Platinum is a precious metal known for its bright white color, high density, and resistance to corrosion. Determining the authenticity and purity of an item is important, whether it is jewelry or an industrial component. Testing methods range from simple, non-destructive checks suitable for consumers to detailed, laboratory-based analytical techniques.
Non-Destructive Identification Methods for Jewelry
The first step in testing a platinum piece, particularly jewelry, is to look for official markings called hallmarks. These stamps are usually found on the inside of a ring shank or on a clasp and guarantee the metal’s purity. Standard purity marks include “Pt,” “PLAT,” “950 Pt,” or “900 Plat.” The number indicates the parts per thousand of pure platinum present, with 950 being the most common high-purity standard.
Another sign is the feel of the item, which relates directly to platinum’s high density. Platinum has a density of 21.45 grams per cubic centimeter, which is higher than most other jewelry metals. A piece of platinum jewelry will feel surprisingly heavy for its size compared to a similar item made of white gold or silver.
A simple consumer test uses a common magnet. Pure platinum is paramagnetic, meaning it is not attracted to a magnet. An item that strongly sticks to a magnet is likely an alloy containing ferromagnetic metals like iron or nickel, or a non-platinum metal. However, some specialized platinum alloys, such as those made with cobalt (Pt/Co 950), can exhibit a slight magnetic response, making this test a general indicator rather than definitive proof.
Comparative Testing Against Common Lookalikes
Distinguishing platinum from white gold and palladium relies on comparing their physical and chemical properties. White gold typically receives rhodium plating, which wears off, exposing the underlying gold alloy that can have a yellowish tint. Platinum, by contrast, is naturally white and develops a soft, matte finish called a patina. This finish can easily be polished back to its original shine without re-plating.
Density remains a key differentiator. Platinum’s density (around 21.4 g/cm³) is much higher than 18K white gold (16.5 g/cm³) and palladium (12 g/cm³). This difference means a platinum ring will be almost twice as heavy as an identical palladium ring. A chemical test using nitric acid is also informative. While nitric acid reacts with common base metals and dissolves many white gold alloys, platinum is resistant and shows no reaction.
Advanced Laboratory Analysis Techniques
For accurate results, professionals rely on instrumental analysis. X-ray Fluorescence (XRF) Spectroscopy is the most common non-destructive method for precious metal analysis, providing a rapid determination of elemental composition and purity. XRF works by directing a primary X-ray beam onto the sample, causing atoms to emit secondary, or fluorescent, X-rays characteristic of the specific element present.
The most definitive, though destructive, method for high-purity analysis is the Fire Assay, also known as cupellation. This technique is the industry standard for determining the precise content of platinum group metals. It involves melting the sample with a flux and a lead collector. The cupellation process then heats the resulting lead “button,” oxidizing the lead and absorbing it into a porous cupel, leaving behind a small bead of purified precious metal for weighing.
For precise trace element analysis, particularly in refining or industrial applications, Inductively Coupled Plasma Mass Spectrometry (ICP-MS) is utilized. This method dissolves a small sample into a liquid solution, which is converted into a fine aerosol and introduced into an argon plasma at high temperatures. The plasma ionizes the elements, and a mass spectrometer separates and measures these ions based on their mass-to-charge ratio. ICP-MS can detect elements, including platinum, down to parts per billion, offering high sensitivity.