Bronze is made of two metals: copper and tin. That pairing, not a single element, defines what bronze is and explains why it behaves the way it does. Copper gives the alloy its base structure and workability; tin adds hardness and resistance to corrosion. Most bronze you encounter is roughly 88% copper and 12% tin, though modern foundries adjust the ratio for specific jobs. If someone asks what bronze is made of, the accurate answer is copper plus tin, with a clear distinction from brass, which is copper plus zinc.
Bronze: A Copper-Tin Alloy
Bronze is made of two metals in the strictest sense: copper and tin. The alloy has been produced for thousands of years, and the modern definition still centers on that copper-tin combination. This matters because people often treat 'bronze' as a vague name for any brown-ish metal, but the composition is not vague at all. A material labeled bronze normally contains copper as the majority element and tin as the deliberate addition that changes its mechanical character. The source that compares brass and bronze for manufacturing puts it plainly: bronze is primarily a copper-tin alloy, and that is what separates it from brass, which is copper-zinc. That source does more than name the ingredients; it links the copper-tin base to specific application advantages, such as seawater resistance and heavy-load service. So when you read a datasheet that says 'bronze,' you should expect copper and tin in the list of components. The exact percentages vary—some phosphor bronzes, aluminum bronzes, and silicon bronzes swap part of the tin for other elements—but the two-metal core of the definition remains. That core is not an academic detail; it drives the hardness, corrosion resistance, and load capacity that engineers rely on. Understanding this distinction is the first step toward picking the right red metal for a bearing housing or a marine fitting.
Why does the question 'bronze is made of what two metals' come up so often? Because bronze, brass, and copper look similar at a glance, and suppliers sometimes label products in ways that blur the lines. A design engineer staring at a stack of metal bars may not be able to tell the difference by eye. The elemental composition is what separates them, and that composition is invisible without a datasheet. For a buyer, the label is only the beginning; the real information lives in the alloy specification. The machining guide for these metals notes that brass, bronze, and copper have overlapping characteristics but distinct elemental makeups, and those differences matter once the cutter meets the material. Bronze is defined by copper plus tin; brass is defined by copper plus zinc; copper is a single element. The practical consequence is that you cannot substitute one for another simply because they share a reddish hue. A part that works as a brass fitting can fail as a bronze bushing, or vice versa, if the corrosion behavior or hardness is wrong. That is why the two-metal answer is not trivia: it tells you which performance profile you are actually getting. Once you know bronze is copper-tin, you can ask the next question—what does each metal contribute—and that is exactly where material selection gets technical. That is where the rest of this guide picks up.
Copper's Role and Tin's Role
What does each metal actually do inside bronze? Copper is the base that gives the alloy its formability and electrical conductivity; it is the reason bronze can be cast, extruded, and machined at all. Tin is the harder, more corrosion-resistant partner that stiffens the mix. When you increase tin, hardness goes up, but the alloy becomes more brittle and harder to machine. The CNC machining comparison between brass and bronze shows this trade-off clearly: brass, with zinc instead of tin, cuts easily, produces fine finishes, and keeps tool wear low, which makes it ideal for high-volume precision components. Bronze, with tin, is more demanding on the machine but earns its place in bearings, bushings, and load-bearing parts where wear resistance and durability matter more than cycle time. The same source points out that bronze often gets chosen for corrosion-prone environments because tin protects the surface better than zinc does. This is why datasheets list the exact tin percentage; a small change from 10% to 14% tin shifts the alloy from a bearing material to a gear material. That same mechanism is what separates bronze from brass in real service. So the answer to 'what do the two metals do' is simple in principle: copper builds the body, tin builds the resistance. The ratio controls the balance between machinability and endurance.
A useful working definition for bronze is an alloy of copper and tin in which copper dominates. The most commonly cited ratio is 88% copper and 12% tin, a combination that balances strength, castability, and corrosion resistance. This exact split appears in engineering guides that compare brass and bronze, and it is a good baseline even though foundries adjust it for specific applications. A higher tin content produces harder, more wear-resistant alloys for heavy gears, while a lower tin content improves machinability. The economic side reinforces the same point: because tin is expensive—copper prices around $13.34 per kilogram and tin around $53.46 per kilogram as of early 2026—bronze typically costs 40–60% more than brass, which uses inexpensive zinc instead. That price gap is not wasted money when the application needs bronze's durability, but it explains why manufacturers shop carefully. The 88/12 ratio is a definition in the same way a recipe is a definition: it tells you the ingredients and the proportions, and deviations are named by their added elements, such as phosphor bronze or aluminum bronze. For a bearing buyer, that 88/12 baseline is more useful than a vague color check, because it predicts how the alloy will behave under load.
Bronze vs. Brass: Not the Same Blend
Is brass just another name for bronze? No, and the difference is not cosmetic. Brass is a copper-zinc alloy, while bronze is a copper-tin alloy. That one-letter change in the second metal produces different mechanical properties and different failure modes. The manufacturing comparison between the two highlights what this means in practice: brass offers excellent machinability, good electrical conductivity, and a bright gold finish, which makes it a favorite for valves, fittings, and decorative components. Bronze, with tin as the partner, delivers superior wear and corrosion resistance, greater hardness, and higher strength, which is why it shows up in bearings, marine fittings, and parts that face harsh environments. Zinc, unlike tin, is vulnerable to dezincification, a form of corrosion that leaches zinc out of the alloy and leaves a weak, porous copper structure. Tin does not suffer that failure in the same way, so bronze holds up better in saltwater and industrial fluids. If you swap brass for bronze in a seawater application, you are not just changing the color; you are changing the alloy's ability to survive. That is why the two-metal answer matters for anyone selecting materials. And that survival advantage is exactly what the composition tells you before you ever run a test.
The practical difference shows up in the standard alloy families. A typical listing of Fraser alloys gives bronze grades like C83600 and C84400, both leaded gunmetals, with excellent machinability and good pressure tightness. C86300 and C86500 are manganese bronzes with exceptional strength but only fair machinability. C90700, a phosphor bronze, combines good machinability with high strength and good corrosion resistance, suitable for heavy-duty gears and bearings under medium to high loads. These are not abstract labels. The standard designations tie each alloy to a documented specification, so a buyer can verify composition and properties before ordering. The reason these grades exist separately is that the copper-tin base can be modified with small amounts of lead, phosphorus, manganese, or zinc to tune performance. That means 'bronze' is a family, not a single formula; still, every member of the family is built on copper and tin. When you see a bearing designated C90700, you know tin is doing the heavy lifting against wear and corrosion, and you know the part was selected because brass would fail under that load. This is exactly the kind of decision that the simple copper-tin composition unlocks. The path from composition to specification is direct, and that directness is what makes the copper-tin composition useful on the shop floor.
Choosing Bronze for the Right Job
How do you decide when bronze is the right choice? Start with the environment and the load. If the part will rub against another surface, carry a heavy bearing load, or sit in saltwater, bronze is the safer bet. The machining and application guide for copper, brass, and bronze puts it bluntly: selecting the wrong red metal can cause catastrophic component failure, from overheated electrical connectors to seized marine fittings. Brass has its strengths—high-speed machining, lower cost, bright finish—but it is not built for anti-friction or corrosion-dominated jobs. Bronze is, and that is why it appears in bearings, bushings, gears, valve seats, and pump components. The guide identifies bronze C93200 as the go-to for anti-friction and wear resistance, a practical shorthand for engineers who need a material that survives sliding contact. The decision rule is not 'bronze is better'; it is 'bronze is better when the job demands wear resistance, corrosion resistance, or load capacity.' If the job is high-volume precision machining with thin walls or fine cosmetic finishes, brass will beat bronze on cost and cycle time. You choose by matching the alloy to the stress, not by picking the more prestigious name. That is the selection logic in one sentence.
Here is the verdict you can use: bronze is made of copper and tin, and that combination is the reason it earns a place in bearings, shafts, and gears. When you need a material that can carry a load, shrug off corrosion, and resist wear, bronze is the alloy with the right resume. The practical side of this is that you can actually buy the material without guessing. Online Metals lists bronze as a standard category alongside brass and carbon steel, with machine-ready stock and products aimed at bearings, shafts, and gears. Their site shows bronze among the alloy families, and their product categories include Bearings, Shafts and Gears, which is exactly where bronze earns its keep. Contact information like 888-527-3331 appears on the site, but the more important takeaway is that a supplier explicitly separates bronze from brass, reinforcing that the material distinction is real and practical. So when you ask 'bronze is made of what two metals,' the answer is copper and tin; when you ask when to use it, the answer is whenever the application punishes softer or less corrosion-resistant alloys. That is the judgment rule that turns a chemistry fact into an engineering decision.
So the material comes down to two metals: copper and tin. Copper provides the structure; tin provides the hardness and corrosion resistance. That combination is why bronze belongs in bearings, marine parts, and other load-bearing components, and it is also why bronze should be chosen over brass whenever wear and corrosion dominate. Once you need machinability and low cost instead, brass takes over. That two-metal composition is not a trivia fact; it is the foundation of every material decision that follows.
