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Platinum, Silver, and Other Metals

Platinum, a precious metal, is usually mixed with other similar metals, known as the platinum group metals: iridium, palladium, ruthenium, rhodium, and osmium. The markings for platinum are based on parts per thousand and are denoted Platinum, Plat., or Pt. For instance, 900 Platinum means that 900 parts out of 1000 are pure platinum, or the item is 90% platinum and 10% other metals.

Items that contain at least 950 parts per thousand pure platinum can be marked simply "platinum".
Items that have at least 850 parts per thousand pure platinum can be marked with the amount of pure platinum and the word "platinum" or an abbreviation, for example, 950 platinum, 900 Plat., or 850 Pt.
Items that contain less than 850 parts per thousand platinum, but have a total of 950 parts per thousand of platinum group metals (of which at least 500 parts are pure platinum), should be marked with both the amount of pure platinum and the amount of the other platinum group metals in the piece. For example, the marking 600 Plat. 350 Irid. means that the item has 600 parts per thousand (60%) platinum, and 350 parts per thousand (35%) iridium, totaling 950 parts per thousand of platinum groups metals, and 50 parts per thousand (50% other metals).

Silver or sterling silver describe a product that contains 92.5% silver. Silver products sometimes may be marked 925 which means that 925 parts per thousand are pure silver. Silverplate is used to describe a layer of silver which is bonded to a base metal. The term coin silver is used for compounds that contain 90% silver. Legally, quality-marked silver also must include the tradename or trademark of the company or person that backs the jewelry.

Vermeil consists of a base of sterling silver coated or plated on the surface with gold or gold alloy of not less than 10K fineness.

Pewter items may be described and marked as such if they contain at least 90% tin.

Guidelines:

Describe jewelry as fully as possible.
Be careful with any jewelry terms that you are listing. Use the above descriptions for help, or for further assistance, contact the FTC.
List metal content. If a quality mark is only applicable to part of the product, be sure to describe this.

Source:

All That Glitters...The Jive on Jewelry, August 1998, FTC
Guides for the Jewelry, Precious Metals, and Pewter Industries, FTC