Platinum (Pt) is a noble metal, prized for its natural resistance to chemical degradation and exceptionally high density. This rarity and stability make it valuable across diverse fields, from fine jewelry to advanced industrial applications. As one of the densest metals, platinum is noticeably heavier than gold or silver of the same size, a physical trait that contributes to its perceived value and durability. Unlike gold, which is frequently alloyed to increase its hardness, platinum is often utilized in commerce at very high purity levels. The precise purity of a platinum object is a primary factor determining its function, market value, and specific use.
Quantifying Platinum Purity
The purity of platinum is measured using the millesimal fineness system, which expresses the amount of pure metal in parts per thousand by weight. This system allows for precise labeling of the platinum content within an alloy, regardless of the other metals present. For example, a piece of metal stamped with “950” means that 950 out of 1,000 parts, or 95.0%, of its total weight is pure platinum.
This measurement system is often informally described using the “nines” notation for extremely high purities. A fineness of 999, which is 99.9% pure, is referred to as “three nines fine.” This system highlights the minute difference in impurity levels at the highest commercial grades.
Achieving absolute 100% purity is practically impossible in commercial refining and manufacturing processes. Therefore, the term “chemically pure” typically refers to the highest achievable and measurable grade, often 99.9% or 99.95%. The purity level is always measured by weight because the mass of the precious metal dictates its intrinsic value.
Platinum Purity Standards in Jewelry
The standards for platinum jewelry are regulated to ensure consumers receive a consistent and verified product. The most common and widely accepted fineness is the 950 standard, meaning the metal is 95% pure platinum. The remaining 5% is an alloy of other Platinum Group Metals (PGMs) or base metals intended to enhance the material’s properties.
Alloying is necessary because pure platinum, while dense, is relatively soft and could wear down more easily in daily use. Metals like Ruthenium or Iridium are frequently added to 950 platinum to increase its hardness and improve its scratch resistance. The addition of these specific metals ensures the resulting alloy maintains platinum’s natural, bright white color and hypoallergenic qualities.
A slightly lower standard, 900 fineness, or 90% pure platinum, is also used in jewelry, offering increased durability for certain designs or settings. To legally verify these purity levels, items are marked with a small stamp, or hallmark, such as “950 Pt” or “Pt900.” This hallmarking serves as a legal guarantee of the metal content.
Investment-Grade and Industrial Purity Levels
Purity requirements outside of consumer jewelry tend to be much stricter, especially for financial and technological applications. Investment-grade bullion, such as platinum bars and coins, is typically required to meet a minimum fineness of 999.5, or 99.95% pure platinum. This “three nines five” standard represents the highest purity level commonly traded on global commodity markets.
This extreme purity is necessary for industrial uses where even trace impurities can compromise performance. Platinum’s most significant industrial role is as a catalyst in automotive converters, which use the metal’s unique surface chemistry to convert harmful exhaust emissions into less damaging substances. In this application, impurities can “poison” the catalyst, inhibiting its function and reducing its lifespan.
In medical and scientific fields, ultra-high purity platinum is non-negotiable due to the need for biocompatibility and inertness. Platinum is used in medical implants like pacemakers, stents, and specialized thermocouples because it does not react with body tissue and can withstand high temperatures without degradation. The consistent atomic structure of 99.95% platinum ensures reliability in these precise, life-dependent devices.