Copper is a low-activity metal that is often used for decorative purposes. The article discusses the main methods of changing the color of copper at home and in the laboratory.
OXIDIZING copper and brass
Copper is often used as a decorative element on buildings, including furniture, jewelry, and art objects. The metal surface enters into a chemical reaction when it comes into contact with oxygen, however, it takes several decades to complete it.
The fruit of the interaction of copper and air is patina - the same material, only with a greenish tint. Less common is a black or brown patina. Practice has shown that the color of the patina can be corrected by processing it special means or methods.
Under the influence of high temperature, chemical reactions occur in the yolk with the release of sulfur. The interaction of our metal with sulfur gives it a dark brown color. In order for the chemical reaction to proceed correctly, the actions must be performed exactly according to the instructions: first, eggs are boiled, then a copper product is added. The number of eggs depends on the size of the copper item. They are boiled for exactly 10 minutes, after which they are removed and cooled.
Chilled chicken testicles are cleaned and finely kneaded by any means at hand. Next, you need a small container with a lid and a wide bottom. Place the copper piece and crushed testicles in a container. Make sure that both ingredients do not touch, otherwise colored spots will appear on the metal product and blackening will end in failure.
The combined ingredients are closed in a container for 20-30 minutes. It is worth noting that the result of the experiment depends on the duration of their stay together - the longer both ingredients stay in a confined space, the darker the metal you get.
Advantages of the method: to darken the metal requires few resources: a couple chicken eggs, an old iron container and gas stove... Disadvantages of the method: short-term and unstable effect. The results achieved may be lost over time or when exposed to reaction with a more aggressive chemical.
This darkening method is considered one of the best for darkening copper. Sulfide is a very active substance that must be used carefully at home. His hit in Airways may cause unpleasant symptoms nausea, dizziness, etc.
The metal must be prepared - wash it in warm water and soap. Otherwise, dust residues and greasy spots will interfere with the normal passage of the chemical reaction.
Further, a reagent is prepared - sulfide. It is sold in three flavors: liquid, gel, and solid. The shelf life of the reagent varies depending on its state of aggregation. For example, liquid sulfide is stored for no more than 2 weeks, while solid sulfide is stored for several decades. Please check the date of manufacture before purchasing.
To carry out the reaction, you will need an empty container where solid sulfide is diluted or where liquid is poured. Dilute the reagent with water only (it can be cold or hot, there is not much difference). Be careful not to let its vapors enter the respiratory tract.
The entire procedure is best done outdoors or in a well-ventilated area. With regard to hand protection, it is best to wear protective gloves made of rubber or latex on your hands to prevent contact of the corrosive substance on the skin. For additional protection wear regular glasses over your eyes.
If for any reason sulphide gets on the skin, then the affected area must be rinsed abundantly with running water. The same is done if it gets in your eyes. If the reagent penetrates inside, it is necessary to provoke vomiting and immediately consult a doctor.
Depending on the type of substance, it must be prepared in different ways:
A cold or slightly warm solution is needed to darken the copper. Before throwing the metal into the solution, you need to prepare a solution of water with soda in a ratio of 1:16. Soda neutralizes the action of an aggressive substance and will instantly stop its action.
The copper salt changes color.
Put a copper piece or product in a container and watch the reaction carefully. Remove the product only with metal tongs. Once the blackening reaches the desired consistency, remove it from the sulfide solution and place it in baking soda to stop the reaction.
If blackening is too slow, then the container can be slightly warmed up, this will speed it up. For even more acceleration, you can add 5 milliliters of ammonia. It is worth noting that the presence of ammonia gives copper a reddish tint rather than black.
If the copper is too dark, it can be lightened with a regular detergent powder. Apply a little powder to a hard surface of a washcloth and scrub well. Then the product is washed in warm water.
This method produces green or Brown color copper. To prepare the mixture, you will need: ammonia solution, baking soda, water and empty container. Before proceeding with the color change, the part must be prepared - washed in warm water and wiped dry.
When working with ammonia, it is necessary to observe safety measures: carry out experiments only in a well-ventilated area, wear gloves on your hands and protect your eyes from harmful vapors and splashes.
To obtain green copper, blackening must be carried out with: an empty container where 0.5 l is poured. vinegar, 125 ml of iodized salt and 375 ml of ammonia (pure). The required ingredients can be purchased at the store and pharmacy. The amount of salt added affects color saturation. Dip the copper into the prepared mixture for a few seconds and watch the reaction carefully. As soon as you are satisfied with blackening, remove the item and rinse with water.
Copper can also be made brown. For these purposes, you will need baking soda, water, and a bottle. Soda must be added to the bottle until it stops dissolving. Put metal object into a container and fill it with the prepared mixture. It is highly discouraged to use sprayers and other methods of applying soda solution to copper. This will give the copper object an uneven coloration.
The damp object is wrapped in a plastic bag and left that way for 1-8 hours, depending on the contrast you want the color to be.
Thus, you can change the color of copper at home. For this you will need metal container with a lid, water, copper product, soda, vinegar and ammonia. Most of the ingredients listed are sold at the grocery store and pharmacy. When conducting experiments, do not forget about safety - use goggles and rubber gloves.
Copper is a low activity metal and for this reason is often used for decorative purposes. Copper is used to make jewelry, home furnishings, art, furniture and much more. The surface of the metal is oxidized by oxygen, but due to its low activity, this may take tens of years. The consequence of this reaction is patina - a surface film that most often has a greenish tint. Patina prevents the metal from damage, so it is important to know how to blacken the copper at home.
Copper before and after blackening
There are two types of reactions that lead to the formation of films on the copper surface:
If you dip a copper product in a solution intended to form a patina on its surface, it will immediately transform and, being sparkling new, will look like an old one. There are two main types of methods that achieve this effect, some are based on improvised means, while others require chemical solutions. They can be dangerous, so you need to work in accordance with all safety rules. The room must have a fume hood.
Before you start blackening, you need to prepare the metal: clean, degrease, rinse and dry. For drying, do not use the towel wiping method. This can lead to the fact that there will be remnants of fabric on the products, water in the recesses of the relief, damage to the decorative part. Sawdust can be used for this purpose.
One of the most common methods is using sulfuric liver. It can be purchased at the store or prepared at home. To do this, mix powdered sulfur with potassium chloride in a 1: 2 ratio and put on fire in a tin can. After a few minutes, the powder will melt and, after 15 minutes, baked, its color will become dark brown. This process can be accompanied by a flame, which does not need to be brought down.
The first method, in which sulfuric liver is used for blackening copper, is as follows: 10–20 grams of powder is dissolved in one liter of water, or two to three grams, if it is necessary to obtain a not intense color. The copper product is dipped into the solution until the color changes, then taken out, washed and dried. The color turns out to be brown-gray and its shades.
Almost black color of the product is obtained by heating, after processing in a solution of sulfuric liver with water and the addition of ammonia. Alcohol must be added to the saturated solution until it turns clear blue. A coin or copper jewelry is dipped into the solution, and then heats up until it turns black.
Another method of obtaining black-brown color is as follows. Platinum chloride is applied to the product, for example, moistened with a brush. If the solution does not have an acidic reaction, hydrochloric acid is added to it.
A reddish-brown patina can be obtained with a one-to-one mixture of copper sulfate and zinc chloride. The mixture of powders will need to be mixed in the same amount of water and the copper product should be lowered there for a few minutes.
Patination of copper with ammonium sulphide gives a black color. The substance (20 g) is diluted in a liter of water. You can either dip the product into the solution or apply it with a brush. A reaction occurs on the surface resulting in the formation of copper sulfide. If you heat the plate before patinating, then depending on the temperature, you can adjust the shade of the resulting color.
Blackened Copperwork
Another way to obtain a black color is to heat a coin or jewelry at a high temperature in a solution of ammonium persulfate (9.25 g / l) and caustic soda (50 g / l). The temperature should be 90–95 degrees, the warm-up time should be 5–25 minutes. Repeat two to three times until the desired effect is achieved.
A light brown patina can be obtained by coating the product with the following solution:
Apply the freshly prepared solution with a brush, hold for four to five hours, rinse and dry. The procedure must be repeated three times.
The green patina is obtained by two main methods:
To obtain a coating with high wear resistance, which protects the metal from corrosion, per liter of water take in grams: 50–70 Berthollet's salt, 40–50 copper nitrate, 80–100 ammonium chloride. The product is placed in a bath with a heated solution for 10-15 minutes. The color ranges from brown to olive.
You can get amazingly beautiful golden patina. For this, 0.6 grams of copper sulfide, 180 g of milk sugar and the same amount of caustic soda are taken per liter of water. Aqueous solutions of the last two components are prepared separately and only then mixed. Copper sulfide is added only after the mixture is boiled. The product is placed in a solution heated to 90 degrees for a quarter of an hour.
A black-brown patina can be obtained with a boiled egg. The effect lies in the interaction of the metal surface with sulfur, which is released in the yolk when high temperatures... To do this, you must first boil the eggs, and only then add a copper product to the water. Depending on the size of the product, you will need a different number of eggs.
Another option. After the eggs are hard-boiled (10 minutes), they must be removed from the water and cooled. Peeled eggs are crushed and placed in a container with a wide bottom, and copper is also placed there. The container closes for 20-30 minutes or more, depending on what color you want to achieve: over a longer time, the product will darken. The main advantages of this method are simplicity and availability. The main disadvantage is that the effect is unlikely to be long-term and the coating will wear off.
Patina has excellent properties. For example, in numismatics, the cost of a product depends on how uniform it is. Artificial turf will not replace natural.
If the patina has a uniform structure and evenly covers the surface, then it is better to preserve it on the product. This is especially true for antiques and coins. To prevent damage to the top layer, it is necessary to take care of the product and handle it with special care. Do not clean with abrasive products or tools. And it is better not to touch the product with your hands.
But if it has chips, spots, looks ugly or heterogeneous, then such methods will do quite well. If you want the patina to lie flat, then the old layer must be cleaned to a metallic sheen.
This compound can be used for cold blackening of copper and copper alloy parts.
The coating has good corrosion resistance and can be used as a final finish. If the part is additionally oiled, the corrosion resistance can be increased and a deeper, more saturated black color can be obtained.
This coating is not suitable as an undercoat for painting.
Despite the fact that this coating is matte, it is recommended to polish the surface of the part. If the surface contains oxides, grease stains, deep traces of corrosion, etc., it is necessary to carry out mechanical processing (grinding or sandblasting).
Before applying the coating, the surface must be cleaned of grease, residues of polishing pastes, greases and oxides.
For this, the part after mechanical preparation must be processed in stages with intermediate rinsing in solutions. "UNIVERSAL CLEANER" and "ACTIVATOR".(See "Instructions for Surface Preparation"). During the surface preparation processes, it is necessary to carry out high-quality washing of parts. In case of poor-quality washing, the part after preparation may become covered with an oxide film, on which the coating is deposited extremely poorly.
Blackening copper
After surface preparation, you can proceed directly to the blackening of copper. This process is chemical and does not require the use of a power source and anodes. To carry out the process, the part is simply dipped into the blackening solution and held there. certain time... In order to avoid uncovered areas on the part (due to the formation of bubbles), it is necessary to periodically swing the suspension with the part fixed to it.
After rinsing, the parts are immersed in the fixing solution and kept there for the required time. During this process, it is also recommended to periodically wiggle the suspension with the part. Before carrying out the curing process, using a hydrometer, measure the density of the solution. If necessary, adding a fixing reagent to it, bring its density to a value of at least 1.1 g / ml.
The parts do not need to be rinsed after the fixing solution.
After the fixing solution, the part is dried. After drying, the surface of the part is oiled (by dipping or wiping) in industrial oil with a low viscosity, heated to a temperature of 35-40 ° C. Higher corrosion resistance of the oxide film can be obtained by oiling the part in hot linseed oil.
The easiest way to blacken copper is with ammonia vapor (ammonia). A denser color is obtained if the product (the wire is pre-soaked in a solution of sodium chloride for several hours).
An internet survey showed. that this is not the only method. Most of the information I found on the forum with ship modelers: http://shipmodeling.ru/
Bringing the scale of copper products closer to ship modelers and striving for a good and lasting effect. I chose those recipes that forum participants give as proven in practice and for which, in principle, you can find materials:
1. Buy special compositions for blackening (bluing) metal in a store for jewelers or in a store for hunters. (Not cheap!)
2. Prepare black mordant for copper: Dissolve copper sulfate in warm water. The solution needs to be saturated, i.e. add vitriol until it dissolves. Add ammonia until the mixture turns a bright transparent blue color. The workpiece to be processed must be immersed in the solution for several minutes, removed and heated until the part turns black.
3. Spread with sulfuric ointment and put in a warm place (on the battery) for several hours. True, they say that the coating is not very durable.
4. Prepare a simplified version of the sulfuric liver solution, in which potash is replaced by soda ash. Here is more detailed description process: " A ceramic bowl with a handle, like a pot. In 150 ml of distilled water, I dissolved two tablespoons of soda ash (bought in a household chemicals store in a package similar to washing powder), brought it to a boil and began to pour in colloidal sulfur (bought at a flower fertilizer store), also two or three tablespoons. The yellowish solution began to darken and after 7-8 minutes it acquired a brown color. Either I did not calculate with grams in a spoon, or the water boiled away, but in my opinion the required liquid was not enough and I added more water to the eye and boiled it more. The final liquid turned out to be a slightly yellowish-greenish tint. At the bottom there is a thick layer of yellowish sediment. Gently poured the resulting liquid.
My cannons are made of copper-plated lead. Commercial products did not give a stable coating, and this cloudy liquid gave my copper products a radical black color within 1 minute. The staining is stable, unlike my store-bought ready-made reagents, and even. It lends itself to polishing with a brush, but becomes a dark dark gray and begins to shine. "
5. And, finally, one more recipe (though there is only a link on the forum, no one has used it): Dissolve 4 g of caustic soda (caustic soda) and 4 g of milk sugar in 100 g of water, boil for 15 minutes, then, with constant stirring, add in small doses 4 g of a saturated solution of copper sulfate. Well-cleaned copper products are immersed in the hot mixture. Depending on the duration of the action, they will acquire different colors - from gold, green to complete blackness.
Milk sugar is a product baby food... Here is a link to the manufacturer (among the distributors there are store addresses in Russia).
I'll make a reservation right away that I am not a chemist, and all knowledge is only those that have remained from school. Therefore, the recipe was not fully followed and some deviations were allowed.
Processing lasts 25-30 minutes. at a temperature of 15-30 ° C.
In this case, when the recipes mention copper carbonate, in fact, they are usually talking about basic copper carbonate. To obtain it, you can use copper sulfate, acetate or nitrate. TO aqueous solution one of these salts is poured into a solution of potassium or sodium carbonate (potash, soda). The precipitated green-blue precipitate consists of basic copper carbonate of variable composition, nCuCO 3 x mCu (OH) 2, where n and m can vary in some aisles, which is not very important for us, in this case. The precipitate is filtered off, washed with water and can be used.
To blacken brass using this method, you will need:
The vitriol was bought at the nearest hardware store in the department that sells all kinds of pesticides to combat garden pests.
Soda - in the nearest grocery store, where there is simply plenty of it.
Ammonia - at the nearest pharmacy. But only 10%. As they explained to me, 25% is not for sale because of its danger.
First, prepare the copper carbonate. For this we need copper sulfate and regular soda. |
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 | Dissolve vitriol in warm water. The solution needs to be saturated, i.e. add vitriol until it dissolves. The solution must be made so that it takes up only half of the container. |
 | Then slowly, little by little, add the soda to the saturated vitriol. Precisely because the solution begins to boil like soda, I recommend making vitriol in just half the container. |
 | We stir. The seething dies down over time. I poured the baking soda until the bubbling stopped. After a while, you will see that a finely dispersed suspension of a pleasant turquoise color has turned out. On the surface, you can see that there is still a fry seething. |
 | Now the resulting suspension must be filtered. There was nothing worthwhile at hand, except for napkins. The recipe says dry. But I didn’t do it. |
 | Now we need a 25% ammonia solution. As I already wrote, only 10% is available in the pharmacy. So we will use it. |
 | Little by little we add turquoise porridge to ammonia. The solution turns blue. |
 | We also need a saturated solution. Therefore, we add, without sparing, copper carbonate. You will end up with a bluish black liquid. Here she is what we need. |
The solution is ready, it remains to lower the necessary parts there. Blackening time, according to the recipe, 25-30 minutes.
If the part is overexposed in solution, copper carbonate will settle on it in the form of turquoise crystals, which, in principle, then it will not be difficult to scrape off with a fingernail without damaging the blackening;
If there are difficulties in removing blue sediment from a part, I recommend simply heating it in a candle or lighter flame. The sediment will immediately fall off by itself.
