Why Do Blacksmiths Use Borax?

In the blacksmithing trade, there are a variety of practices and methods used and required in order to produce good-quality forged metals. One particular practice that many wonders about is the use of borax in the process of forge welding and blacksmithing.

Blacksmiths use borax as a flux, which is an agent that cleans and purifies the metal being joined in the forge welding process. This enables a high-quality weld.

Why Do Blacksmiths Use Borax?

The following information in this article will explain what a forge welding flux is, why it is required when welding, and why borax is so highly regarded as an ideal flux for this practice.

There is also a video at the end of this article that will show you how to use it and how to “cook it” properly.

* This article may contain affiliate links. As an Amazon Associate, I earn from qualifying purchases. Read my full disclosure here. 

What Is a Forge Welding Flux?

Flux is a chemical cleaning and purifying agent. In the case of welding, it is used to prevent oxidation on the base and work materials.

The basic role of flux is to dissolve the oxides present on the metal surface and act as a barrier to oxygen by coating the hot surface, which will prevent oxidation.

So then, how does the borax factor into this process? In order to understand that, we need to look at the materials in borax and how they affect oxidation.

How Borax Works As A Flux?

When borax is used as a flux, it is mixed with ammonium chloride, an inorganic compound that is highly soluble in water. The ammonium chloride works specifically as the cleaning agent, such as for cleaning the tip of a soldering iron (Amazon link).

The flux from borax promotes deep penetration in the filler metal of the joints, which causes the resulting bond to have high strength.

A benefit of using borax is that it removes oxides without bubbling up, therefore leaving less room for dust, grit, and other impurities to gather in the joints of your weld.

Anhydrous borax (Amazon link), in particular, is the best type to use for this process, as it stays where it is placed on the steel.

The use of anhydrous borax also makes the process much faster, as it liquefies earlier than regular borax.

This enables you to skip the steaming phase of forge welding, which is generally necessary when using regular borax.

By using an anhydrous option, you will end up with less scale in your welded piece, and you will not have to use as much borax as you normally would.

It is, of course, reasonable to ask if borax is the end-all-be-all to the forge welding process. To answer that, we need to look into the other resources for a flux, as well as the necessity of using flux in general.

Do Blacksmiths Have To Use Borax As A Flux?

It is clear that borax is an ideal choice for a flux during welding. However, it is not necessarily the only option for a flux.

There are a couple of alternative methods that have proven useful in the blacksmith community and are reasonable to consider before choosing borax as your main flux.

Borax Substitutes For Forge Welding

Borax isn’t the only choice of a flux. Here are a few alternatives you should consider:

Kerosene As Flux

Unlike borax, kerosene is used when the metal is still cold. If you dip the metal in the kerosene first thing, you don’t have to use it later. During forging, the kerosene will burn off and will leave an oily residue that will turn to carbon.

This will prevent the metal from oxidation and may slightly raise the carbon content of the steel. However, kerosene is highly flammable and is liable to flare up. Therefore, unlike borax, you cannot dip red hot steel into kerosene.

Brake Cleaner Flux

This substance is used exactly like kerosene. However, it is not necessarily an improvement over either kerosene or borax. This is due to the fact that brake cleaner contains additives that can become poisonous, so it is vital to exercise caution during use.

Clearly, it is not necessary to use only borax as a flux, as there are other options that prove just as useful. However, it is clear that borax is the safest option for working with heat, and has been proven to be a highly useful substance in most cases.

Many blacksmiths have foregone the use of borax entirely, even going so far as to use no flux whatsoever. This is referred to as no-flux welding, which I’ll discuss in more depth below.

Can You Forge Weld Without Flux?

In many cases, it is quite necessary to use flux when welding. However, there are some situations where it is not required, and may perhaps cause difficulties when working with hot metal.

For example, when borax heats up, it forms into a glass-like substance that will settle onto the bottom of your forge. Depending on what type of forge you have, this could prove an issue. If you work with a coke or coal forge, this should not cause much of a problem.

However, if your forge is powered by propane, this could cause the base of your forge to erode.

Because of this, non-flux forging has become more and more popular over the years. TIG welding, or tungsten inert gas welding, allows you to make precise welds without the use of a third party stabilizer such as borax.

These types of forges have become more accessible in recent years, and are considered just as good as forges that require the use of flux.

However, though this method of forging may prove convenient, it is not difficult to protect a regular forge base from the corrosion of borax.

Any of the following options are viable for this extra layer of protection:

  • Use kiln shelving. This is useful for a smaller forge, as the shelving is quite thin. It is affordable and ultimately will protect the surface from corrosion.
  • Place the metal on top of a thermal insulation board. These are generally used in fireplaces and are therefore a viable option for preventing corrosive materials.
  • Placing a junk steel plate under your workspace. Though this is the lesser of the three options, it will nonetheless keep your space safe.

The bottom line is that non-flux welding, while a viable option, is not necessarily the better choice over traditional welding with flux. Though you may have to take some extra precaution in preparation before beginning your weld, the use of borax flux is overall a safe and well-proven material for forge welding.

Furthermore, welds made with TIG or other similar forges are still at risk of welding at a low quality, and some blacksmiths recommend using borax anyway in order to guarantee a proper weld.


Borax is used as a flux when forge welding to prevent oxidation of your surface and weld.

The best type of borax to use is generally anhydrous borax (Amazon affiliate link), as it speeds up the process due to its early liquefaction, and leaves little room for impurities to get inside the joints in your weld.

Though there are some alternative materials that can be used as a flux (such as kerosene), borax is the safest and simplest material to use as a flux. A blacksmith does not necessarily have to use a flux while welding, especially depending on which type of forge they possess.

However, the use of borax offers a higher guarantee of a high-quality weld, whereas non-flux forging is more of a risk. Therefore, the use of borax in forge-welding is a safe and viable tool in order to get the best results from your welding projects.

I hope this article was informative enough! Thank you for reading and good luck with your future projects!

Cheers, tools owners!

Hi there! My name is Jack and I write for ToolsOwner. I have a passion for everything related to tools and DIY projects around the house. You often find me in my workshop working on new projects.