The most common powder used in forging is borax, a white crystalline substance that blacksmiths sprinkle onto hot steel to prevent oxidation and allow two pieces of metal to weld together cleanly. But borax isn’t the only powder you’ll encounter in a forge. Depending on the type of work, smiths also use boric acid, commercial flux blends, anti-scale coatings, and even powdered steel alloys for pattern-welded (Damascus) steel.
Borax: The Most Common Forging Powder
Anhydrous borax, a form of sodium borate with its moisture removed, is the go-to powder for forge welding. When you heat two pieces of steel and hammer them together, the surfaces instantly form a layer of iron oxide (scale) that prevents a clean bond. Borax solves this problem in two ways: it dissolves the oxide layer already on the metal, and it melts into a glassy coating that seals the surface from oxygen, stopping new oxide from forming.
Blacksmiths typically apply borax when the steel reaches a red heat, around 1,800°F. At that temperature, the powder melts on contact and flows across the surface, creating a protective barrier. As the steel is brought up to welding temperature and hammered, the molten borax carries dissolved oxides out of the joint, letting the clean metal surfaces fuse together.
Boric Acid and Commercial Flux Blends
Boric acid (hydrogen borate) is another standalone cleaning agent used in forge welding. It works similarly to borax, dissolving oxides and shielding the metal from oxygen, and some smiths prefer it for certain applications. You can find it at most blacksmithing suppliers sold by the pound.
Many smiths use commercial flux blends that combine borax and boric acid with other ingredients. Some blends include iron filings, which melt at the joint and help fill tiny gaps between the welding surfaces. Others add silica sand for higher-temperature work. The choice depends on the type of steel, the complexity of the weld, and personal preference. Plain anhydrous borax remains the most popular option for general forge welding because it’s inexpensive, widely available, and effective across a broad range of steel types.
Anti-Scale Coatings for Heat Treating
A different category of forging powder is the anti-scale compound, used primarily during heat treating rather than welding. When a bladesmith heats a finished blade to harden it, scale forms on the surface and can ruin the finish. Anti-scale coatings, often sold as powders that get mixed into a paste, create a protective shell around the blade during the heating process. This saves hours of grinding afterward, since the smith doesn’t need to remove as much material to get back to clean steel. Bladesmiths commonly apply anti-scale compounds to the flat areas of a blade, especially around the maker’s mark or ricasso where they want to preserve fine detail.
Powdered Steel for Damascus Patterns
In a completely different application, actual metal powders play a central role in making canister Damascus steel. Traditional Damascus is made by stacking sheets or bars of two contrasting steels, welding them together, and folding them repeatedly to create layered patterns. Canister Damascus takes a different approach: fine steel powders are packed into a steel tube (the canister), sealed, and then forge-welded and shaped.
The most common powder alloys for this work are 1084 (a high-carbon steel), 4600E (a nickel-containing alloy similar to the popular 15N20 bar stock), and 1018 (a low-carbon steel). Knifemaker Ed Schempp, one of the early adopters of the technique, produced Damascus billets using combinations of 1084 and 3V powders alongside traditional 15N20 bar stock. The appeal of powder is that it creates extremely fine, intricate patterns impossible to achieve with stacked sheets. Powders of different compositions can be layered, swirled, or mixed to produce mosaic-like effects in the finished blade.
Because 1084 and 15N20 are already the standard pairing for bar-stock Damascus, the powder equivalents (1084 and 4600E) became natural choices. 4600E has a similar nickel content to 15N20, which is what creates the visible contrast between layers after etching.
Powder Metallurgy in Industrial Forging
On the industrial side, powder metallurgy is a manufacturing process where fine metal powders are pressed into a shape and then heated (sintered) until the particles bond together. The resulting parts are then sometimes forged to increase their density and strength. This approach works especially well for refractory metals like tungsten and molybdenum, which have melting points too high for conventional casting.
The advantages are practical: powder metallurgy produces near-net-shape parts that need little or no machining afterward, generates less waste than cutting from solid stock, and allows manufacturers to control the porosity of the finished piece. That porosity control is useful for products like self-lubricating bearings, where tiny internal pores hold oil. The process is used to make everything from gears and surgical implants to watch cases and air conditioner components.
Safety When Using Flux Powders
Borax and boric acid are relatively safe to handle at room temperature, but they pose real respiratory risks once heated in a forge. Inhaling borate dust or fumes can irritate your nose, throat, and lungs, causing coughing, wheezing, and shortness of breath. Repeated exposure over time can lead to chronic bronchitis.
The recommended airborne exposure limit for anhydrous borax is just 1 milligram per cubic meter of air over a 10-hour shift, which is an extremely small amount. Good ventilation is the first line of defense. If you’re forge welding regularly, a local exhaust system near the forge opening pulls fumes away before you breathe them. When cleaning up spilled flux powder, use a vacuum or wet method rather than dry sweeping, which kicks fine particles into the air. For higher-exposure situations, a P95 particulate respirator provides adequate protection.
Molten borax also spatters when steel is hammered at welding temperature. It sticks to skin and clothing and causes burns, so long sleeves, gloves, and eye protection are essential during forge welding operations.