Platinum is a rare, dense, and naturally white precious metal prized for its durability in fine jewelry and stability in industrial applications. Designated Pt on the periodic table, it is significantly more scarce than gold and highly valued for its resistance to corrosion. Identifying genuine platinum requires moving beyond a simple visual check, as many other white metals mimic its appearance.
Identifying Marks and Hallmarks
The simplest way to begin verifying a platinum piece is by locating an official purity stamp, or hallmark, typically found in inconspicuous places. On rings, this marking is usually stamped on the inner band, while on necklaces or bracelets, it is found on the clasp or a nearby tag. These stamps use a millesimal fineness system, indicating purity in parts per thousand.
The most common fineness mark is “950,” guaranteeing the item is 95% pure platinum. Other accepted markings include “900” or “850” for lower purities, or simply “PLAT” or “PT.” The presence of “Pt950” is a strong initial indicator of authenticity, though the absence of a mark does not automatically mean the item is counterfeit, especially on older or smaller pieces.
Distinct Physical Properties
Platinum possesses inherent physical characteristics that set it apart from similar-looking metals like white gold or silver. The most noticeable is its superior density, approximately 21.45 grams per cubic centimeter (g/cm³). This makes it one of the heaviest metals; for comparison, gold is about 19.32 g/cm³. Consequently, a platinum item will feel substantially heavier than an object of the same size made from gold or silver.
Platinum’s color is a natural, lustrous silvery-white that does not require plating to maintain its appearance, unlike white gold. Over time, platinum develops a soft, satiny finish known as a patina, caused by the microscopic displacement of metal rather than material loss. Platinum is also chemically stable and completely resistant to tarnishing, a process that frequently affects silver.
Safe At-Home Verification Tests
A reliable, non-destructive test involves checking the item’s magnetic properties. Platinum is non-ferromagnetic, meaning it is not attracted to a magnet. A strong neodymium magnet should be used, as common refrigerator magnets may not be powerful enough to elicit a reaction.
If the item is strongly pulled toward the magnet, it is likely a base metal or a common magnetic alloy, ruling out platinum. Note that some platinum alloys, such as those containing cobalt, can exhibit a very slight magnetic pull. A secondary observation relates to surface wear: when platinum is scratched, the metal is displaced across the surface rather than being lost, demonstrating its durability. Corrosive chemical tests, such as those involving nitric acid, should be strictly avoided in a home setting.
Professional Assessment Techniques
When an item lacks clear hallmarks or requires definitive proof, jewelers and appraisers employ specialized testing methods. One of the oldest techniques is acid testing, which involves rubbing a sample onto a testing stone to create a streak. Specific acids are applied to the streak; because platinum is highly resistant to chemical corrosion, it remains unchanged while non-platinum metals react or dissolve.
A more precise method is the specific gravity test, which mathematically determines the item’s density. The process requires weighing the object accurately in the air and then again while fully submerged in water. Comparing the resulting figure to platinum’s known specific gravity of 21.45 g/cm³ provides a reliable measure of its purity.
The most modern and accurate non-destructive technique is X-Ray Fluorescence (XRF) analysis. An XRF analyzer directs an X-ray beam onto the metal’s surface, causing the elements within the alloy to emit unique fluorescent X-ray signatures. The machine analyzes these signatures to provide a rapid, precise breakdown of the elemental composition, identifying the exact percentage of platinum and alloying metals present. This analysis offers the highest degree of certainty regarding the metal’s authenticity and fineness.