Bronze painting: the choice of paint and the technology of its application. Features of decorative painting of metal surfaces Metal painting under bronze and brass

Usually, both pure black and gray coloration is obtained by the formation of copper oxide or copper sulfide on the surface of the thing. But both of these colorings can also be achieved by deposition of sulfur compounds of other metals - lead, bismuth, mercury, etc. on the surface of the thing. Will the coloring be completely black or light black, i.e. gray, depends both on the composition that causes the color, and on the time of action of the latter.

Parts must be prepared, the surface must be perfectly clean, free of dirt and grease.

Chemical blackening

Hold the part for five minutes in a solution in which 0.9 g of sodium hydroxide and 0.3 g of ammonium persulfate (NH 4) 2 SO 8 per 100 ml of water (it is used in photography). Solution temperature 90-100 o C.

The formation of black oxide of copper on the surface of things.

For the formation of black oxide of copper on the surface of things, the heated thing is immersed for several seconds in a solution of copper in excess of nitric acid and then held over a charcoal fire until its surface begins to turn black. To obtain a uniform and sufficiently dense black color, the operation is repeated several times, otherwise the color will not be completely black, but grayish. At the end of the staining, the thing is wiped with a cloth soaked in oil. Optical instruments are usually blackened in this way.

Blackening of brass and bronze.

For brass and bronze, the following solution can also be used: 2 parts of arsenic (not arsenic!) acid, 4 parts of hydrochloric acid, 1 part of sulfuric acid and 80 parts of water. Arsenic acid can be replaced with antimony oil (antimony trichloride). The thing is immersed in a solution heated to 50 ° C, and during the immersion, it is touched with a zinc stick.

Painted in metallic grey.

Very good staining gives a solution of the double salt of sodium sulphate and lead: dissolve 45 g of lead sugar (lead acetic acid) in 3/4 liter of water, and 150 g of sodium sulphate (hyposulfite) in 1/2 liter of water. Mix both solutions and heat to 85-93°C. The surface of a thing immersed in a solution is very quickly covered with a layer of lead sulfide. The color of this layer changes as it thickens and in the end becomes very beautiful - metallic gray.

Black staining with bismuth sulfide.

In a similar way, black staining with bismuth sulfide is obtained. To do this, the thing, painted, as explained above, with a brown bismuth nitrate solution, must be immersed while still hot in a strong solution of sulfuric liver (Hepar sulfuris) - the brown color quickly turns into black.

Without paint, many metal surfaces can be painted if they are coated (chemically or electrochemically) with a thin layer of colored oxides or salts firmly adhered to the surface. The last condition is not so easy to fulfill. For example, iron in humid air quickly (and without our help) becomes covered with a reddish-brown coating of oxidation products, simply put, with rust, but this method of painting is no good, because the rust barely sticks and gets dirty when touched.

Here we will give several recipes for coloring non-ferrous metals. Only some of them are suitable for a home experiment, the rest require chemicals that you can’t buy either in a pharmacy or in a photo store. However, we hope you have already signed up for a chemistry circle.

Copper and brass tarnish rather quickly in air. But they will retain their shine if they are chemically dyed. The preparation of the parts will take some time, because the surface must be completely clean, without traces of dirt and grease. Carefully wipe the polished part with a cloth soaked in gasoline, and then with wet chalk or tooth powder. After washing the part in running water, hang it on a harsh thread or fishing line and do not touch it with your hands anymore so as not to leave grease stains (even if the skin looks completely dry, there is still at least a little grease on it). Dip the part in a dilute solution of nitric acid (no more than 5-10 ml per 100 ml of water) and rinse again, preferably with hot water. Preparation completed.

What happens next depends on what color you decide to paint the copper. If it’s black, then hold the part for five minutes in a solution in which 0.9 g of sodium hydroxide and 0.3 g of ammonium persulfate (NH 4) 2 SO 4 per 100 ml of water (it is used in photography). The temperature of the solution is 90-100°C.

In a solution of potassium chloride, nickel sulfate NiSO 4 and copper sulfate CuSO 4 (4.5, 2 and 10.5 g per 100 ml of water, respectively), at the same temperature, copper and brass will acquire a pleasant chocolate hue. Brass will become azure after a short exposure to a mixture consisting of 3 g of lead acetate (lead lotion can be used), 6 g of sodium thiosulfate (hyposulfite), 5 g of acetic acid and 100 ml of water. The temperature of such a solution is about 80°C.

Copper can also be green. To do this, it must be lowered into such a solution: for 100 ml of water - 20 g of copper nitrate Сu (NO 3) 2, 30 g of ammonia and 40 g of ammonium chloride (ammonia) and sodium acetate; a solution of the latter substance is easy to obtain from soda and vinegar. Please handle copper nitrate with care, avoiding contact with the face and especially the mouth.

With the exception of the blackening experience, we do not state reaction times anywhere. Choose it yourself by experience, bearing in mind that the longer the processing time, the more intense the color.

The next metal that lends itself to chemical coloring is zinc. It is used infrequently, but everyone is familiar with galvanized objects - buckets, basins, troughs. The object of the experiment can be any old, unusable galvanized object. Wash its surface with a solution of soda or wipe it with a cloth soaked in gasoline, wash with hot water and soap and rinse several times. On a galvanized surface, we will apply mixtures of substances that will react with zinc; giving colored compounds. Here are the color recipes.

Black: 2 parts copper nitrate, 3 parts copper oxide, 8 parts hydrochloric acid and 64 parts water; after the appearance of color, rinse the surface with water and dry.

Green: 10 parts of copper sulfate and tartaric acid, 12 parts of water and 24 parts of sodium hydroxide solution in water (1:15); as soon as the color appears, immediately rinse the surface with water, otherwise there will be a brown tint.

Blue: for 100 ml of water - 6 g of any nickel salt and the same amount of ammonium chloride,

Golden: mix a solution of 1 part tartaric acid, 2 parts soda and 1 part water with pure clay; rub the surface with the mixture, and when it dries, rinse with water.

Brown-bronze: a mixture of 1 part verdigris and 5 parts acetic acid; rub the surface with the mixture, rinse with water and dry.

Copper: since zinc is more active than copper, it means that it is enough to moisten it with a solution of copper salt, for example, copper sulfate.

By the way, with such paints you can draw a picture on a zinc surface.

Let's move on from zinc to aluminum. It is somewhat more difficult to color it: there are more operations, and you cannot do without electric current. Aluminum oxide and salts are nondescript, so a different coloring method is needed. He is known for: anodizing. Its essence is that a current is passed through an aluminum part immersed in an electrolyte; in this case, an oxide film with a thickness of less than 0.1 mm is formed on the surface. Since the aluminum parts in the electroplating bath serve as the anode, the process is called anodizing. The oxide film is permeated with microscopic branched pores, in which dyes are well retained. It is possible to paint the anodized surface with organic dyes, including natural ones, but it is better with inorganic substances. Usually, the part is treated alternately in two dye solutions, and brightly colored reaction products remain in the pores.

Polish the aluminum part, degrease it with gasoline or acetone, rinse it in hot water and hang it on a wire. Dip the part for two to three minutes in a 5% sodium hydroxide solution, rinse again and immerse in a weak solution of nitric acid (20-30 ml of acid per 100 ml of water). Of course, it is no longer possible to touch the part, and if it is inconvenient to work with the suspension, help yourself with tweezers.

Rinse the parts again in hot and cold water and hang on a wire in a glass. You can put a stick or pencil on the edges of the glass and wrap the wire around it once or twice, picking up such a height that the part is a few centimeters above the bottom. Connect the workpiece to the positive pole of the current source. Cathodes - steel plates - hang in the same way. Batteries can serve as a current source, but they will “sit down” very quickly; a battery or transformer with a rectifier is preferable.

Pour a solution of sulfuric acid into the glass with the part (20 ml of acid per 100 ml of water; be careful!). Include a key or switch and a rheostat in the circuit to regulate the current. To measure it, you need a milliammeter, but a tester that many radio amateurs have is also suitable. Close the circuit and set the current at the rate of 20-25 mA per 1 cm 2 of the surface. The part will immediately be covered with gas bubbles - this is oxygen released, which oxidizes aluminum. At room temperature, the process takes about an hour.

Rinse the anodized part in running water and start painting. Immerse the part alternately in two coloring solutions, holding in each for 5-10 minutes and rinsing each time in running water. Rinse and dry the painted parts again.

Here are the compositions of coloring solutions and their possible concentration (in grams per 100 ml of water):

blue or blue color - potassium ferrocyanide (1-5) and iron (III) chloride (1-10);
brown - potassium ferrocyanide (1-5) and copper sulfate (1-10);
black-cobalt acetate (5-10) and potassium permanganate (1.5-2.5);
yellow-potassium bichromate (5-10) and lead acetate (10-20);
golden yellow - sodium hyposulfite (1-5) and potassium permanganate (1-5);
white-lead acetate (1-5) and sodium sulfate (1-5);
orange-potassium dichromate (0.5-1) and silver nitrate (5-10).

O. Olgin. "Experiments without explosions"
M., "Chemistry", 1986

Metal is widely present in our premises, and is used where its unique physical qualities compared to other materials are needed. However, often the metal also decorates the living area with its presence. And in order to make its visual characteristics even more interesting, the metal surface can be given one or another color or texture. By itself, metal painting is most often done for protective purposes, but the technique of decorative painting has a lot of differences.

Various metal objects, lamp covers, heating radiators, sinks and similar elements are most often subject to painting with decorative properties. At the same time, work can be carried out both for objects used indoors and for external metal elements.

Tips for those who are going to paint a metal surface at sub-zero temperatures

Although this advice may apply more to ordinary painting than decorative, situations are different. For example, you need to immediately paint a part that has just been brought from the cold. So here are some tips:

The best way to paint in the cold is to use alkyd enamels with a jelly-like consistency that have high adhesion (the ability to penetrate the surface structure);
Painting a surface cooled to temperatures below +5 degrees Celsius should be carried out exclusively with preliminary treatment of this very surface with a burner or heat gun. Otherwise, condensation will form on the surface, on which the paint simply will not fall;
If during painting it is cold in the room itself, then the drying time of the layer can increase several times, which is especially unpleasant for decorative painting. Therefore, it is recommended to install a heat gun and cover the surface with a film.

What are blacksmith paints

Recently, blacksmith paints, specially optimized for working with forged materials, have been very popular. Such paints are applied to forging for decorative purposes, which allows you to imitate a variety of surfaces, ranging from gold to cast iron.

The cost of such paints is higher than that of conventional ones. However, this is due to their increased shelf life, which reaches 5 years or more. At the same time, such paints also look really impressive, allowing you to give the required visual effect by the very fact of your presence. No need to apply different coloring methods.

Today there are many types of such a coating, but the German paint WS-Plast, produced by Weigel & Schmidt GmbH, is rightfully considered the most popular. These paints allow you to give the metal surface a variety of different colors and textures. Here you have an emerald color, and graphite distinguished by red tones, and various types of antique coloring. At the same time, such a coating not only decorates, but also protects the metal surface from corrosion and other troubles caused by the influence of nature.

Also popular is hammer paint (Hammerite), which is currently becoming more and more in demand. The reason is that such a paint does not require a primer, and can even be used directly on surfaces damaged by corrosive processes. However, if the rust is loose, then it still has to be removed. The surface treated with this coating becomes monochromatic with the effect of irregularly shaped patterns and aluminum flakes.

The application of this paint is mainly practiced with ferrous metals such as steel and cast iron. However, some non-ferrous metals can also be processed with it.

How to show patina

Patina is a characteristic greenish coating that appears on the surface of copper and bronze products after oxidation. At the moment, the best way to show this effect is WS-Patina paint. Thus, it is possible to age the metal and give it a characteristic respectable shine.

Antique painting

One of the most popular ways to paint ferrous metal is the effect of antiquity. In this case, several coating options are applied to the metal surface in a certain order. But first, the metal itself must be prepared properly. It is necessarily cleaned of corrosion, subjected to grinding, dirt and grease are removed. Only being sure of the cleanliness of the surface, you can proceed to the process, which is divided into several stages:

Using a brush, apply metallic paint to the surface. Don't be afraid to do it casually, as this only helps in the effect we are creating;
As soon as the first layer is completely dry, it is necessary to apply a craquelure primer. The latter allows you to get a layer of transparent film made from polymers;
The craquelure coating is applied after the primer layer has dried, which allows you to get characteristic cracks, similar to those that appear on things that have been used for decades and even centuries.

Important! Instead of a craquelure composition, the effect of antiquity can be achieved by applying burnt umber to the paint. In this case, it is best to work with a dry cloth, and remove the residue after the paint layer has dried.

Bronze metal finish

Bronze coating is one of the most spectacular visually. Therefore, often people seek to recreate it. And there are several ways to do this, and they all involve the use of bronze paint.

First of all, the surface is prepared. Cleaned from dirt, grease and rust. After that, a layer of primer for metal is applied to it, which will increase the adhesion of the layers applied above. At the third stage, bronze metallic paint is applied in 2-3 layers.

If you want to give this bronze layer the effect of antiquity, then the recesses must be treated with a patina, which allows you to get the effect of darkening with time. After that, glazing is carried out, during which we pass over the protruding elements and those places that are characterized by scuffs, with white paint. After the latter has dried, a transparent varnish is applied to fix the effect.

Conclusion

Painting under all other types of metals takes place in a similar way. Modern metallic paints allow you to create the effect of brass, copper, silver, gold and other metals.

Do not be afraid that you will fail, Practice shows that such metal processing methods are feasible without any serious knowledge. The video tutorial below will give you comprehensive information about this.

Metal products are subject to the influence of the external environment and especially humidity. You can protect the metal with the help of special anti-corrosion coatings (for example, covering the surface with zinc), as well as painting. The paint performs not only the role of a protector against corrosion, but also gives the surface a more aesthetic appearance.

Decorative painting of metal allows you to imitate a wide variety of effects. For example, you can decorate the surface in bronze, silver, or give the metal an aged noble look. How to choose a paint and varnish material, prepare the base and apply paint to it, will be discussed below.

Surface preparation

First of all, you need to evaluate the strength of the old coating. Masking tape will help with this: we make cuts on the old paint and glue the tape on these places. Then, with a sharp movement, tear off the tape. If a significant amount of paint separates after the tape, then the surface is not strong enough. If the layer is strong, then it is not necessary to remove it, it is only necessary to clean the metal from dirt, traces of rust and dust.

Note! If we are talking about heating batteries, the old paint must be removed, because. in this case, each additional layer reduces the heat output.

Surface cleaning (metal, walls, etc.) can be carried out in one of three ways:

mechanical (using abrasives or tools);
chemical (using alkaline compounds or active solvents);
thermal (using a hot air gun or an oxy-acetylene torch).

Padding

Surface treatment with a primer is necessary to create a reliable bond between metal and paint. Primers are produced on the basis of synthetic or natural film-forming substances (organic resins, drying oils, etc.).

An important property of primers is to reduce the likelihood of corrosion. Depending on the type of primer composition, the mechanisms for providing anti-corrosion protection differ.

There are several types of primers according to the nature of anti-corrosion properties:

Insulating. Such primers do not allow moisture to get on the protected metal.
Passivating. The action of passivating compositions is based on a decrease in the electrochemical activity of the material.
Protective. Such primers contain highly dispersed metal powders, in which the electrode potential is lower than that of the protected metal. This provides protection against corrosion.
Phosphating. The phosphate coating protects the metal from corrosion.
inhibitory. An inhibitor is a substance that slows down the rate of chemical reactions. Since rust formation is the result of a chemical reaction, inhibitory primers reduce the rate of development of corrosion processes.
Rust converters. Rust converters transform iron oxide into an insoluble compound.

The primer composition is applied with a brush, roller, swab or spray gun. The primer layer should not be too thick - thinner than subsequent coats of paint. The optimal thickness of the primer layer is up to 0.1 mm.

If the primed surface is matte, it must be carefully cleaned with fine-grained sandpaper. This will improve the quality of adhesion with the paintwork material.

Puttying is necessary to eliminate defects, such as cracks, as well as to level the surface. A putty composition is a mixture that includes a filler (chalk), a plasticizer, a binder, and special additives.

Application of various putties

Putty mixes are sold in one of two states - dry (diluted in water) and ready-to-use (diluted in a solvent). Putty is applied and spread over the surface with a spatula.

The choice of paint for metal

For painting metal surfaces, solvent-based paints and varnishes are most often used. Such solutions are a mixture of synthetic resins of alkyd origin and organic solvents. As the latter, white spirit or styrene is most often used.

After drying, alkyd compositions appear thick, durable, transparent, almost colorless films. Such films are resistant to all kinds of chemicals, as well as to moisture. Due to the latest quality, alkyds are widely used not only indoors, but also outside buildings.

However, when choosing a composition, attention should be paid to the recommended purpose of the paint. For example, for coloring batteries, special compositions are produced that are distinguished by high thermal conductivity and at the same time do not reduce the heat transfer of equipment.

For a long time, coloring was not applied to forged metal. There was a generally accepted opinion that the paint eliminates the advantage of handwork, hides the natural texture of the material.

However, not so long ago, paints and varnishes for forged products appeared, which allow you to artificially age the material, create the appearance of a patina, or achieve other visual effects. Also, blacksmith's paints protect the metal from corrosive processes.

The main drawback is their cost. Like the creation of forged products, specialized paints cannot be called cheap.

Metal coloring

You can apply the paint with a brush, roller or spray gun. The number of necessary layers during painting is set by the manufacturer and depends on the hiding power of the paint. Hiding power is the ability of a paintwork material to hide the color of the treated surface. The hiding power is inversely proportional to the transparency of the paintwork material, that is, the more transparent the paint, the more it will be needed.

Note! Hiding power is indicated on the packaging with paint and is determined in terms of material consumption per square meter.

Difficulties may arise when calculating the required amount of paintwork material. Manufacturing companies provide information on consumption per square meter. When it comes to painting flat surfaces, it is not difficult to calculate the consumption. However, one often has to deal with uneven surfaces - gratings, fences, curly details, etc. In such cases, when calculating, you will have to proceed from your own experience or the advice of the seller.

Surface decoration in bronze has been used for a long time. However, until recently, such paints were made on the basis of organic matter. Thus, the scope of use of such paints and varnishes was significantly narrowed due to the unpleasant odor characteristic of organic solvents. In addition, such surfaces are not resistant to temperature extremes.

To date, the most popular paints based on water and acrylic. Such compounds are distinguished by safety, ease of use, resistance to high and low temperatures, as well as anti-corrosion resistance.

There are two ways to decorate a bronze surface. Below are two step by step instructions.

The first option is monochromatic coloring:

We remove dirt and traces of rust from the surface. We are degreasing.
We prime the surface. This will improve the adhesive qualities of the materials and, in addition, will create a layer of polymer that will protect the surface from corrosion.
When the primer dries, apply 2-3 coats. Moreover, each layer can be applied only after the previous one has dried.

The second option is aged bronze:

We carry out preparatory activities in the same way as described in the first case. Then we primed the metal and painted it bronze.
The recesses on the surface are treated with a patina. It can be translucent - this will allow you to control the level of dimming.
When the paint dries, take a dry brush and glaze. To do this, apply light paint to the corners and ledges in such a way as to create a scuffed effect.
After the layer has dried, apply a transparent varnish to the metal.

You can give the metal an aged look in another way, using a craquelure primer and paint.

Instruction:

We clean the metal from dirt, traces of rust and grease.
We cover the cleaned and dry surface with paintwork material. We use a brush for coloring, since an uneven coating in this case is only beneficial.
When the paint is completely dry, apply a craquelure primer. This composition can be purchased at a hardware store. After drying, a transparent polymer film will appear on the surface.
We create the main craquelure coating. The result of the work is aged metal with traces of rust. Moreover, small cracks - craquelures - will appear on the surface.

Coloring and low temperatures

Recommends painting surfaces at positive temperatures. It is believed that the minimum allowable temperature is 5 degrees above zero. However, there are situations when you need to paint the surface urgently, despite the thermometer. And in this case, high-quality staining is possible if you follow a number of recommendations, which will be discussed below:

We clean the surface from ice, dust, dirt, rust and condensation. Moreover, standard cleaning procedures - mechanically - in this case will not be enough. Even if there is very little condensation left, all further efforts will not allow you to create a quality coating. To dry the surface well, use a burner (on gas or gasoline) or a heat gun.
At low temperatures, the paint will dry 2-3 times longer. Based on this, it is necessary to protect the painted surface from the effects of the external environment. For this, a plastic film and a heat gun are suitable.

Equally important for painting at low temperatures is to choose the right paint. Jelly-like alkyd enamels are considered the best option. Such compositions are characterized by high adhesive qualities.