3 proven ways to blue a knife

Hello ladies and gentlemen. Today we’ll talk about bluing, oxidation or blackening of steel. This is a method of coating steel with a thin layer of iron oxides. It protects the metal from corrosion and also gives an attractive tint to the product. You can achieve black blue-black, gray or blue. The process takes place under the influence of chemical (alkali or acid) and thermal methods. I will show several methods that I have personally tested.

Hot bluing

Let's start with the fastest, and perhaps most effective method.

We will need:

• Machine oil.
• Degreaser.
• Bake.
• White spirit

Blade bluing process:

We will burnish the knife with temperature and oil. I used machine made, but sunflower will also work. The product that will be blued, in my case a knife, must be degreased. I used white spirit.

Next, pour the oil into a container, preferably porcelain, I poured it into a mug. We immerse the blade in the oil and place the mug in the oven at a temperature of approximately 280 degrees Celsius. A few words about the oven.Ideally, we need a muffle furnace with temperature control, but where can we get one? A kitchen oven will do, but the room should be very well ventilated. I used a cooling forge as well as a cooling stove in the house.

The second option is far from the best, since the oil begins to boil and evaporate, which is accompanied by an unpleasant smell, as well as the fumes themselves (which is why the oven is not the best cooker). You need to boil the knife like this for 10 to 20 minutes, until you are satisfied with the shade. Here's the result:

After letting the product cool, wipe it again with a degreaser and wipe dry. Of course, hardening will not go away with this method.

Burnishing in citric acid

A fairly well-known and effective method, but longer.

You will need:

• Lemon acid.
• Warm water.
• Degreaser.
• Napkins.

Burnishing process:

For 0.5 liters of water you need approximately 50 g of lemon. I poured 10 grams into a 150 ml glass. The acid should completely dissolve in water. Next, we also degrease the surface of the blade and lower it into the solution. After a couple of minutes, bubbles should form on the product.

Blackening takes from half an hour to two hours. In general, it depends on the steel, but I've tried different brands and the results are pretty much the same for all of them. Every 15 minutes, the blade must be taken out and wiped with napkins, removing black deposits. Once you are happy with the color, you can take out the knife and wipe it with vegetable oil, this will stop the reaction.

And yes, the water should be hot 70-90 degrees Celsius. Although I often set this temperature, the process proceeded unevenly.

Here are two examples that are completely different from each other.

Differences due to different grades of steel. The darker one is high-carbon (formerly a file), blackening is ideal for such brands.Well, I constantly wiped the blade. The second knife is mild steel, which I simply left in the solution for about a day, and the process was uneven. Overall, I’m still pleased with the result, the shade turned out interesting (there is a yellow tint in the photo, but in reality I notice it).

This is another file that turned gray in half an hour.

Burnishing in vinegar

You will need:

• Table vinegar 9%.
• Degreaser.

Burnishing process:

The vinegar needs to be boiled, but you can do without it. He already smells terrible, so I gave up. But the vinegar should not be cold, at least at room temperature. The blade can be washed under hot water so that it also warms up, then degrease and dip in vinegar, also cleaning it from black deposits every 15-20 minutes.

Afterwards, wipe the blade in oil.

The result is this:

All these methods allow you to oxidize the blade, which will protect it from rust and also give it an interesting tinted color. In all cases, you should not breathe in the fumes of bluing; they are harmful to health.

All these methods will allow you to achieve any result you need. The coating is quite durable in all the methods described, and it will definitely last for a couple of years. I hope the article was useful to you.