Burning metal with citric acid at home

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Blueing (otherwise oxidation, bluening, blackening) is a method of protecting low-alloy steel, as a result of which a thin (only a few microns) film of iron oxides forms on its surface. This film not only gives the steel its color (from brown to dark blue and black, depending on the thickness), but also protects it from rust. There are three main bluing methods - alkaline, thermal and acid. The first two are high-temperature, they are difficult to carry out at home. For information on how to burn a knife at home, read our article.

Content:

Work materials
- Step 1. We prepare the solution for bluing
- Step 2. We burn the blade of the knife
  - Burning a knife at home

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Materials for work

In order to to throw a knife, you will need:

knife made of carbon or low alloy steel;
capacity according to the height of the knife blade;
water;
lemon acid;
paper towels;
sunflower oil;
electric kettle.

Step 1. We prepare the solution for bluing

We heat the water to 70-80 degrees Celsius. There should be enough water to completely cover the blade of the knife inserted into the container.

Pour water into a container and add citric acid at the rate of 10 g per 100 ml of water. Stir the solution until the acid crystals are completely dissolved.

Stir the solution until the acid crystals are completely dissolved.

Step 2. We burn the blade of the knife

We place the knife blade in a solution of citric acid. If the blade is not completely submerged, add hot water.

After some time (in the example - 1.5 minutes) a strong oxidation reaction will begin.

Under no circumstances should you inhale the escaping fumes.

10 minutes after the start of the reaction, remove the knife from the solution and wipe the blade dry with paper towels.

As you can see, the blade has already darkened a little, but the resulting layer is still not enough.

Again we place the knife blade in the solution, and after ten minutes we take it out and wipe it.

Putting the knife blade back into the solution

To burnish evenly, you need to take out and dip the knife every one and a half minutes until the bubbles disappear from its surface.

A stable bluing color, indicating a sufficient layer of iron oxides, is obtained after 3-4 ten-minute cycles. The solution must be periodically heated, as it cools, the reaction will decrease, and then stop altogether.

After the end of the last cycle, we not only wipe the blade dry, but also lubricate it with sunflower oil. This will completely stop the reaction.

After complete drying, the knife blade looks like this.

The film that forms on the surface of the knife when bluing with citric acid is very stable. This is what a knife blued with this method looks like more than three years ago.