. The evaluation criterion is subjective - oxidation looks beautiful or ugly on this particular coin. Not all patina is considered attractive. If the patina, for example, lays down uneven spots or stripes, then the coin is considered to be damaged by the external environment.
Natural patina is formed over time under the action of chemical substances, which are present in small quantities in the atmosphere. For example, compounds containing sulfur. Some collectors claim that silver coins do not oxidize at all. This is not entirely true. It's just that if the coin is stored in a stable environment, for example, in a sealed case, then the metal will "absorb" all sulfur compounds available in this environment, and this will stop the patina formation.
Types of patina
Different metals are patinated in different ways. It is believed that the patina on silver coins is generally more attractive. Small amounts of hydrogen sulfide in the air lead to the formation of silver sulfide on the surface of the coin. Coin albums, leather wallets, or canvas bags can release hydrogen sulfide. The color of the patina on a silver coin can vary from iridescent shades of yellow, crimson, turquoise to black. Ancient silver coins from excavations are usually black due to exposure to sulfur-containing amino acids, which are formed as a result of decomposition of organic matter.
Although most often the patina on silver is the result of reaction with sulfur, silver also reacts with other substances from the environment. For example, with chlorides contained in the soil, which manifests itself in unattractive gray and black spots. They protrude slightly above the surface of the coin. The so-called "horny silver" is formed.
Sometimes a silver coin owes its patina to the metal in its alloy, such as copper. Coin containing copper may turn green. Copper and its alloys - bronze and brass - are more susceptible to chemical reactions.
Brown or black patina on copper caused by copper oxide and sulfide, green and blue - by various copper salts: chloride, acetate, carbonate. "Bronze disease", which manifests itself as powdery green or green-blue spots, consists of copper chloride and hydrochloric acid and can completely destroy the surface of the coin. "Disease" is contagious, and coins affected by it should be kept separate from all others.
Antique bronze coins can have a beautiful “earthy” or “sandy” patina. This sandy-beige coating appears due to microscopic grains of silicic acid salt, which are found in sand or sandy soil.
Gold, the least reactive metal, retains its original appearance. But gold coins made with copper or silver may have a deep orange patina. Some gold coins develop light brown or dark orange dots or streaks called copper spots. They can be caused by poorly mixed copper.
Nickel usually covered with a slight, light, smoky gray patina. Sometimes it has a pale blue or slightly golden hue. Nickel coins can become stained due to PVC compounds (polyvinyl chloride, polyvinyl chloride) when stored in vinyl holders. The iridescent patina on the nickel is most likely artificial.
Patina color depends on the thickness and antiquity of the oxidized film. The early patina on silver has a yellow color, later turning into lilac-red and only later - into greenish-blue and black. Coins different types patinated in different ways, depending on how they were made. For example, the nature of the patina is influenced by the concentration of acid with which the coins were processed at the mint. And also a combination of a variety of factors: whether the coins were touched with greasy fingers, what material were they stored in the case, at what humidity, etc.
Many unsightly patinated silver coins have suffered from the treatment with thiourea to remove plaque. Coins washed in it may look attractive, but overexposed ones lose their luster and look lifeless. If after processing the coin is not properly rinsed, then over time it will become stained and corroded.
"Cabinet patina"... "Cabinets" in tsarist Russia were called special lockers for storing and presenting coins. They were made of fine wood and finished with velvet. "Cabinet" was supposed to match the collection and its owner, as it testified to its high status and good taste. The patina was formed under the influence of the vapors of wood and varnishes, which covered the cabinets-cabinets. Abroad, the term "cabinet patina" is rarely used.
There are many types of patina: wild patina, "bullet" (color changes from the periphery of the coin to its center), rainbow patina (with many colors), iridescent (sparkling, colors vary depending on the viewing angle). Such coins are priced more expensive by some grading companies, which encourages craftsmen to artificially impose a patina, deceiving collectors.
The masters of giving "killed" coins a decent look, as well as creating a patina are artificially called "coin doctors".
The fake patina is also unpleasant because traces of a more serious "treatment" of the coin - scratches from improper cleaning, contact damage and even sealed holes and cracks - can be hidden under it.
Methods for creating artificial patina
An artificial patina is considered if there is an attempt to create it in a short time. There are many ways to patination: baking a coin in the oven (sometimes inside a potato), roasting blowtorch, aging in a sealed container with crushed match heads, soaking in a thin layer of acids, bleaches and sulfur-containing chemicals. There are other technologies that require more time to implement: keeping the coin under the sun on a windowsill or oak boards (analogous to the “cabinet patina”), wrapping it in carbon paper, or simply sealing it in a regular envelope with the addition of sulfur.
On copper coins, the patina is obtained by soaking copper sulfate and potassium permanganate in a solution heated to 80 degrees. Often a small amount of sulfuric ointment is rubbed into a coin under running water, after which the remnants of the ointment are washed off with a solution of dishwashing detergent.
Grading companies expose many fake patina coins every year.
Most characteristic signs artificial patina:
* rounded patina spots due to uneven staining of the dye used;
* colors flow into each other in the wrong sequence. On coins with a natural patina, the sequence is as follows: first yellow, then red-purple, then green-blue;
* unnatural colors on silver coins - khaki, pumpkin orange and pale blue;
* patina is localized on the surface of the coin, has no depth and is not immersed in metal;
* patina rests over scratches or other marks;
* patina has bright, "felt-tip" colors;
* patina has a yellow-brown, smoky color.
Artificial patina is often considered a significant flaw in the coin. And natural, depending on the personal preferences of collectors and dealers, can be regarded as an advantage.
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Preserving coins is no different from preserving any items made of copper and its alloys. Although such finds are referred to as "massive archaeological material", but this does not give a reason to treat them at random.
What is hidden under the word "conservation"? Conservation measures ensure the preservation of the material existence of the monument and prevent further loss of the original. Conservation is aimed only at preserving pure substance, while not paying attention to aesthetic enhancements. Many believe that coin preservation is all about coating. Far from it. Conservation includes various conservation work carried out directly at the facility. For example - cleaning and fixing the original surface, as well as preventive conservation measures. For example, optimization of climatic conditions, correct packaging, presentation and storage.
Before talking about conservation measures, I would like to remind once again about such a concept as an original surface. There is no such term in numismatics and general practice, but there is a concept - patina. Unfortunately, this is too much general definition oxide film, which often does not give any idea about the state of the coin, and hence the choice correct methods conservation. Although it is customary to divide the patina into "noble" and "not noble", but often this very statement leads to the fact that the preserved original surface and its details are removed, guided by outdated aesthetic concepts.
What is the original surface? The original metal surface of the coin is replaced by metal salts during the corrosion process. Due to the fact that this transformation is very slow, such a layer reproduces the nuances of the original surface. But, unfortunately, corrosion products and soil particles often cover the relief details and distort the shape. The original surface is not only the carrier of the relief, but also gives us a good guide when cleaning the coin. This is a kind of border, beyond which we cannot step (except in rare cases). Everything that is above the original surface can be called dirt, everything below is the original.
The picture shows a section of a coin taken with an electron microscope. The boundary between the original surface and deposits (dirt) on the surface is well traced. There is a layer of corrosion products under the original surface.
It often takes a long time for a coin to land on the restorer's table. During this period, poorly preserved coins can suffer significant irreversible damage. Several factors are primarily at play here, one of which is the mishandling of an unstable patina.
In general terms on this topic, we can say the following:
1. After removing the coin from the soil - do not rub or try to clean the find in order to see it better. The find should be handled with extreme caution.
2. Try to immediately determine the state of the patina and if damage is found (porous structure, cracks and chips, bumps and growths, missing surface fragments, etc.) in a dense layer of patina, be sure to wrap the object in a damp cloth moistened with distilled water (or just a damp ground) and place in a tightly closed box. In this way, we prevent the patina from drying out. In addition, the risk of physical damage to the patina caused by vibration and shock is minimized.
3. Try to reduce the time between retrieval of the find and the start of desalination (flushing) to a minimum. For a long time, the find should not be in a damp cloth, otherwise there is a risk of subsequent corrosion. This is especially true for items that have active foci of bronze disease.
4. Perform preliminary clearing (flushing from the ground) only if the patina is stable.
5. For all finds with a damaged patina (it does not matter if it peels off or not), the process of washing the salts is required. But it must be taken into account that prolonged rinsing has a negative effect on the state of the patina. Important: to determine the optimal flushing time. Usually, for finds with a thin layer of patina, this period does not exceed two days. If the patina allows it, it is recommended to remove loose dirt with a soft brush and distilled water. If there is a likelihood of flaking patina, then there can be no question of any preliminary trimming.
I would like to focus on rinsing with distilled water. The purpose of washing is not to soften oxides and soil residues, but to remove soluble salts in the patina capillary system. Any plastic box with a tight-fitting lid will do for this. The cover not only prevents water evaporation, but also prevents gases and salts from entering the air. The container must be completely filled with water, otherwise there is a risk of the ingress of harmful substances from the air gap. The coins should be as close to the surface of the water as possible. You can use a plastic strainer to do this. In the course of desalting, it is necessary to turn the coins at least once, so the process of the release of salts from the underside of the coin is much faster. This should be done not with your hands, but with tweezers. You cannot climb into the water with your fingers.
:!: Important: the destructive power of distilled water should not be underestimated. Distilled water is the best solvent for salts, including those that make up the patina. Excessive exposure of coins to distilled water can lead to irreversible damage. :!:
Exactly how many coins should be in the wash can only be determined empirically, by measuring the concentration of salts with a solimeter or by determining their quantity and quality in other ways. As a rule, the layer of dirt, including oxides, on the surface of the coin does not exceed a few millimeters. In this regard, the process of salt release is relatively fast and takes from 24 hours to several days.
To improve the result, after the rinsing period has expired, it is necessary to take out a coin with tweezers and wrap it in a wet napkin moistened with distilled water (clean, without added perfume or oils). Press the soaked cellulose slightly with a brush to the coin, so that it is in full contact with the surface. You can use and toilet paper but not bleached with chlorine. Then place the cellulose-wrapped coins on the wire rack in a dry place. It is imperative to wait until the surface of the compress is completely dry and only then carefully remove it. When dry, the salts migrate from the capillary system into the compressed material.
Salt washing is obligatory for all coins, except for those with a dense, undamaged patina.
Finds with a noble patina can be simply rinsed with distilled water.
Determining the safety of coins
Ideally, the metal surface of the coin, or the entire coin, is converted to mineral during the corrosion process without changing the shape of the object. There is only the substitution of one material for another. Thus, the surface of a copper coin is replaced by a new surface, for example, a malachite surface. The formation of such a patina can be called pseudomorphosis. The emergence of a noble patina is directly dependent on the environment.
Depending on the mineral formed, the color of the coin's surface can vary greatly.
Here are some examples of this patina:
Patina, which has an even, monochromatic color, is the most preferred by collectors. But, not all coins have such an original surface. In many cases, the process of converting a metal to a specific mineral does not occur evenly. As a result, the coin takes on a non-uniform hue. At first glance, such a patina does not look very aesthetically pleasing, but it is she who is the source of information, namely the carrier of the relief.
Contamination and loss
If we talk about the state of the coin, then there are two main sub-points. Namely, pollution hiding relief (original surface) and loss. As already mentioned, everything that is on top of the original surface can be attributed to pollution. But not infrequently, the pollution itself is a source of information. So, for example, in the corrosion products deposited on the surface, you can find the remains of organic materials, be it old vegetation or the remains of a wallet. In addition, pollution can tell us about the conditions in which the coin was in the ground, how polluted the atmosphere was at one time or another, what fertilizers were used in this area, or where this coin was generally found, and also give answers to many others. questions.
Speaking about contamination, two types should be noted here: layers formed in the process of corrosion and soil layers. Typically, both types of contamination are present at the same time.
Here are some examples:
In some cases, contamination covers the entire surface of the coin with a thick crust, making it completely impossible to determine the denomination, to read the inscriptions or the date. But still, under the layers of corrosion products and soil layers, there is always an original surface bearing numerous relief details.
The photographs below clearly show that the original surface can be found under the layer of dirt. The only question is how to properly clean such a surface and reveal all the preserved details, but we will return to this later.
Destruction and loss
The loss of the original surface can be attributed to irreversible damage that is practically impossible to restore. In this case, there is a loss of part or all of the relief of the coin. The destruction of the patina can occur as a result of mechanical damage, chemical action, as a result of changes in external conditions, changes in temperature, humidity (when the processes of recrystallization of copper salts in the corrosive layer can begin) or the washing out of unformed layers with water. This also includes damage caused by improper handling of an unstable patina.
Several examples of coins, the relief of which has been almost completely lost
Ten pfennigs 1912. The original surface is fragmentary. Under the layer of dark patina there is a bright red loose layer of cuprite. The thickness of this layer is relatively high.
General view of the coin.
The reverse side of the coin. Loss.
