The question of whether platinum is stronger than gold is common, particularly for those investing in fine jewelry. Comparing these two precious metals requires adopting the precise language of metallurgy, as “strength” is not a single property. A material’s perceived strength is a combination of characteristics that determine how it behaves when subjected to various forces. To accurately assess which metal is technically superior, one must look at how each metal resists scratching, breaking, and permanent deformation.
Defining Metal Strength: Hardness and Tensile Strength
In the study of materials, a metal’s capacity to withstand external forces is broken down into distinct mechanical properties. One of these properties is hardness, which describes a material’s resistance to surface deformation, indentation, or scratching. Hardness is commonly measured using scales like the Vickers Hardness (HV) test, which uses a diamond indenter to determine how easily a material can be permanently marked.
Another important property is tensile strength, which measures a metal’s resistance to being pulled apart before it fractures. A material with high tensile strength can bear a significant pulling force without breaking, making it structurally robust. These two factors are separate from a metal’s ability to be shaped, which is defined by malleability and ductility.
Malleability is the capacity for a metal to be hammered or compressed into thin sheets without cracking. Ductility is the ability to be stretched or drawn into a wire without fracturing. Both gold and platinum are highly malleable and ductile, but their varying degrees of these properties contribute to their behavior in finished products.
Platinum vs. Gold: Comparing Inherent Hardness
When comparing the pure forms of these metals, a direct answer to the strength question is complicated. Pure gold (24 karat) is extremely soft and easily scratched, with a Vickers hardness value around 25 HV. Pure platinum, while significantly denser than gold, is also relatively soft in its pure form, registering a Vickers hardness of about 56 HV.
However, jewelry is almost never made from pure metal, and the most common jewelry alloys change this comparison dramatically. Standard gold jewelry is typically 14K or 18K, meaning it is alloyed with metals like copper, silver, or nickel to increase its durability. An 18K gold alloy can have a hardness ranging from 125 to 180 HV, and a 14K gold alloy can be even harder, sometimes reaching 200 HV.
Standard jewelry platinum is often 90% or 95% pure, alloyed with metals like iridium or ruthenium. While these alloys increase platinum’s hardness, the resulting material is generally softer than common 14K gold alloys, often remaining below 120 HV. Consequently, the gold alloys used in jewelry are often more resistant to surface scratching and indentation than platinum alloys.
Despite the lower scratch resistance, platinum often possesses a higher ultimate tensile strength than gold alloys, meaning it is more difficult to snap or break under tension. For instance, while some 18K gold alloys can reach tensile strengths of 300 MPa, platinum alloys are renowned for their superior structural integrity and resistance to fracture. This characteristic is particularly important for small, stressed components like the prongs that secure a gemstone.
Practical Durability and the Role of Alloys
The simple hardness comparison is often misleading when considering a piece’s long-term durability during daily wear. Alloying metals are paramount, as they are specifically chosen to enhance certain properties. Gold alloys are made harder to resist scratching, but when gold is scratched, a small amount of the metal is physically lost from the surface. Over years of wear, this material loss can be substantial, causing prongs to thin and details to wear down.
Platinum, on the other hand, is a dense and highly malleable metal, which alters how it reacts to contact. When a platinum surface encounters another object, the metal is not scraped away but rather displaced, meaning it is pushed aside and forms a small ridge. This displacement effect is what causes a platinum piece to develop a soft, satiny finish over time, often called a patina.
Crucially, the metal remains on the piece, preserving the original weight and volume, even after developing the patina. A jeweler can restore the original high polish simply by burnishing the surface to move the metal back into place, resulting in virtually no material loss. This means that while a 14K gold ring may be more scratch-resistant, a platinum ring will maintain its structural integrity and material volume better over a lifetime of wear.