TIG Welding Gas Type: The Complete Guide to Shielding Gases

A hobbyist picks up a TIG torch, fires up an AC bead on a clean piece of aluminum, and the puddle refuses to flow — the weld comes out gray, sooty and full of pores. Nine times out of ten the problem isn’t technique; it’s the bottle. The shop had filled the cylinder with the 75/25 argon/CO2 MIG mix because it was ‘welding gas’ — and CO2 destroys TIG arcs. Choosing the right TIG welding gas type is the cheapest, fastest upgrade you will ever make to your welds, and this guide shows you exactly which gas belongs on which metal.

Why the Gas Bottle Matters as Much as Your Torch

Aluminum has a way of exposing the wrong gas quickly. A welder we’ll call Ray spent an evening dialing in his machine for a fuel tank bung: cleaned the plate with a fresh stainless brush, set the AC balance so the cleaning zone looked right, propped his hand to steady the torch. The arc started fine, but the puddle sat there dull and stubborn, refusing to wet out. The finished bead was gray, sooty along the toes, and peppered with pores when he cut it open. Nothing about his technique had changed. The bottle behind his bench had.

His supplier had swapped in a full cylinder of 75/25 argon/CO₂, the standard mix for short-circuit MIG, because it was cheaper to stock one “welding gas.” Carbon dioxide does not belong in a gas tungsten arc. It breaks apart at arc temperature, oxidizes the tungsten, and contaminates the pool. The fix cost Ray nothing but a different cylinder tag.

So here is the short answer, before anything else: for manual TIG welding, 100% argon is the default shielding gas on virtually every metal — steel, stainless, aluminum, magnesium, copper, titanium and nickel alloys alike. Everything else in this article is a refinement of that starting point, not a replacement for it.

What Shielding Gas Actually Does in GTAW

Gas tungsten arc welding uses a non-consumable tungsten electrode and an externally supplied shielding gas to protect the arc and the molten pool, as described in the AWS Welding Handbook, Chapter 3. That definition hides the important part: the gas is doing three jobs at once.

• Displacing air. Nitrogen and oxygen from the atmosphere dissolve into molten metal and come back out as porosity, brittle nitrides, and heavy oxide films.
• Stabilizing the arc. The gas becomes plasma. Its ionization potential, thermal conductivity and density decide how the arc starts, how wide it spreads, and how much heat actually reaches the puddle.
• Protecting the electrode. A clean tungsten keeps the arc focused and the start predictable. A contaminated one balls up, spits, and wanders.

Because those three jobs depend on gas chemistry rather than on the torch you bought, gas selection is a process decision with its own standards. AWS specification A5.32/A5.32M classifies welding shielding gases independently of unit systems — SG-A argon, SG-C carbon dioxide, SG-He helium, SG-H hydrogen, SG-N nitrogen, SG-O oxygen — and AWS C5.10, Recommended Practice for Gas Tungsten Arc Welding, covers those same six industrial gases and how each one affects arc characteristics and the finished weld.

The Gases This Guide Covers

Manual TIG uses a narrow slice of that classification list. Argon is the workhorse; Nippon Sanso’s shielding gas guide calls argon the closest thing to a universal TIG gas, usable on most materials and thicknesses in GTAW. Helium and argon–helium blends add heat for thick or highly conductive work. Argon–hydrogen blends add speed and color control on austenitic stainless. CO₂, oxygen and nitrogen do not belong in a GTAW shield — and section six explains exactly why beginners keep asking.

Gas or blend	Role in GTAW	Typical use
100% argon (SG-A)	Default shield and purge	All metals, manual work
Helium / Ar–He	Hotter, broader arc	Thick, conductive, mechanized
Ar–H₂ (SG-H blends)	Reducing, higher conductivity	Austenitic stainless only
CO₂ (SG-C)	Not a GTAW shield	GMAW / FCAW only

Who Needs This Information

The same gas logic applies at four different benches:

• Hobbyists and garage welders, who mostly need to avoid the wrong bottle and get flow rates right — the same audience reading our Aluminum Cleaner for Welding: How to Prep Aluminum Right guide, since cleaning and shielding solve the same gray-bead problem from two directions.
• Students learning the process, ideally alongside a structured Aluminium Welding Course: What You Learn, Costs & Careers, where gas selection is a lab prerequisite.
• Fabrication shop welders moving between manual and mechanized setups, where a blend earns or loses money every shift. Context for that world sits in our Aerospace TIG Welding: Standards, Techniques, and Training article, where shielding control is audited.
• Buyers and shop owners specifying cylinders, comparing Airgas Welding Supplies: The Complete Buyer’s Guide against local exchange options, and paying for purity they may not need.

Sections two and three build the science and then go deep on argon. Sections four and five cover the blends that add heat or speed. Section six puts the CO₂ question to rest, section seven gives you a metal-by-metal selection table, section eight maps symptoms to gas causes, and section nine handles safety and cost. By the end you should be able to walk up to a supplier counter and ask for exactly the right gas with no second guessing.

How Shielding Gas Works Inside the TIG Arc

Before you can pick a gas, it helps to understand what the gas is actually doing in the half second between the arc striking and the puddle freezing. A TIG arc runs hot enough to boil steel, and at those temperatures bare metal behaves less like a solid and more like a chemical sponge. Air is roughly 78% nitrogen and 21% oxygen, and both gases will happily dissolve into molten metal if you let them.

According to AWS C5.10/C5.10M, the standard for shielding gas for gas tungsten arc welding, gas tungsten arc welding produces high-quality, sound welds precisely because a controlled inert envelope keeps the atmosphere away from the arc and the puddle. Remove that envelope and the same torch, same operator and same settings produce porosity, oxide inclusions and brittle, contaminated weld metal.

What the Shield Keeps Out

The shield has three jobs, and each one affects a weld you can see:

• Excluding oxygen. Oxygen combines with alloying elements to form oxides. On aluminum you get a dull, crusty, sooty bead; on stainless you get heat tint and reduced corrosion resistance; on titanium you get a weld that is effectively ruined below the surface.
• Excluding nitrogen. Nitrogen dissolves into the puddle and later comes out of solution as gas pockets and nitride stringers. The result is porosity plus a hard, brittle fusion zone that cracks under load.
• Stabilizing the arc column. The gas carries current between the electrode and the work. Its density, conductivity and ionization behavior determine how focused or diffuse that column is, which in turn determines penetration shape, heat input and how easily the arc starts.

That second and third job are why shielding gas quality and cleanliness matter as much as technique. Wet gas, leaking fittings or a draft blowing across the arc reintroduce exactly what the bottle was meant to exclude. The same principle applies to joint preparation: Aluminum Cleaner for Welding: How to Prep Aluminum Right covers the surface side of the same contamination problem.

The Four Properties That Shape an Arc

Shielding gases are not interchangeable because their physical properties differ dramatically. Four properties do most of the work:

Property	Argon	Helium
Chemistry	Monatomic, inert	Monatomic, inert
Relative density (air = 1)	About 1.38 (heavier than air)	About 0.14 (much lighter than air)
Thermal conductivity	Low	High
Ionization potential	Roughly 15–16 eV	Roughly 24–25 eV
Typical arc profile	Narrow, stable, deep penetration	Wide, hot, broad penetration

The density difference explains coverage behavior. Argon being heavier than air means it settles over the puddle and needs modest flow rates, while helium is so light it rises and escapes, which is why helium service calls for higher flow, larger cups and better draft control. As The Fabricator’s guidance on choosing shielding gases puts it, gas selection is really a choice of arc character, not just a choice of inertness.

Why Helium Arcs Behave Differently

For years the simple explanation was ionization potential: argon ionizes at around 15–16 eV, helium at 24–25 eV, and higher ionization energy was said to translate into more energy in the arc. The fuller picture, presented in arc research at AWS conferences, is about heat transfer instead.

In the 8,000–10,000 K temperature band typical of welding arcs, helium’s thermal conductivity is roughly seven times greater than argon’s. A helium plasma simply moves energy outward from the arc core far more efficiently, which is what produces the wider, hotter, deeper-penetrating arc welders experience. The split of heat reaching the work reinforces the point: roughly 80% of the heat crossing the arc boundary layer to the anode is carried by electrons, with only about 20% delivered by conduction through the hot gas.

There is a further twist. Once a puddle exists, metal vapors from the weld pool enter the arc, and metal vapors ionize at around 5 eV. Because they ionize so much more easily than either argon or helium, they dominate arc conductivity near the work surface. The gas you choose sets the arc’s overall shape and heat distribution; the pool’s own vapor refines the behavior right where the weld is being made. For a broader comparison of how shielding gases behave across arc processes, Linde’s TIG welding gas overview is a useful companion read.

Understanding this science also explains why purity matters. Argon rated at 99.997% is the norm for critical work, and specs like HSE’s guidance on welding fume and process risks remind us that what comes out of the bottle is a controlled industrial product, not a generic commodity. Aerospace and code work push this further, with documented purge and flow procedures, a theme covered in Aerospace TIG Welding: Standards, Techniques, and Training. With the physics in hand, we can now look at the default gas every TIG welder starts with: pure argon.

100% Argon: The Default TIG Welding Gas

If you take one thing away from this guide, make it this: a bottle of pure argon covers roughly 90% of the TIG welding you will ever do. Steel, stainless, aluminum, copper, nickel, titanium — argon handles all of them. It is the gas every welding chart lists first, the gas your supplier keeps on the pallet, and the gas recommended by Linde’s TIG welding gas application data for manual work on essentially every common metal.

So why does one inert gas work so universally? The answer is simple physics plus one practical detail that matters more than anything else: control.

Why Argon Arc-Starts So Easily

Argon has a low ionization potential, meaning it takes relatively little energy to strip electrons from its atoms and turn it into a conductive plasma. For a manual welder that translates into two things you can feel. The arc starts cleanly and predictably, whether you run a non-contact high-frequency start or a scratch start on an older machine. And the arc voltage stays stable as your hand moves and arc length drifts, without the sputtering and popping you get from a gas that resists ionization.

The Praxair MIG and TIG blends datasheet makes exactly this point: argon’s low ionization potential produces easy arc starting and a stable arc, which is why it is the base gas for nearly every commercial TIG blend on the market. Stability sounds boring until you have fought an erratic arc for an afternoon — it is the single most valuable property argon offers.

Best Puddle Control, Especially Out of Position

Argon’s arc column is relatively narrow and cone-shaped compared with helium-enriched arcs. That focused, soft arc gives you an intimate puddle that starts exactly where the arc does and stays where you put it. Overhead, vertical-up, and tight inside corners all become easier because the puddle does not wander or slump the way a broader, hotter arc can encourage.

This is why argon remains the universal recommendation for manual GTAW, including out-of-position work, per industry application guidance. It is not the hottest gas and not the fastest. It is the most controllable, and for a human hand feeding filler rod, control beats raw heat nearly every time. If you are still building foundational skills, that control is exactly what you need — and courses like this aluminium welding course overview show how strongly TIG fundamentals rest on consistent gas shielding.

Argon Across the Common Metals

• Carbon and low-alloy steel: Clean, well-shaped beads with good starts. Fully acceptable for manual work, though the blends in the next section can speed things up.
• Stainless steel: A smooth bead with good color control on thin material. For heavier sections and brighter colors, argon/hydrogen blends earn their cost.
• Aluminum: Argon’s showcase. On AC, the reverse-bias half of the cycle blasts the aluminum oxide layer off ahead of the puddle, producing the white etched zone you want to see. No CO2-bearing gas can replicate this — CO2 destroys both the cleaning zone and the tungsten. Proper aluminum surface prep still matters, but argon does the electrochemical work at the arc.
• Copper and copper alloys: Argon welds them, though pure copper’s conductivity is exactly where helium blends start to pay off.
• Titanium, zirconium and nickel alloys: The standard shielding gas and, crucially, the standard purge and trailing gas as well. Argon’s high density keeps it put over exposed hot metal better than lighter gases.

Flow Rates and the Gas Lens Advantage

Tungsten Diameter	Standard Collet Body	Gas Lens Body
0.020 in.	5–8 CFH	3–5 CFH
1/16 in.	7–12 CFH	5–8 CFH
3/32 in.	10–15 CFH	7–10 CFH
1/8 in.	10–18 CFH	8–12 CFH
3/16 in.	20–35 CFH	12–18 CFH

A gas lens replaces the standard collet body’s restrictive bore with mesh screens that break up turbulent flow and straighten it into a laminar column. The result is a longer, calmer, more forgiving shield that lets you drop flow roughly 30–40% while getting better coverage. You can hold a longer arc, reach deeper into a joint, and use a stick-out that would starve a standard setup. If you weld aluminum or stainless in any quantity, a gas lens is the cheapest performance upgrade on your torch.

Purging and Trailing: Argon’s Second Job

On reactive metals, shielding the arc alone is not enough. Titanium and zirconium absorb oxygen and nitrogen from hot bare metal and turn brittle, sometimes invisibly. The back side of the joint gets purged with argon, and a trailing shield or drag cone keeps flowing argon over the cooling bead behind the torch. Argon’s density is why it excels here: it blankets exposed surfaces instead of drifting away. The same logic applies to the root pass on stainless pipe, where purge gas keeps the underside bright and sound.

Get this right and your welds will look professional on every metal. If aluminum is your particular focus, our related guides on aluminum MIG welding and alloy wheel repair show how shielding gas choice carries over across processes.

Argon is the default. But default does not mean optimal for every joint — and that is where helium comes in.

Helium and Argon–Helium Blends: More Heat, More Speed

Argon covers most manual TIG work comfortably. But what happens when the plate gets thick, the material sucks heat away faster than you can add it, or the production schedule demands faster travel speeds? That is where helium enters the conversation. Helium is the second-most-common TIG shielding gas, and understanding it separates “good enough” welding from genuinely efficient welding.

Why Helium Runs Hotter

Helium’s key property is thermal conductivity. The helium plasma in the arc column transfers heat to the workpiece far more efficiently than argon plasma does, which produces a hotter, broader arc cone. In practical terms you get deeper penetration, wider wetting at the toes of the weld, and higher travel speeds at the same amperage. The Praxair MIG and TIG blends datasheet states it plainly: helium’s high thermal conductivity gives higher welding speeds and deeper penetration, but arc starting and arc stability are not as good as with argon.

Helium also raises arc voltage. Published comparison data shows argon running at roughly 11–13 V, an argon/helium A-75 blend at 13–15 V, and an A-50 blend at 15–17 V at the same amperage. Higher voltage at equal current means more total power going into the puddle, which is exactly why a helium-rich arc feels so much more aggressive.

Pure Helium vs. Argon–Helium Blends

Very few operators run 100% helium by choice. It starts poorly, demands careful technique, and burns through cylinders quickly. Blends give you the best of both gases: argon’s easy, reliable arc starting and puddle control paired with helium’s heat input. Common ratios include:

• 75Ar/25He (A-25) – a mild boost. Slightly hotter arc and faster travel than pure argon, with almost no penalty in arc starting. A sensible first step for thicker aluminum or copper.
• 50Ar/50He (A-50) – noticeably more penetration and speed. Popular for mechanized TIG and for manual work on heavier non-ferrous sections.
• 25Ar/75He (A-75) – close to pure helium in heat output, but argon still stabilizes the start. Used where maximum penetration matters.

These designations come straight from shielding gas standards: the commercial names HeliStar A-25, A-50 and A-75 correspond to the ISO/ AWS classifications such as I1, TIG plus helium fractions, as set out in AWS A5.32/A5.32M. Ask your supplier for the classification rather than the brand name and you will always get a equivalent gas.

Flow Rates and Practical Trade-Offs

Helium is lighter than air and rises, so it escapes the weld zone more readily than argon. Published TIG flow charts recommend roughly double the argon flow rate when running pure helium, and proportionally higher flows as the helium fraction increases. A gas lens body helps enormously here, because it delivers a wider, slower, less turbulent column that holds coverage with less total flow.

The other costs are real:

• Harder arc starting. Helium’s higher ionization behavior makes HF initiation less consistent, especially on older machines.
• Higher gas consumption. You are paying for more volume per hour, and helium itself costs more than argon.
• Less manual control. The hotter arc moves the puddle faster. On thin material or out-of-position work, that extra heat is a liability rather than an asset.

When a Blend Earns Its Price

For manual TIG on aluminum, Linde’s TIG welding gases chart recommends pure argon as the default: best arc starting, best cleaning action, best weld quality and lowest gas consumption. Move to a 75Ar/25He blend when you need higher speed and greater penetration on heavier sections, and consider helium-rich mixes for mechanized welding of thick, highly conductive plate.

Good situations for argon/helium blends include:

1. Thick aluminum or copper joints where argon alone stalls out.
2. Mechanized or automated TIG where the arc is stable and speed matters more than operator feel.
3. Production runs where shorter arc times offset the higher gas cost.

Poor situations: thin sheet, root passes needing careful control, out-of-position work, and anyone still learning puddle management. If you are repairing an aluminum boat hull or working on a curved automotive panel where the torch angle keeps changing, argon keeps the arc predictable, which is why it remains the standard in aluminum boat welding and most alloy wheel repair.

Argon–Hydrogen Blends for Stainless Steel — and Where They Are Forbidden

Pure argon will cover almost every manual TIG job you will ever run. But there is one metal family where a small, deliberate addition of hydrogen genuinely changes the result: austenitic stainless steel. Argon–hydrogen is the specialist bottle in the rack — and it is also the one shielding gas family that will actively ruin a weld if it ends up on the wrong metal. Both sides of that coin are worth knowing before you open the valve.

What Is Actually Inside an Argon–Hydrogen Cylinder

Commercial blends are sold under names such as HydroStar H-2, H-5 and H-10, where the number tells you the percentage of hydrogen mixed into the argon. The industry splits cleanly along manual versus mechanized work:

Blend	Hydrogen content	Typical application
Ar + 2% H₂ (H-2)	Low	Manual TIG on thin 300-series stainless, root passes
Ar + 5% H₂ (H-5)	Manual upper limit	Manual fabrication where speed and bead color matter
Ar + 10% H₂ (H-10)	Mechanized range	Orbital and automated stainless welding
Ar + 15% H₂	Mechanized range	High-speed automated runs on austenitic stainless

For manual work, hydrogen additions typically stay between 2 and 5 percent; mechanized applications push that to 10 to 15 percent, as documented in the Praxair MIG and TIG blends datasheet. The reason for the split is simple: hydrogen makes the arc hotter and less forgiving. On a hand-held torch you want that extra heat without losing puddle control, so you keep the percentage low.

Why Hydrogen Makes a Stainless Puddle Behave Better

Two things happen when hydrogen joins the shield. First, hydrogen raises the thermal conductivity of the plasma, so more heat travels out of the arc and into the work. The arc runs hotter, penetration deepens and travel speed climbs. Reported increases of 10 to 25 percent in travel speed for GTAW of austenitic stainless are common once hydrogen is added to argon.

Second, hydrogen creates a reducing atmosphere around the puddle. Instead of letting oxygen grab the hot metal, the hydrogen scavenges it. The result is better wetting, cleaner bead color and a smoother contour, with less undercutting even at low current levels. That is why Linde’s TIG gases chart rates these blends highly for out-of-position and low-amperage stainless work.

The payoff shows up on jobs like food-grade stainless handrails, pharmaceutical tubing and decorative welds, where the bead has to be structurally sound and still look clean after a quick pass with a brush.

Where Argon–Hydrogen Is Strictly Forbidden

Here is the rule worth tattooing on your regulator: hydrogen-bearing gas goes on austenitic stainless and certain nickel alloys, and nothing else.

Carbon and low-alloy steels are the biggest trap. Hydrogen dissolved in a hardenable steel weld can cause delayed cracking hours after the metal has cooled, which is exactly why these blends are excluded from that work. If you are joining structural or alloy steel, stay with the consumables and gas pairings covered in Alloy Steel Welding Electrodes: Selection, Use & Safety. Aluminum and copper misbehave with hydrogen for different reasons, but the outcome is identical: porosity and a ruined bead. And if your stainless job turns out to be a repair on an aluminum part, get the prep right first with Aluminum Cleaner for Welding: How to Prep Aluminum Right, then shield it with 100 percent argon.

Back Purging and the Nitrogen Alternative

Argon–hydrogen is not just a front-side gas. On 300-series stainless pipe and heavier plate, the mix is considered an excellent back-purge gas: it keeps the root side bright, promotes full fusion and prevents the sugary oxidation you get from a bare argon purge that has leaked or run thin.

Not every stainless job wants hydrogen, though. Argon with a small nitrogen addition is another route on 300-series stainless, improving fusion and penetration while retaining stainless appearance and properties, according to Nippon Sanso’s shielding gas overview. Nitrogen also matters on duplex and lean duplex grades, where it supports the austenite balance rather than poisoning the puddle.

The short version: start every manual TIG job on 100 percent argon, reach for argon–hydrogen when the work is austenitic stainless and speed or bead color is the goal, use it as a purge gas on stainless root passes, and keep it far away from carbon steel, aluminum, copper and coated stock.

What About CO2? Why Carbon Dioxide Gas Is Not a TIG Gas

Every beginner asks it eventually, usually while staring at a half-full cylinder of MIG gas: “Can I just run this 75/25 argon/CO2 mix through my TIG torch?” The short answer is no. The longer answer shows what makes GTAW unique.

What Actually Happens When CO2 Hits a TIG Arc

Strike an arc on steel with CO2-containing gas and the trouble starts immediately. At arc temperatures, carbon dioxide does not stay intact: it dissociates into carbon monoxide and oxygen, and that free oxygen attacks two targets at once (The Fabricator). It oxidizes the molten puddle and pulls alloying elements out of it, a problem called dealloying. Then it attacks the tungsten electrode itself: the tip balls up, turns blue or purple, spits, and erodes in a fraction of the time it would last in pure argon.

The arc gives it away: erratic, wandering, hard to restart, with welds that come out gray, cloudy and porous. Nothing is wrong with your hand. You fed the arc an oxidizing gas it was never built for.

The Standards Draw a Clear Line

This is not shop superstition. AWS A5.32, the specification covering shielding gases for arc welding, classifies each gas by designation and intended behavior. Carbon dioxide is fully classified as a welding gas, SG-C, but the standard restricts CO2-containing atmospheres to arc welding processes other than GTAW (AWS A5.32/A5.32M). It accepts CO2 as a legitimate welding gas, just not a legitimate TIG shielding gas.

The reason is simple: TIG is the only common arc process with a non-consumable tungsten electrode sitting inside the arc. MIG wire melts and is replaced continuously, so a mildly oxidizing gas is tolerable. Tungsten endures the full arc, so anything oxidizing destroys the electrode and, with it, arc stability. See our aluminum MIG welding guide for how gas selection changes when the electrode is consumable.

TIG Gas vs MIG Gas: The Cheat Sheet

Process	Typical shielding gas	Why it works
GTAW, manual, any metal	100% argon	Easy arc starts, stable column, best puddle control
GTAW, thick or mechanized	Ar/He or Ar/H2 blends	More heat input and better wetting on specific metals
GMAW short-circuit on steel	75/25 Ar/CO2 or 100% CO2	Cheap, stable short arc; acceptable because wire is consumable
FCAW (gas-shielded)	100% CO2 or Ar/CO2	Flux chemistry designed for an oxidizing atmosphere
GMAW on aluminum	100% argon	Only common case where MIG and TIG share one bottle

Notice that last row. As Nippon Sanso points out, argon is the standard GTAW gas for all materials, while 100% argon in GMAW is essentially limited to aluminum and other nonferrous metals. That is why a “100% argon” bottle is the one cylinder you can safely share between your TIG and MIG on aluminum work, while every CO2-blended bottle belongs on the MIG side of the shop.

What About Oxygen and Nitrogen?

Two other gases confuse beginners. Oxygen is never used as a shielding gas at 100%. It appears only in small additions, typically 2 to 5 percent, mixed with argon for pulsed or spray-transfer GMAW on steels, where it stabilizes the arc and improves bead wetting (Nippon Sanso). Pure oxygen on a TIG arc would burn the tungsten and the puddle both. Nitrogen is not a true inert gas; at arc temperatures it reacts with many metals to form nitrides, so it has no role as a GTAW primary shield, though it sometimes appears as a backing or purge addition for specific stainless grades. For aluminum flux-core work, our aluminum flux core welding guide shows where those chemistries fit.

One safety point deserves emphasis. Carbon dioxide can displace oxygen in a workspace and lead to suffocation, and carbon monoxide can form in the arc zone itself, which is why ventilation matters even with inert gases (OSHA welding safety guidance). That risk follows the cylinder wherever it rolls.

The practical rule is simple: if the label says 75/25, 90/10, 98/2 or “C25,” it is MIG or flux-core gas. A TIG bottle says 100% argon, or a named argon/helium or argon/hydrogen blend. With that settled, the next question is which TIG gas belongs on which metal.

Matching TIG Gas to Metal: A Practical Selection Guide

Now for the part you actually came for: which bottle goes on which metal. Manual TIG welding is refreshingly simple here. For the vast majority of jobs in a hobby shop or fab bay, the answer is 100% argon, full stop. The interesting part starts when you move into thick stock, highly conductive metals, mechanized setups, or stainless that needs a cleaner, faster-moving puddle. Here is how the published selection matrices from the major gas suppliers line up, metal by metal.

A Four-Step Selection Process Before You Pick a Bottle

Before jumping to a table, it helps to run the same four-step mental checklist that Linde recommends for shielding gas selection: first identify the material type, then its thickness and cleanliness, then the welding position and transfer mode, and finally the job requirements such as travel speed, cosmetic appearance, and code or purity demands. A dirty, mill-scaled plate in the flat position and a spotless, purge-backed titanium root in an aerospace shop can be the same thickness and still call for very different gas decisions.

The Metal-by-Metal TIG Gas Chart

Metal	Thickness	Manual TIG gas	Mechanized / production	Purge needed?
Mild & low-alloy steel	All	100% argon	100% argon	Rarely; only heavy sections or critical roots
300-series stainless	Under 1/16 in.	100% argon	100% argon	Usually not on thin wall
300-series stainless	Above 1/16 in.	Argon, or Ar/H₂ H-2 or H-5 for slight oxide	95Ar/5H₂ or argon/helium blends	Yes on root passes of tube and pipe
Aluminum & magnesium	All	100% argon	Argon, or 75Ar/25He for thick	Not applicable (no oxide purge)
Copper & brass	Thin	100% argon	Argon/helium	No
Copper	Thick / highly conductive	Argon/helium blends	Helium-rich blends	No
Titanium	Thin and thick	100% argon	100% argon	Yes, always, plus trailing shield
Nickel alloys	All	100% argon	Argon, or Ar/H₂ on clean austenitic grades	Yes on roots where oxidation matters

These recommendations mirror the Linde GTAW selection matrix: mild steel manual, stainless manual, copper manual, and nickel manual all take argon; 300-series stainless with a slight oxide film moves to argon/hydrogen H-2 or H-5; aluminum manual runs argon or 75Ar/25He; copper mechanized goes argon/helium. The thickness split on stainless is worth memorizing: published TIG selection charts call for argon below 1/16 in. and push toward 95Ar/5H₂ or argon/helium above that line, because the extra thermal conductivity of those blends buys heat input and travel speed exactly where pure argon starts running out of punch. One caution on hydrogen: keep it to the H-2 and H-5 grades and reserve it for fully austenitic 300-series grades, because hydrogen can embrittle ferritic, duplex, and martensitic stainless.

Why Aluminum Is Mostly an Argon Job

Aluminum is the metal most readers will practice on, and pure argon covers it from sheet to half-inch plate. On AC, argon does double duty: it shields the puddle and, during the electrode-positive half of the cycle, the ionized gas actually scours the aluminum oxide film off the surface, which is why TIG welds on aluminum look so much cleaner than processes that lack that cleaning action. If you are still chasing porosity and sooty black welds on aluminum, the fix is often preparation rather than gas. A dedicated aluminum cleaner for welding plus a stainless brush used only on aluminum removes the hydroxide and oil that argon cannot fix. For thick aluminum plate and hull work, where you are pushing a wide, hot fillet, a 75Ar/25He blend is the standard upgrade. The hotter arc wets the puddle out instead of stacking it, which is exactly what aluminum boat welding joints demand.

Copper, Steel, and the Thickness Rules

Copper is the second metal where helium earns its invoice. Copper pulls heat out of the arc faster than almost anything else in the shop, so thick copper and copper alloy joints are the classic case for argon/helium, with pure helium reserved for heavy mechanized runs. Mild steel and low-alloy steel work rarely need anything beyond argon, manual or mechanized. The extra heat of a helium blend buys you little on steel and costs arc control. Titanium and nickel alloys, including specialty grades like Alloy 20, stay on pure argon for the arc itself and add a purge or trailing shield for coverage behind the weld. The gas inside the cup is only half the story on reactive metal.

Flow Rates, Cup Sizing, Gas Lens, and Draft

Choosing the gas is half the job; delivering it correctly is the other half. As a rule of thumb, manual TIG with a standard cup runs roughly 15–20 CFH of argon. A gas lens body lets you drop to 12–15 CFH while getting better coverage, because the lens breaks the flow into laminar layers instead of a turbulent jet. Larger cups on longer backsteps want more flow, not less. Helium-rich shielding gases require higher flow rates than argon to hold the same shield, so scale up when you switch blends. And critically, flow should be measured at the cup with a flow meter, not read off the ball in a rotameter hanging three feet from your hand.

Draft is the silent killer of TIG shields. If a fan or open door cannot be eliminated, Linde’s aluminum welding guidance offers a practical hierarchy: reduce the cup-to-work distance, increase flow, or move to a gas lens, which holds a stable laminar shield at distances and flow rates where a standard cup goes turbulent. Post-flow matters too. Leave the gas running one to three seconds after the arc stops so the hot puddle and the tungsten do not take their last breath in open air.

Finally, match the cylinder to the schedule. A single argon bottle covers the overwhelming majority of manual TIG work; blends are specialty purchases that make sense once you are welding production volumes of thick aluminum or stainless. Whether you buy locally or through a national distributor such as Airgas welding supplies, ask for welding-grade purity, not industrial grade, and confirm the gas designation on the label matches what your selection chart called for.

Common TIG Gas Mistakes and How to Troubleshoot Them

After dialing in your amperage and perfecting your torch angle, few things frustrate a TIG welder like watching a good weld fall apart because of shielding gas. The right bottle is only half the battle; how you flow, route, and protect that gas decides whether the puddle stays clean. Most TIG gas failures trace back to a handful of repeatable mistakes. Here is how to read the signature and fix it before you burn through more filler rod.

Porosity: Too Much, Too Little, or a Leak

Porosity is the most common gas-related defect in TIG welding. When atmospheric air contaminates the puddle, tiny pockets form through the bead and weaken the joint. Four causes cover nearly every case:

• Excessive flow: More gas does not mean better coverage. As Linde’s TIG welding gases guide explains, high flow turns turbulent and pulls in the very air it should exclude, especially in drafty shops.
• Insufficient flow: Too little flow lets oxygen and nitrogen reach the arc, causing a contaminated puddle and heavy oxidation on reactive metals.
• Leaks and damaged fittings: A loose hose, cracked O-ring, or worn quick connect bleeds off gas before it reaches the cup. Leak-test every connection with detection solution before striking an arc.
• Contaminants: Wet hoses, dirty regulators, or old cylinders introduce moisture into the stream. Surface prep matters as much as gas flow: a dedicated product like Aluminum Cleaner for Welding sharply reduces porosity before gas ever enters the picture.

Gray, Sooty Aluminum Welds

An aluminum bead that comes out dull, gray, and sooty is almost always a shielding problem. Drafts, an excessive cup-to-work distance, a cracked cup, or spatter blocking the gas path all let air reach the AC arc. Keep the cup close, keep consumables clean, and shield the work area from airflow, including fans and open doors.

Heat Tint Colors on Stainless Steel

A light straw tint on austenitic stainless is normal. Heavy blues, purples, and black are oxidation, not decoration. Insufficient coverage, missing post-flow, and a poor purge on tubing or enclosed parts are the usual gas-related culprits. On critical fabrications those oxides eat into corrosion resistance, so coverage and purge need planning whether you are in a shop or out in the field.

Wandering or Hard-to-Start Arcs

Gas selection changes arc physics, and the shift is most obvious when you move to helium blends:

• Helium blends: Pure helium and high-helium mixes require more energy to ionize than argon, so they are much harder to start without high frequency (HF) assistance.
• Worn consumables: A chipped cup, contaminated collet body, or loose gas lens creates turbulence that shows up as a wandering arc.
• Polarity errors: Wrong polarity for the process amplifies starting trouble, so verify your machine settings before blaming the bottle.

The numbers back this up. Published current and voltage windows place argon at roughly 80 to 150 A and 11 to 13 V, while an argon/helium A-50 blend runs 15 to 17 V on the same electrode and material. Same settings, different gas, different arc.

Regulators, Flow Meters, and Gas Densities

The most safety-critical mistake is misreading the gas itself. Density changes how shielding behaves and where it goes when it escapes the arc zone:

• Argon’s weight: With a relative density of 1.38, argon is heavier than air. HSE’s asphyxiation hazards guidance notes that it pools in pits, tanks, and vessel bottoms, creating an asphyxiation risk.
• Helium’s buoyancy: At a relative density of 0.14, helium rises and collects overhead. As The Fabricator points out, helium blends need higher flow rates to offset that upward dissipation.
• Equipment misuse: The wrong flow meter for your gas, a misread ball-type meter, or flow beyond the recommended range will all compromise the shield. For equipment standards, see AWS C5.10 and AWS A5.32, both of which point to ANSI Z49.1 for safe practice.

Quick Troubleshooting Reference

Symptom	Likely Gas-Related Cause	Fix
Porosity throughout bead	Flow too high (turbulence), too low, or fittings leaking	Set CFH to the recommended range for your cup, leak-test connections, block drafts
Gray or sooty aluminum	Air entrainment, contaminated gas, or cup spatter	Shorten cup-to-work distance, inspect consumables, verify gas purity, shield from wind
Heavy heat tint on stainless	Insufficient coverage or lack of purge/post-flow	Increase post-flow, use a gas lens, purge enclosed parts completely
Hard-to-start or wandering arc	Helium without HF start, worn cup, or wrong settings	Use HF start for helium blends, replace consumables, verify polarity and amperage
Erratic flow reading	Wrong flowmeter for the gas or damaged regulator	Check meter calibration for your specific gas, inspect hoses, follow manufacturer specs

Catching these mistakes early saves time, filler metal, and a lot of frustration. The extra minute you spend checking your gas system is one of the cheapest investments you can make in cleaner, stronger, safer welds.

Safety, Handling and Cost of TIG Shielding Gases

Shielding gases are inert, odorless and invisible, which is exactly what makes them risky: you cannot see an argon leak, smell a helium release, or notice oxygen being pushed out of the air you breathe. This section covers the health hazards, the handling rules and the honest money side of TIG gas, so you can buy, store and use cylinders with confidence.

The Silent Risk: Oxygen Displacement

Argon is heavier than air, so it sinks and pools in low areas: pits, trenches, tank interiors, floor sumps. Helium is lighter and climbs, collecting under tarps and in ceiling pockets. Carbon dioxide, though never a TIG shield, is heavier than air and pools even faster. In every case the result is the same, oxygen concentration in that space drops, and OSHA’s welding safety fact sheet warns that gases such as helium, argon and carbon dioxide displace oxygen in the air and can lead to suffocation, particularly when welding in confined or enclosed spaces.

What makes this lethal is how quietly it happens. The UK Health and Safety Executive notes that in an oxygen-deficient atmosphere you may not cough or feel breathless — you simply pass out. Multiple casualties often occur because rescuers rush in without testing the atmosphere first, and they collapse beside the original victim.

Practical rules that follow from this:

• Test before entry, every time, using a calibrated oxygen meter — not a “wave your hand and sniff” check.
• Ventilate the area and purge lines before striking an arc inside any enclosure.
• Post an attendant outside confined spaces and agree on a rescue plan that involves testing first, not entering first.
• Check regulator and hose fittings for leaks with leak-detection solution, especially after cylinder exchanges.

Cylinder Handling: What OSHA Requires

Under 29 CFR 1926.350, compressed gas cylinders must have valve protection caps in place whenever they are not connected for use, must be secured upright at all times so they cannot fall, and must be kept away from sparks, slag and other sources of heat. The same rule states plainly that no person other than the gas supplier may attempt to mix gases in a cylinder. You do not top off a bottle, blend your own argon/helium mix in the shop, or refit a valve yourself: the supplier handles mixtures under controlled conditions with proper equipment. Secure, cap, keep cool, and leave mixing to the professionals.

Storage basics: keep cylinders upright and chained or strapped, cap them during transport with a purpose-built cart, never drag or drop them, and store them away from electrical circuits, hot work and acid. If you are setting up a shop’s gas supply, a supplier such as AllGas Welding Supply can walk you through cylinder sizes, regulator pairing and exchange logistics.

Purity: Why Welding-Grade Argon Is Not “Just Argon”

Welding gas is specified far more tightly than industrial argon. AWS SG-A requires a minimum purity of 99.997% with a dew point no higher than −76°F (−60°C) — see AWS C5.10/C5.10M for shielding gas classification. That dew point matters: moisture in the bottle ends up in the arc and shows up as porosity. Buy from a supplier with good turnover, keep hose fittings clean and capped when disconnected, and change cylinders before you run a bottle completely dry and start drawing the last dregs of possible contamination.

What It Actually Costs

Argon is the cheapest option by a wide margin, which is one more reason it is the default. Linde and other suppliers price pure argon well below blended gases, and the HSE points out that mixed gases such as argon/helium are significantly more expensive than pure argon — which is why large-scale purging jobs use pure argon rather than a blend.

Gas	Relative cost	Where it earns its price
100% argon	Lowest	Manual TIG on nearly every metal; purging; trailing shields
Argon/helium blends	Moderately higher	Thick, conductive metals and mechanized work where speed pays
Argon/hydrogen blends	Premium	Stainless production welding where bead color and travel speed matter
Premixed bottles vs. bulk	Exchange fee + rental	Small shops; bulk or tube supply for high-volume users

Work out cost per welded inch, not cost per cubic foot. A hotter blend that lets you run 30% faster on heavy aluminum may be cheaper overall than bargain argon — but for a hobbyist running a few hours a week, plain argon almost always wins. Cylinder rental, deposit and exchange fees vary by supplier, so ask what is included when you compare quotes.

Bottom line: buy the right gas, secure the bottle, test the atmosphere, and treat every cylinder as a pressurized safety device rather than a shelf item. That discipline costs nothing and protects everything.

Conclusion: Choose Your TIG Gas with Confidence

Shielding gas is the one variable in your TIG setup that costs the least to fix and hurts your welds the most when it is wrong. A worn cup or a mediocre torch can be worked around; a contaminated or mismatched bottle simply will not give you a clean arc. The good news is that the whole decision collapses into a few plain rules you can hold in your head at the supply counter.

Praxair’s blend datasheet puts argon first for a reason: it starts easily, gives maximum cleaning action on AC aluminum, and puts you in control of bead shape and distortion. Everything else in this guide is a variation on that baseline, adopted only when a specific job earns it.

The Framework, In Order

1. Start with 100% argon for every manual TIG job. Steel, stainless, aluminum, magnesium, copper, titanium, nickel: one bottle covers them all. It is the default for a reason, and it is what almost every shop keeps on the rack.
2. Add helium only when the metal or the cycle time demands it. Helium raises arc voltage and heat input, so penetration grows in a predictable way — the more helium in the mix, the deeper the penetration and the higher the flow you will need. Reserve argon–helium blends for thick stock, highly conductive copper and aluminum, and mechanized work where travel speed pays the bills.
3. Consider argon–hydrogen only on austenitic stainless and certain nickel alloys. Small hydrogen additions produce a reducing atmosphere that improves wetting, bead color and speed. On carbon steel, aluminum, copper, galvanized or coated steels, hydrogen is forbidden — it buys you porosity and cracking instead of shine.
4. Never run CO2, oxygen or nitrogen as a GTAW shield. CO2-containing MIG mixes attack the tungsten and destabilize the arc, oxygen is used only as a tiny controlled addition in mechanized processes, and nitrogen is not an inert shield for GTAW. Check the cylinder label against the classification before you light up.
5. Match flow to the cup, the gas lens and the room. A gas lens lets you run a lower, wider, calmer flow than a standard collet body. Bigger cups want more gas, open shops want more gas, and anything past the useful range just creates turbulence that sucks air into the shield.
6. Treat the cylinder as safety equipment. Secured upright, valve cap on, regulator undamaged, no improvised mixing, and aware that argon and CO2 pool low while helium rises — colorless, odorless, and unforgiving in confined spaces.

One last habit worth building: gas selection is not a decision you make once. Linde’s selection guidance is explicit that the first-choice blend often needs refinement as the work progresses, because the equipment you own and the skill you have on hand matter as much as the textbook recommendation. Dial the flow in, watch the puddle, and adjust. As Nippon Sanso notes, the gas you pick influences travel speed, porosity, penetration, bead appearance, distortion, post-weld cleanup and even operator comfort — so a ten-minute test weld on scrap is cheap insurance.

If you are still building your setup, the fundamentals matter as much as the bottle: correct aluminum preparation before welding removes the oxide and oils that no amount of gas will compensate for, and training in aerospace TIG standards is the fastest way to see how tightly gas control is specified in high-stakes work. When it comes time to order, a supplier that walks you through cylinder sizing, exchange programs and gas handling will save you money and surprises.

Pick argon, protect the arc, verify the label, and let the weld tell you when something changed. That is the entire discipline of TIG shielding gas — and once it is habit, you will spend your time on technique instead of chasing pores.

Frequently Asked Questions

Can I use 75/25 argon/CO2 MIG gas for TIG welding?

You should not. CO2 dissociates at arc temperatures and oxidizes both the tungsten electrode and the weld puddle, causing an erratic arc, rapid electrode degradation and poor weld quality. TIG shielding should be pure argon, helium, or an argon-based inert blend — CO2 mixes belong to MIG (GMAW) and flux-cored work.

What is the best TIG welding gas for aluminum?

For manual AC TIG welding, 100% argon is the best all-around choice because it arc-starts easily, gives strong cleaning action and the best puddle control with the lowest gas consumption. For thick aluminum or mechanized work, argon/helium blends such as 75Ar/25He add penetration and travel speed.

Do I need a special gas for TIG welding stainless steel?

Pure argon works well for manual TIG on stainless. For better bead color, wetting and travel speed on 300-series austenitic stainless, an argon/hydrogen blend (typically 2–5% hydrogen) is the professional choice — but never use hydrogen blends on carbon steel, aluminum, copper or galvanized material, where they can cause porosity and cracking.

What flow rate should I use for TIG shielding gas?

Most TIG charts call for roughly 5–20 CFH (about 2.5–10 L/min) with a standard cup, scaling up with electrode and cup size — for example 10–15 CFH on 3/32 in. tungsten. Measure flow at the torch with a flow meter, and remember that too much flow is as bad as too little because turbulence pulls air into the shield.

Is helium worth the extra cost for TIG welding?

Usually only for specific jobs: thick aluminum or copper sections, high-speed mechanized welding, or situations where deeper penetration lets you skip a bevel. For everyday manual work on thin material, pure argon gives better arc control at a fraction of the price, and helium-rich blends cost significantly more per cylinder.

Can I use nitrogen or pure oxygen as a TIG shielding gas?

No. Oxygen is never used as a shielding gas at 100% because it oxidizes the tungsten and the puddle, and nitrogen is not a true inert gas at welding temperatures — it reacts with metal and offers none of argon’s arc stability. Both can appear in specialized blends, but never as the primary GTAW shield.

Why are my stainless TIG welds blue, purple or straw colored?

Those colors are heat tints — thin oxide films that form when hot stainless meets oxygen. They usually point to insufficient gas coverage, no back purge on the root side, excessive heat input or travel that is too slow. Light straw is generally cosmetic; gray or black scale means serious contamination that should be wire-brushed or chemically cleaned.

Why are my aluminum TIG welds gray, sooty or porous?

That is almost always a shielding problem: wrong gas (such as a CO2 mix), flow that is too high or too low, a draft, a leaking fitting, or inadequate pre-weld cleaning. Confirm the cylinder is pure argon, check fittings with leak detection fluid, shield the arc from airflow, and clean the base metal with a dedicated stainless brush.

Can I mix shielding gases in my own cylinder?

No. OSHA’s construction welding standard prohibits anyone other than the gas supplier from mixing gases in a cylinder, and cylinders must meet DOT specifications. Buy premixed blends from your supplier with the exact percentages written on the certificate and the cylinder label.

What are the main safety risks of TIG shielding gases?

The biggest one is asphyxiation: argon and carbon dioxide are heavier than air and can pool in pits, tanks and vessel bottoms, while helium rises into high spaces — and none of them have an odor. Ventilate and test oxygen levels before entering any confined space, and always secure cylinders upright with valve caps in place.