This locket is likely from the 1950s to early 1960s, based on its hallmarks and construction.
1/20 GF: This stands for Gold Filled, a legal standard indicating that at least 1/20th (5%) of the item's total weight consists of gold bonded to a base metal. While gold-filled jewelry was prominent in the Victorian era, the specific "1/20" fraction format became the standardized American hallmark for gold-filled pieces in the mid-20th century.
FMB: This is the maker's mark for the Fred M. Birch company. Fred M. Birch and Samuel J. McCormick purchased control of the Briggs, Bates & Bacon jewelry manufacturing company in 1954.
Time Period: Because the FMB mark is associated with Fred M. Birch’s takeover of the company in 1954, and this style of gold-filled marking was most common through the 1950s and 60s, your locket fits perfectly into the Mid-Century era.
Manufacturer Location: FMB (Briggs, Bates & Bacon) was located in Attleboro, Massachusetts, which was once known as the "Jewelry Capital of the World"
Locket measures 3/4" diameter, chain is 18"
In very good vintage condition
Collected by Mineral and Matter