In most countries, including the USA, any piece of jewelry sold as "antique" must be at least 100 years old. All too often the terms "antique" and "period" are used interchangeably and this is incorrect and confusing. So let’s clarify the terms.
"Period" refers to various time periods in which a particular style evolves and is popular for a certain span of time; it applies to many areas including art, architecture and jewelry. Some "period" jewelry can be antique, and there is always some degree of overlap in each "period.". Some "period" jewelry is also "antique," but most jewelry from collectible periods cannot be called "antique."
Currently the most popular and collectible jewelry "periods" include the "Victorian" period (1830s to 1900), La Belle Epoque (from 1870s till approx 1915), Art Nouveau (approx 1895-1915), Edwardian (approx 1900-1915), Art Deco (1915-into the 1930s), and Retro (1940s-early 1950s). All "Victorian" jewelry is "antique," and most of the Belle Epoque, Art Nouveau and Edwardian jewelry can also be described as "antique," but this is usually not the case with jewelry from the Art Deco and Retro periods.
While there is an overlap in the time frame for each period, each is characterized by certain design elements that have influenced the look of that period; we see it reflected in art, furniture, architecture, and so on. Certain design elements that have come to define the look of that particular "age" are also seen in jewelry. Here we see it in the very lines of the jewelry itself, as well as the use of certain gemstones, styles of cutting, and size and color of stones used. All of these elements help connoisseurs and collectors recognize a piece as being from a particular "period."
Authentic "period" pieces are highly sought after and are more costly than contemporary jewelry. This is not only because of the workmanship seen in such pieces but also because of their rarity; keep in mind most jewelry, over time, is often dramatically altered, or the stones removed and reused in a more contemporary piece, so true examples of the period are much rarer than those that are altered or reproduced along the style of a certain period.
The names of certain designers or great jewelry houses are also often associated with the finest examples of each "period" and these can add dramatically to the value/cost of authentic pieces. For example, in the Victorian period, pieces made by the Italian master, Castellani, add dramatically to desirability and value; his works were truly masterpieces. And the firm of Cartier probably stands out beyond all other jewelry houses for its Art Deco wonders, including some of the most amazing clocks – the Mystery Clocks – ever produced. And there are other great makers, designers, and jewelry houses that stand out during each period.
Reproductions, however, and authentic settings in which stones have been replaced with inferior or synthetic stones are often encountered in the marketplace. So much greater care must be taken to find a highly qualified gemologist or gemologist-appraiser to confirm any antique or period jewel is what it appears to be.