Chemical bluing of steel at home: compositions, methods

Steel bluing is increasingly used for painting metal products. It provides reliable surface protection from rust and a decorative finish. With the chemical dyeing option, a protective shell appears on the surface. Oils and acids are used during the work process. Depending on the type of material used and the degree of heating, metal compounds acquire a natural shade.

Many people believe that this processing option is used only in factory conditions. But you can organize it yourself if you follow the sequence of actions and use suitable means.

Burnishing steel using linseed oil, machine oil or hemp oil

In the last article we talked about how to blue a gun barrel using “rusty varnish” and what you need to prepare the composition for blueing.
In this article we will introduce the reader to how to burnish steel using linseed oil, machine oil or hemp oil. Different shades of black appear when barrels and weapon parts are blued with different oils, more on this below. Burnishing steel using linseed oil, machine oil or hemp oil

When bluing, a steel product is heated to a high temperature and smeared with a special liquid. The sequence may vary. 1. Heat the product and dip it into the liquid. 2. Heat the product and smear it with a swab dipped in liquid 3. First, lubricate the product with liquid, and then put it in the oven and heat it to 250-300 degrees. For a denser coating, this can be done several times. I personally blued using options 1 and 2, but have never tried the third.

What is used as a bluing fluid. In the classic version, it is linseed oil or linseed or hemp oil. There is no fundamental difference. Flaxseed oil is obtained by prolonged heating - cooking linseed oil. This oil contains many unsaturated organic acids, due to which it oxidizes and polymerizes in air - “dries out.” Synthetic drying oil - oxol - should not be taken for these purposes.

Another fluid option is machine oil. Any mineral oil is suitable: I20, M8 motor oil, etc. You can take machine tool testing I-20. With semi-synthetic and synthetic oils, the result may not be the same; you need to check each specific oil.

The color and shade of bluing are not fundamentally different when using drying oil or mineral oil. But the properties of the coating are different. When heated, mineral oil impregnates the surface of the iron oxide layer, becomes charred, coked, and that’s it. Drying oil, in addition to charring on the surface of the steel, “dries out” due to oxidation by air and gives a denser coating that holds better and better protects against corrosion.

When I blued using the 1st method, to obtain a black color, I heated the steel product in a muffle to a temperature when the metal begins to glow barely noticeably in the dark. If the surface is matte (for example, stripped with a brush or coarse sandpaper), then you can heat it a little higher. If the surface is polished, then with higher heating a thicker layer of scale is formed, which then falls off in places (in spots). Also, if the product is polished before bluing, it must be thoroughly wiped and not touched with bare hands. Otherwise, your fingerprints will be clearly visible on the bluing.

After dipping into the liquid, wait a while, not long (depending on the thickness of the metal) and remove the still hot object. If you used mineral oil, carefully wipe off the remaining oil with paper rags; hot oil is easier to wipe off. If you used drying oil, use a cloth to remove any drops and smudges and leave the drying oil to dry. Hot drying oil will dry faster.

If heated below the glow-in-the-dark temperature, the bluing will have different colors (depending on the temperature). But I haven’t really experimented with this.

Large products are difficult to heat entirely and dip into liquid (especially if it is expensive drying oil). In this case, you can (according to the second option) heat it in parts with a blowtorch, gas and smear it with a swab dipped in drying oil or oil. You need to smear without smudges, because... the drops will boil and the surface will be uneven. True, these drops can be cleaned off. With this method, drying oil gives better results than mineral oil.

Source

Blackening

We will present another option on how to burnish steel with your own hands. This option is as simple as possible to use. It is suitable even for those who live in an apartment or simply do not want to carry out such a procedure with heating an alkaline or acidic liquid composition. This is bluing with a brush. Special products are sold, for example, the domestic “Raven 3” or the foreign “Prague Oxide”.

The technology is very simple to apply - you first need to remove the top fatty layer, that is, degrease the surface. But there are some disadvantages:

It is difficult to provide a good film in areas where access is difficult. Therefore, it is better to immerse crafts with complex configurations completely in containers.
The layer is not very durable and is not resistant to mechanical damage.

How to blacken metal at home - do-it-yourself steel bluing

Blackening (bluing) of steel not only protects it from rust, but makes it look more presentable. You can blacken weapons and other metal products at home using cold bluing or a solution of citric acid; we will look at how to blacken metal with oil with your own hands.

How to blue metal? You can do the bluing yourself using available materials. In this case you will need:

Acetone.
Clean rags.
Machine oil.
Pliers.
Burner.
Thick gloves, welding suit and safety glasses.
Fire extinguisher (just in case of fire).
A metal or glass container (that you don’t mind ruining).
Open space sufficient for work.

Oxidation with citric acid

Blackening with citric acid protects against corrosion, oxide films and rust. This is an old method suitable for steel with a high carbon content. If you oxidize a knife in this way, then in the places where it will be sharpened, all the coating will come off. It is not too durable, suitable for items that are rarely used.

For this you will need:

a pack of citric acid;
hot water (90-95 degrees);
machine oil.

Pour the entire sachet of citric acid (20 g) into a stainless steel or glass container, add hot water (about 200 g) and stir thoroughly. Dip the product into the prepared mixture and leave for 50 minutes. After some time, the beginning of the reaction can be observed. Bubbles will begin to actively form around the part. They can prevent air from reaching the product, so you can periodically (every 10-15 minutes) move the knife so that they disappear from the surface.

After 50 minutes, you can remove the part; it will turn black at the end of the process. It needs to be rinsed, oiled and wiped.

Popular methods for bluing steel at home

Many people believe that this processing option is used only in factory conditions. But you can organize it yourself if you follow the sequence of actions and use suitable means.

What can you achieve with bluing?

As a result of this work, a film of iron oxide will appear on the surface. The dimensions of its thickness completely depend on the technology used. It can be 1-10 micrometers. Using the metal bluing method, you can solve the following problems:

protect the coating from corrosion, since rust does not appear on blued surfaces;
give the product a more presentable appearance.

You can obtain the required coverage in many ways. But the most popular of them are alkaline, thermal or acid bluing. Alkaline treatment is ideal for DIY work. To do this you will need water, a digital scale, sodium nitrate and sodium hydroxide. You will also need a protective mask and gloves for personal safety.

For work, use only stainless steel utensils. Steel bluing is carried out under a certain temperature regime. The solution is kept in a boiling state, which is why you need to work with it extremely carefully.

To create a durable steel coating at home, the process lasts at least 1.5 hours. Before starting blackening, the surface must be degreased with a solvent. The color of the protective film is determined by the heating time, as a result of which it will constantly change. To avoid strong differences in shades, the surface is completely immersed in the solution.

Important! After completion of processing, metal products must be thoroughly washed in a soapy solution.

Blue without heat treatment

You can achieve the desired shade of blue without heat treatment - using a special solution.

To complete the work you need 2 reagents and water:

Potassium hexacyanoferrate (red blood salt) - 2.5 g.
Iron sesquichloride - 2.5 g.
Water – 1 l.

Take 2 0.5 liter jars and dissolve each ingredient in them separately. There will be no problems with this, since water is an ideal solvent for them. After this, the solutions are mixed, and a steel part is placed into the resulting mixture. It is necessary to carefully monitor the oxidation process. When the desired shade of blue is achieved, the part is removed from the solution and dried.

2 more ways

In order to make a part dark blue, you can melt the sulfur by mixing a small amount of soot into it. The part is placed in this composition, and the process of color change is controlled.
By heating the saltpeter to more than 320°C, we will bring it to a liquid state. Further, as in the previous method.

There are many more ways to blue metal, thanks to which you can achieve a beautiful and durable color of the part, but not all of them are suitable for use at home. We tried to describe the simplest and, if possible, safe ones.

Any of the methods described above for bluing metal can cause harm to human health! You need to take safety precautions in advance, remembering that hot metal can cause thermal burns, and reagents can cause chemical burns. In addition, reagents can cause fumes poisoning. Many reagents are flammable and should not be heated, so be extremely careful and follow the instructions carefully.

Popular bluing methods

Blueing technology includes several methods, the main ones being the following:

Alkaline method. In this case, you will have to work with oxidizing agents at a temperature of 130-150 degrees. Thanks to alkaline oxidation, iron is oxidized. But you should not work with this method in a house or apartment, as an unpleasant odor is released during the work.
Acid method. In this case, the work is performed in acidic solutions using a chemical or electrochemical method. It is important to place the item in the solution for the specified time and act in accordance with the instructions.
Thermal method. This type of bluing is considered the oldest and simplest in existence. This technology involves heating steel in the open air. The procedure continues until the top layer of metal reacts chemically with oxygen. The higher the heat, the darker the part will become.

Application of rust varnish

This bluing agent is often used to obtain a smooth and even surface. It contains steel shavings, but they can be replaced with cast iron shavings. In this case, financial investments will be minimal. In this case, the workpiece must be placed in a chemical agent. The result is red or black iron oxide. This instruction, as a means for cold bluing, gives a long-lasting and effective result.

To get rid of red deposits, use a brush with fairly stiff metal bristles. As a result, only black oxide remains.

First, the metal is machined and degreased. Then the product is placed in a special composition. The bluing agent is prepared in a porcelain container. It is important to wear gloves to protect your skin. The composition is made using hydrochloric acid. It is poured in a small amount into a container. It is mixed with metal filings, nitric acid and iron rust.

Corrosion protection

This is the most important goal. This is especially true when a metal structure is used outdoors, that is, the steel is constantly exposed to oxygen and moisture. With such actively reacting substances, an oxidative process - rusting - is possible. As a result, red rust is formed. It greatly affects the strength, reducing it, and also shortens the service life. In this regard, many car enthusiasts are actively interested in how to make the surface of the metal black, and how to blue the steel elements of the car, since corrosion spoils automobile spare parts.

Using machine oil

Knife bluing can be done at home with oil. You will need the following:

500 ml machine oil;
equipment for holding the part, such as special hooks, pliers or pliers;
metal container for bluing in oil;
rags or paper napkins;
gas burner, hair dryer or gas stove.

How to do the procedure if you have a hair dryer? To do this, the part is laid out on a non-combustible surface, such as a brick. Then the hair dryer is set to high heat. The part is heated as much as possible. Then, using pincers or pliers, it is placed in the bath, completely covering the surface with oil. This will ensure an even color upon completion of the procedure. Then the part is placed on a paper napkin to absorb the oil.

When processing metal using this method, you can use linseed oil. The procedure stops as soon as the desired color is obtained. The process must be repeated 3 or 4 times. At the end of each cycle, the product becomes darker.

If you are deciding how to blue your steel, this method will not turn it black. And the surface will not be too durable. This bluing product is suitable if you need to protect a steel product from rust.

Acid treatment

Burnishing steel with acid requires high-quality preliminary preparation of the material. The surface of the product is properly treated with sandpaper, and then kept in kerosene for 15 minutes.

Procedure

After preparation, the part must be thoroughly dried.

You will need to make a solution for processing.

A liter of water is poured into the container, then 2 grams of tannic acid and the same amount of tartaric acid are added.
The components are mixed thoroughly.
The mixture is heated to 140-150 degrees.

The product is immersed in a hot composition for 15-17 minutes, removed and rinsed with water. The most effective method of washing is rinsing with boiling water. Then the part is immersed in machine oil for an hour. After an hour, take it out and wipe it carefully. As a result, the product is ready for use.

Recommendations

Are you wondering how to bury metal objects yourself? To do this, you can use one of the methods that suits you. Using professional advice, you will get the perfect color of the metal, and the process itself will be carried out in a way that is safe for you.

Cold bluing involves the use of a bath or special container. But it cannot be made of any material. A wooden bath or galvanized container is optimal.

It would be good if the container was additionally equipped with hangers-hooks for placing parts in the solution. These elements can be made in the form of curved racks or mounted on a wall. Everything is determined by the height of the sides of the container and the dimensions of the workpiece.

To blue the steel, the container must be properly degreased. The best solution for this is an organic-based solvent. This can be acetone, perchlorethylene or B-70 gasoline. The base remains inert towards these compounds. But for each type of metal it is necessary to select the optimal solution. Only with its help can you obtain the optimal color and maximize the characteristics of the product.

Even if you are doing cold bluing, the work should be done outdoors or in a room with good ventilation. This is due to harmful fumes and a strong chemical odor.

If you cannot clean the surface well with a brush or abrasive, use etching. Each type of metal has its own remedy. If you have a ferrous metal product, the bluing liquid includes 100 grams of nitric, 50 grams of sulfuric and 150 grams of hydrochloric acids per 1 liter of distilled water. The surface is treated for at least 2.5 hours. Chemical polishing is used to give a smooth surface.

Thus, you can do the bluing of a steel object yourself. To do this, it is important to choose the most suitable processing method and adhere to a clear sequence of actions. As a result, you will get a corrosion-resistant surface in a suitable shade.

How to make steel blue

The technology for blueing metal is more complex and requires not only more effort, but also the presence of some equipment. We'll need a forge. It is very good if it has automatic blowing. It is clear that not everyone has a forge, so if you don’t have one, you can use an ordinary metal barrel, half filling it with chopped brushwood.

So, we have a part, now we need a metal box to fit its size.

It needs to be filled with fine birch charcoal and placed in a thoroughly heated forge (or in a barrel).
The part to be treated must be wiped with vinegar and left to dry.
You should wait until the coal in the container begins to smolder.
The workpiece is placed in the smoldering coals and left there until a slight blue color appears.
As soon as the part begins to turn blue, it needs to be pulled out and cleaned with soft charcoal.
The part is again placed in its place in the drawer and, after changing the color of blue, it is again pulled out and cleaned.
The work is repeated until the part acquires the desired color.

It is important to monitor the heating process and remove the part in time, otherwise its color will change to gray.