Bronze is made of two metals: copper and tin. Tin is the element that gives bronze its hardness, wear resistance, and corrosion resistance—especially in saltwater. That same tin separates bronze from brass, which uses zinc instead. Bronze is not a single fixed recipe but a family of copper-tin alloys, with tin content ranging from a few percent to over 20 percent depending on grade. This guide explains the composition, how bronze differs from brass, common bronze alloys like C83600 and C90700, and when to pay the premium for bronze.
Bronze Is Copper + Tin
Bronze is made of two metals: copper and tin. That is the direct answer, and it is also the answer that separates bronze from brass, its lookalike cousin, which uses zinc instead. In standard casting bronze, the mix is roughly 88% copper and 12% tin, a ratio that shows up consistently in engineering references such as a January 2026 selection guide. The copper supplies the base conductivity, ductility, and workability that any alloy needs, while the tin is the element that changes the alloy's personality. Tin increases hardness, improves the casting flow, and gives bronze its signature resistance to corrosion and wear in saltwater and high-friction environments. This is not a minor footnote. It is the reason bronze appears in marine hardware, bushings, bearings, and heavy-duty gears, where brass would fail or wear out quickly. The evidence is right in the numbers: copper alone is soft and reactive, but adding tin transforms it into a bearing metal. So when someone asks what bronze is made of, the answer is copper and tin, and that pairing is the foundation for everything else in this guide. Bronze is not a single fixed recipe, of course; it is a family of copper-tin alloys with tin content ranging from a few percent to over 20 percent depending on grade. But the defining pair remains copper and tin, and it is the tin that makes bronze bronze.
That straightforward answer naturally raises a follow-up: what about brass? Bronze and brass look similar, often share a warm gold or reddish tone, and both are copper alloys. But the second element is different. Brass is made from copper and zinc, not copper and tin. That one-word difference in composition leads to very different behavior in the workshop and in service. If you have ever held a brass fitting next to a bronze bushing, you know they feel different: brass is typically brighter and harder to the cutter, while bronze has a deeper color and a denser feel. The practical question is whether you need tin's corrosion resistance or zinc's easy machining, and that trade-off runs through every material selection. Understanding the difference is not an academic exercise. When you order metal online, the alloy name tells you exactly what you are getting, and the choice between bronze and brass can mean the difference between a part that lasts years and one that fails in months. Many people assume the two are interchangeable, or that bronze is simply 'copper with something' and brass is 'copper with something else.' In fact, they are distinct families with distinct personalities. Brass's zinc content makes it cheaper and easier to machine, which is why it dominates plumbing fixtures and decorative hardware. Bronze's tin content buys you wear resistance and corrosion resistance, which is why it shows up in bearings and marine parts. That is the fork in the road, and once you see it, you cannot unsee it.
Why does tin matter so much? The mechanism is straightforward. Copper by itself is relatively soft and ductile; it deforms under load and oxidizes in saltwater. Adding tin interrupts the copper crystal lattice and creates harder, more wear-resistant phases. That is why tin bronze grades like C90700 phosphor bronze are specified for heavy-duty gears and bearings with medium to high loads. The alloy grade data shows C90700 with good machinability, high strength, and good corrosion resistance. Tin also shifts the electrochemical behavior of the alloy, reducing the rate of corrosion in marine environments. A manufacturing guide from HMaking makes the point bluntly: selecting the wrong red metal can cause catastrophic component failure, such as marine fittings seizing due to saltwater corrosion. In contrast, a zinc-based alloy like brass is vulnerable to dezincification in saltwater, which is why high-zinc alloys account for a large share of marine hardware failures. So the tin is not a filler; it is the active ingredient that gives bronze its industrial identity. Even a few percent of tin changes the alloy's behavior dramatically, which is why bronze can handle the sliding contact and salt spray that would destroy brass.
Bronze vs. Brass: The Second Element Matters
The cleanest way to see the difference is to put the two definitions side by side. Bronze is a copper-tin alloy; brass is a copper-zinc alloy. That is the elemental fact that drives everything else. The Zintilon machining guide notes that it is difficult to detect the subtle differences with the naked eye, which is why engineers often confuse them. But the composition is not subtle. Brass typically contains 60-70% copper with the balance zinc, while bronze uses tin in place of zinc. The practical consequence is that brass has higher electrical conductivity and machines extremely well, while bronze has superior wear resistance and corrosion resistance. A CNC machining comparison published by JLCCNC puts it in terms of the cutter: brass gives you faster cycles, lower tool wear, and fine surface finishes; bronze gives you a tougher, more abrasive cutting experience but a part that lasts longer in service. So if you are choosing a material for a valve or a decorative fitting, brass is often the efficient choice. If you are choosing a bearing or a marine fitting, bronze is the reliable one. The second element is not just a recipe detail; it is the whole story.
The cause-and-effect chain runs from composition to behavior. Zinc in brass makes the alloy softer and more free-cutting, which is why brass is the default for high-volume precision parts with thin walls or fine cosmetic finishes. You can run brass at higher speeds with less tool wear, and that directly lowers cost per part. Tin in bronze makes the alloy tougher and more resistant to galling, so it earns its place in bearings, bushings, and load-bearing or corrosion-prone components. The uneed guide summarizes it well: brass shines in high-volume precision machining; bronze often wins where wear resistance and durability matter. There is a trade-off in machining too: bronze is harder on tools and slower to cut, but the part you end up with can handle higher loads and harsher environments. That is why a bronze bushing will outlast a brass one in a dusty or salty setting, even though both look similar at a glance. The alloying element dictates the failure mode: zinc-based brass can dezincify and weaken in saltwater, while tin-based bronze forms a stable protective layer. This is the practical meaning of the second element: it determines how the part fails.
In the workshop, you can often tell them apart without a label. Bronze tends to have a reddish-brown or darker brown color, while brass is brighter and more yellow-gold. Drop a small sample and listen: bronze has a duller, deeper ring, while brass sounds a bit more tinny. More usefully, think about where you see them. Brass appears in faucets, valves, door hardware, gears in light-duty mechanisms, and musical instruments. Bronze appears in ship propellers, underwater fittings, sleeve bearings, gears that take heavy loads, and bushings that see continuous sliding. If a part is going to sit in saltwater or carry a heavy rotating load, choose bronze. If it is going to be machined in high volume and does not face corrosion, brass is the economical pick. These are rules of thumb, not absolutes, but they save you from ordering the wrong metal from an online metals supplier. And when you do order, the designation tells you the truth: C8xxxx and C9xxxx numbers are bronze family grades, while C2xxxx numbers are brass grades. The color test is not perfect, but for most people it is enough to avoid a costly mix-up.
Common Bronze Alloys: Tin Is Only the Start
Bronze is not one alloy; it is an entire family of copper-tin alloys, and the grades are designed for different jobs. Casting bronze C83600, known as leaded gunmetal, offers excellent machinability, medium strength, and good pressure tightness, which makes it a workhorse for pump components and general castings. At the other end, C90700 phosphor bronze has high strength and good corrosion resistance, and it is specified for heavy-duty gears and bearings with medium to high loads. Between those two, the table from Fraser Alloys lists C84400 for pump industry bearings and C86300 manganese bronze with exceptional strength for heavy-duty applications. The point is that the tin content, and the small additions of lead or phosphorus, tune the alloy for a specific balance of machinability, strength, and corrosion resistance. So when you see a bronze grade on a supplier's page, the number encodes a promise about how the metal will behave. This is why bronze feels like a family of materials rather than a single metal: each grade is a deliberate recipe with a purpose. You are not buying 'bronze'; you are buying a specific grade with known limits.
Once you know the family, the applications make sense. The HMaking guide is blunt: selecting the wrong red metal can cause catastrophic component failure, and the examples are concrete. Electrical connectors overheat when someone uses a low-conductivity bronze where copper is needed. Marine fittings seize because a zinc-based brass was used instead of a tin-based bronze. The right application for bronze is where friction, load, and corrosion meet. Bronze bearings and bushings handle continuous sliding contact; phosphor bronze grades like C90700 are used in gears and heavy-duty bearings. Bronze propeller shafts and underwater fittings survive saltwater because tin resists the de-zincification that destroys brass. The brass-versus-bronze selection guide from Neha Motaiah emphasizes that bronze's superior wear and corrosion resistance makes it the go-to for bearings, marine fittings, and parts that face harsh environments. In short, bronze earns its place wherever brass would wear out or corrode. It is the alloy for the places where failure is not an option.
Why do tin-based alloys suit these harsh jobs? The reason is the microstructure. Tin atoms dissolve into the copper lattice and create harder, more wear-resistant phases. They also change how the alloy reacts with oxygen and saltwater, forming a stable, adherent oxide film that slows further corrosion. This is the same mechanism that makes bronze good for bearings: the surface can run against a steel shaft without galling, and if it does wear, it wears gradually rather than seizing. In contrast, zinc in brass is more electrochemically active, and in saltwater, it can leach out of the alloy, leaving behind a weak, porous copper structure. That process, called dezincification, is why brass fittings fail in marine environments. So the tin does double duty: it strengthens the bulk material and it stabilizes the surface. That is why a bronze bushing can run for decades in a wet, gritty environment, while a brass one might fail in months. The microstructure is the hidden contract between the metal and the application.
Buying Bronze: A Practical Verdict
Cost is where the composition really shows up. In January 2026, the London Metal Exchange had copper at roughly $13.34 per kilogram, tin at $53.46 per kilogram, and zinc at just $3.31 per kilogram. Since bronze uses costly tin and brass uses cheap zinc, the price gap is structural. The Baosheng guide puts the spread at 40-60%, meaning bronze is typically a half to two-thirds more expensive than brass for the same form. If you are buying a small bronze bushing, the difference might be a few dollars; if you are ordering a large batch of marine fittings, it can be thousands. That is the real decision context: tin is the costly ingredient, and you are paying for its corrosion resistance and wear performance. The trade-off is simple on paper: bronze costs more but lasts longer in harsh environments, while brass is cheaper and easier to machine. The question is whether your application needs tin's performance. For a decorative part indoors, brass is often the rational choice. For a bearing or a saltwater fitting, bronze is money well spent.
So how do you choose? Start with the environment. If the part will face saltwater, acid, or continuous friction, pick a tin-based bronze. If it is an indoor, low-load, high-volume part where machinability and cost dominate, brass is usually the better call. The JLCCNC guide frames it as a practical selection rule: tool wear, cycle time, surface finish, and scrap risk all favor brass, while service life, load capacity, and corrosion resistance favor bronze. Ask yourself three questions. Will the part be exposed to moisture or chemicals? Does it bear a load or slide against another surface? Is the cost of failure high? If you answer yes to any of those, bronze is worth the premium. If not, brass will save you money and machine faster. There is no universally better metal; there is only the metal that matches the job. And remember that each bronze grade has its own personality, so check the supplier's spec sheet, not just the name 'bronze.'
The verdict is straightforward. Bronze is made of copper and tin, and that tin content is the reason it exists as a separate material from brass. The uneed guide puts it in terms of matching material to performance: brass wins on machinability and cost for high-volume precision parts, while bronze wins on wear resistance and durability for bearings, bushings, and corrosion-prone components. When someone asks what bronze is made of, the answer is copper and tin, and the practical corollary is that you choose bronze when the job demands tin's performance. That might be a marine fitting that will live in saltwater, a bushing that carries a heavy load, or a gear that sees continuous abrasion. When the job is dry, light, and volume-sensitive, brass is the sensible alternative. So the two-metal answer is not just a trivia fact; it is the foundation of a material selection decision. Copper gives bronze its base character, tin gives it its edge, and together they define when bronze is worth the cost.
Buy bronze when the part will fight corrosion or friction; buy brass when it will not. That is the practical verdict behind the two-metal answer: copper + tin.
