2% Thoriated Tungsten (Red): The DC Welding Standard

2% thoriated tungsten (red band) has been the default TIG electrode for DC welding since the 1960s. It starts easier, holds a point longer, and carries more current than pure tungsten. Every pipe welder, stainless fabricator, and steel TIG welder in the industry learned on thoriated tungsten, and it’s still the most commonly used type worldwide. The red band on the end identifies it as AWS EWTh-2, containing 1.7-2.2% thorium oxide (ThO2) by weight.

The thorium oxide raises the electron emission rate of the tungsten, which means the arc starts at lower voltage, runs more stable at low current, and erodes the tip more slowly than pure tungsten. These performance advantages have kept thoriated tungsten dominant for decades despite the radioactivity concern.

AWS Classification

2% thoriated tungsten is classified under AWS A5.12/A5.12M:

• EW = Electrode, tungsten
• Th = Thorium oxide additive
• 2 = Approximately 2% oxide content

Amperage Capacity

Stock 1/16", 3/32", and 1/8" to cover the full range of shop work. The 3/32" diameter handles the widest amperage spread and is the single best all-around choice if you only want to buy one size.

Arc Starting Performance

Thoriated tungsten is the benchmark for DC arc starting. The thorium oxide in the tungsten lowers the work function (the energy needed to emit electrons from the surface), which means the arc initiates at lower voltage and with less delay.

High-frequency start: The arc strikes almost instantly with a crisp snap. No hesitation, no wandering. This is the behavior pipe welders and production TIG welders depend on for consistent root passes.

Lift-arc start: Thoriated tungsten also excels with lift-arc (touch-start) because the low work function allows the arc to transfer cleanly as you lift the tungsten off the workpiece. Less sticking, less contamination.

Scratch start: Even the crude scratch-start method works well with thoriated tungsten, though it’s not recommended because of the contamination risk to the tungsten tip.

Grinding Characteristics

Thoriated tungsten grinds easily and holds a sharp point. The thorium oxide particles are distributed throughout the tungsten matrix and don’t cause the electrode to chip or crumble during grinding like some other oxide types can at larger diameters.

Grinding procedure:

1. Use a dedicated diamond or silicon carbide wheel (never one used for steel)
2. Grind lengthwise along the electrode, not across it
3. Grind to a point with an included angle of 20-30 degrees for general DC work
4. The ground surface should show straight longitudinal lines, not circular scratches
5. Some welders leave a tiny flat (about 0.010-0.020") on the tip to extend tip life

Point geometry affects arc behavior:

• Sharp point (15-20 degrees): Focused, narrow arc for thin material and precision work
• Standard point (25-30 degrees): Good balance of focus and current capacity for general use
• Blunt point (40-60 degrees): Handles higher amperage without melting back, wider arc cone

The Radioactivity Question

This is the topic every discussion about thoriated tungsten eventually reaches. Here are the facts:

What thorium-232 does: It’s a naturally occurring radioactive isotope that decays by alpha emission. Alpha particles are heavy, slow, and stopped by a sheet of paper, clothing, or the dead outer layer of skin. External exposure from holding a thoriated tungsten electrode is essentially zero risk.

Where the real hazard exists: Grinding. When you grind a thoriated tungsten to a point, the grinding dust contains tiny particles of radioactive thorium oxide. If you inhale this dust, it deposits in your lungs. If you ingest it (hand-to-mouth transfer in a dusty shop), it enters your digestive system. Inside the body, alpha radiation is highly damaging to surrounding tissue.

Quantifying the risk: A 2005 study by the American Welding Society concluded that the radiation dose from normal grinding of thoriated tungsten is well below occupational exposure limits. However, the dose is not zero, and cumulative lifetime exposure from daily grinding in a production environment adds up.

Risk mitigation if you use thoriated tungsten:

• Grind with a dedicated tungsten grinder that has dust collection
• If grinding on an open bench grinder, work in a well-ventilated area and wear a P100 respirator
• Don’t eat, drink, or touch your face while handling ground tungsten
• Wash hands after grinding
• Don’t dispose of ground tungsten dust in regular trash; check local regulations

The alternative: 2% lanthanated tungsten matches thoriated performance on DC, works on AC too, and contains zero radioactive material. It’s a direct replacement with no performance penalty. Many shops have switched entirely to lanthanated, and some countries (particularly in the EU) have restricted thoriated tungsten use.

DC Performance

Thoriated tungsten is optimized for DC welding. On DCEN (the standard TIG polarity), the thorium oxide helps electron emission from the tungsten surface, producing these characteristics:

Arc stability: The arc column is steady and focused, with minimal wander or flutter. This produces consistent penetration and narrow heat-affected zones on precision work.

Current capacity: 2% thoriated tungsten handles about 10-15% more current than pure tungsten of the same diameter before the tip begins to erode or melt. This means you can run a smaller tungsten at higher amperage, which is useful when you need a focused arc at high heat input.

Tip retention: The pointed tip holds its geometry longer than pure tungsten. In production welding where the arc runs continuously for minutes at a time, thoriated tungsten needs re-grinding less often.

Low-amperage performance: Thoriated tungsten starts and runs cleanly at very low currents (under 20A), making it suitable for thin sheet metal, foil welding, and micro-TIG applications.

AC Performance (Limited)

Thoriated tungsten isn’t the first choice for AC welding (aluminum), but it works in specific situations:

On inverter TIG machines with AC balance control: Adjusting the balance toward more electrode-negative time (70% EN or more) reduces the thermal load on the tungsten tip and allows thoriated tungsten to maintain a pointed profile on AC. This is useful for welders who want one tungsten type for both steel and occasional aluminum work.

On transformer machines with fixed AC balance: Thoriated tungsten erodes faster because the 50/50 balance puts too much energy into the electrode-positive half-cycle. The tip balls up unevenly and erodes, contaminating the weld. Use lanthanated or pure tungsten on these machines.

The practical answer: If you weld aluminum regularly, stock lanthanated tungsten for AC work. If you TIG weld steel 90% of the time and do occasional aluminum, thoriated tungsten on an inverter with adjustable AC balance is an acceptable compromise.

Shelf Life and Degradation

Thoriated tungsten doesn’t degrade over time in normal storage. The radioactive half-life of thorium-232 is 14 billion years, so the oxide content doesn’t change meaningfully in any human timeframe. Tungsten electrodes stored properly (dry, in their original packaging) perform identically whether they’re one month or ten years old.

Physical damage is the only storage concern. Don’t drop tungsten electrodes on hard floors (they can chip or crack), and don’t store them loose in a toolbox where they bang against each other. Small cracks or chips in the electrode can cause the tip to break off during welding, contaminating the weld and creating an inclusion.

Common Diameters to Stock

For a typical shop doing DC TIG welding on steel and stainless:

• 1/16" (1.6 mm): Sheet metal, thin tubing, orbital welding, low-amperage precision work up to 90A
• 3/32" (2.4 mm): The workhorse. Covers 60-160A and handles everything from light fabrication to moderate pipe work
• 1/8" (3.2 mm): Heavy plate, pipe fill passes, high-amperage production up to 250A

Buy 7-inch lengths for torch bodies with standard collets. The 7-inch tungsten gives you several grinds before the electrode gets too short to use.

Contamination and Recovery

Tungsten contamination happens when the electrode tip contacts the weld pool, the filler rod, or the base metal. The tungsten picks up base metal (steel, aluminum, etc.) on its tip, and the contaminated tip produces an erratic, unfocused arc.

Identifying contamination: The tip looks balled, irregular, or discolored (silver/gray instead of the normal dark gray of clean tungsten). The arc wanders instead of holding a focused position.

Recovery: Break off the contaminated section with pliers, then re-grind to a clean point. You’ll lose 1/4 to 1/2 inch of tungsten per contamination event. If the contamination is minor (just surface discoloration), grinding past it restores full performance.

Prevention: Keep the filler rod tip within the gas envelope but away from the tungsten. Don’t touch the tungsten to the workpiece on scratch-start machines (use lift-arc or HF start instead). On aluminum AC welding, the balled tip is normal and doesn’t indicate contamination unless the ball is irregular or has metallic deposits on it.

Dedicated grinding: Always grind thoriated tungsten on a diamond wheel that isn’t used for steel or other metals. Cross-contamination from steel particles on the grinding wheel transfers to the tungsten surface and contaminates the next weld.

For the non-radioactive alternative, see the 2% lanthanated tungsten guide. For a detailed comparison with ceriated tungsten, check the ceriated vs thoriated guide. For the complete tungsten electrode overview, see the tungsten electrodes selection guide.