DIY for hot burnishing of metals

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DIY for hot burnishing of metals

The black or opaque effect on the metal in addition to the increase in surface resistance to corrosion is also an aesthetic value that is often used on knife blades.

It is a personal taste but in recent years many makers have tried to darken their blades both at the artisanal and industrial level.

Burnishing(sometimes also called bronze or metallochromy ) is the surface coloration of a metal practiced by various methods and intended to provide protection against oxidation as well as to improve its appearance.

Usually this process can take place in two ways, burning to:

  • Cold or Chemistry (with commercially sold products such as The Ballsitol Brunitore Kit),
  • or Hot.

In this post we go to see how to make hot burner home made or DIY.


Caustic soda: sodium hydroxide, NaOH chemical formula, you buy at the supermarket as caustic soda.

It should be handled with gloves and glasses because it is caustic, dissolved in water develops heat.Caustic Soda

Potassium nitrate: or potassium nitrate chemical formula KNO3, you buy to the agricultural consortium, it is a fertilizer is certainly sold in bags of 50 kg, or in the enlargements of food products in kilo bags.

There are no particular risks in handling it.

Potassium Nitrato

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The official recipe consists of:

  • 1000 grams of water
  • 500 grams of soda
  • 300 grams of nitrate

DIY procedure for hot metal burner

Take a stainless steel container and pour in in the following order:

      1. Water
      2. Soda
      3. Nitrate.

Put the container on an electric or gas stove and bring to a boil by shaking/stirring occasionally to facilitate the dissolution of the products.

The solution so ready you have to boil it between 135 and 145 degrees , if you have a thermometer that allows you to measure the temperature is better.

Ps. Consider that the temperature is over 100 degrees Celsius because it’s not just water.

Some notes and tips for hot burning metals

  • Using the thermometer is important because if you do not reach those temperatures (around 140 degrees Celsius) the risk is that you do not get a burnished, dark color, but a color that tends to yellow.
  • Example the operation of preparation of the piece is important and the more you brush it (shiny) and the more fat it is the better for the final result;
  • Seemingly strange colors always have causes,
  • As for the colors:
    • the changing colors tending to blue are due to temperatures below 140/145 degrees
    • while the reddish or sometimes yellowish colors are due to the concentration of the solution that “defies” water and then the piece “oxidizes” quickly or in jargon they say it burns (rusts).
  • Moving on to the final stage of the burnishing operation, once you remove the piece from the bath, you have to wash it for a few seconds in clean water to purify it from the solution, then wet it with a sponge or soak it with emulsifying oil that precisely emulsifying with the watery tracks on the piece ensures lubrication avoiding oxidation.

Ps. The emulsive oil you can buy in specialized shops and hardware for millers and turners (it is used for tool cooling) and takes on a milky coloring. It costs little: about 5/6 euros per liter.


Handle the pieces with rubber gloves so that your hands do not leave traces of grease on the piece.

Degrease the pieces to be browned with professional degreasers such as fulcrum or alternatively detergents for dishes but better the fulcron.

If you really want to do things right, give it a pass in hydrochloric acid (muriatic acid).

Now the pieces or the piece should be degreased.



Diving of the pieces to be burnished

Soak the pieces in the boiling solution by holding them tied with an iron thread, better if thread is stainless steel because stainless steel can not be burnished.

Let the pieces boil inside for 20-30 minutes by checking them from time to time to see if the color achieved is what you want.

During the process the water evaporates, so it is necessary but doing VERY WARNING restore with a ladle the water that evaporates.

Be very careful, because diluting the solution lowers the boiling point and then the mixture tends to splash and that is why you have to use the ladle with a long handle and that allows you to keep a certain distance.

After the process of burning hot metals:

  • pull out the pieces,
  • wash them in running water. Consider that to neutralize the effect of acid you have to dip it (just for a short time) in a solution of water and bicarbonate being basic cancels out or even in a solution of caustic soda but here you have to be more careful so I recommend you with water and bicarbonate .
  • clean the pieces by scratching them with an abrasive sponge (the classic yellow and green kitchen),
  • dries the pieces and
  • Olia for good pieces,

Let the pieces rest for a couple of days in a lightly oiled rag.

The surface protection of burnishing

Burnishing is a process that serves to protect from rust all steels(excluding stainless steels that can not be browned).

It is a process that is routinely used on weapons, rifle barrels, barrel, shutter, etc.

Such protection is certainly not comparable to a galvanizing or a chrome …

The protection layer of some micron is formed by iron oxides, (hematite) that protect, passively the lower layers.

Aesthetically the matte black or black burnished has on the blade an aesthetic result that is truly eye-catching.

Burnished pieces should always be kept slightly oiled.

The burnishing made with this system is from the point of view of protection certainly better than the many cold burners that are found on the market.

The solution could also be reusable but should be put in containers suitable for chemicals.


  • Always pay close attention
  • He always wears glasses and gloves.
  • The solution is dangerous for the temperature of use of 140 degrees Celsius and for the presence inside the caustic soda that is highly burnt.
  • In case of accidental contact with the solution wash the part in the water abundantly and if necessary go to an emergency room.
  • To dispose of the burnishing solution once cooled you need to dilute it with plenty of water before throwing it away.Hot metal burn


Like everything if you know someone or company that performs burns professionally is a correct choice because without good equipment it is not easy to have a professional quality level.

The galvanic method for burning metals is one of several professional methods that are widely used today, even at the industrial level. This method consists of dipping the piece to be treated in a watery solution of sodium sulfate (or “Schlippe salt”), of sodium carbonate anidro and then practicing electrolysis for a few minutes at room temperature with a current of 0.35 (A) at voltages between 2.4 and 4 volts (V). This method is also used in the treatment of copper and brass.

So my advice regarding the specific case of the hot burner of metals is to test simple details such as screws or bolts, or some waste of hardened steel to be able to see the result without wasting time and Material.

After that it is also important to check that the burn is stable and with the right “depth” to make sure that it is uniform and stable on the material and does not go away with a slight abrasion.

Personally doing things at home is a personal pleasure but remember that the comparison you have to do with the same object or similar made by a professional.

If you don’t reach a certain level of quality, it means you still need to improve your achievement process.

You can also try the cold burnishing process of the ballistol or Birchwood Casey.

Hot metal burn



It is chemical burnishing but it has excellent quality levels to be done with this method.

Much used in the weapons industry but not only but I think the best thing is to test an old knife or a “wrong” knife before you do it directly on your favorite blade.

Are you experience?


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132 shares, 132 points
Andrea F

Maker and Enthusiast of Knifemaking. Other: Engineer / Professional Blogger / Bass Player / Instructor of Boxing / Muay Thai / Brazilian Jiu Jitsu / Grappling / CSW / MMA / Self Defence / FMA / Dirty Boxing / Silat / Jeet Kune Do & Kali / Fencing Knife / Stick Fighting / Weapons / Firearms. Street Fight Mentality & Fight Sport! State Of Love And Trust!


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