Jewelry and gems
What the marks, grades and stones in jewelry mean.
The birthstone for each month, its colours, and where the modern list comes from.
The stamps inside rings, chains and clasps, and what each one says about the metal.
The grades on a diamond report: clarity, color, cut and carat, and what each letter and number means.
About jewelry and gems
The marks and grades that describe a piece of jewelry and its stones. Jewelry marks are the stamps on the metal that say what it is: a figure such as 925 or 14K, a plating mark, or a British hallmark. Diamond grading is the language of a diamond grading report: the clarity, color, cut and carat weight of one stone. Birthstones are the gems jewelers link with each month of birth, on a list first adopted by the American National Retail Jewelers Association in Kansas City in 1912.
Which system a mark belongs to
Figures and letters on the metal are jewelry marks: the share of pure metal, in parts per thousand (925, 585, 750) or in karats (14K, 18K). Letters and numbers that describe a diamond are grades, such as VS1 on GIA’s clarity scale or G on its D-to-Z color scale.
Karat or carat?
In the US, a karat mark on gold gives its fineness: the Federal Trade Commission’s guides let gold be marked 14K or 14 Kt., and keep the unqualified word gold for fine, 24 karat gold. A diamond’s carat is its weight, not its size, GIA explains: a metric carat is 200 milligrams, divided into 100 points. British law spells gold’s measure carat as well, and under the Hallmarking Act 1973, 18 carat gold is 750 parts per thousand.
Who sets the rules
Metal marks are set by law: in the US by the FTC’s guides and the National Gold and Silver Stamping Act, which fixes sterling at 925 parts per thousand, and in the UK by the Hallmarking Act. Diamond grades are a trade system, developed by GIA in the 1950s and used by diamond professionals, though the law reaches some of the words: the FTC’s guides call it unfair or deceptive to describe as flawless a diamond that shows any flaw to a skilled grader at 10-power magnification. The birthstone list is kept by the trade. Jewelers of America has updated its 1912 list three times, in 1952, 2002 and 2016, and George Kunz warned in 1913 against letting the momentary interest of dealers decide which stone belongs to which month.
Where the systems meet
The diamond was April’s birthstone on the 1912 list and still is, so one ring can belong to all three systems: a fineness mark on the band, and a graded diamond that is also the April birthstone.
Sources
- Guides for the Jewelry, Precious Metals, and Pewter Industries (16 CFR Part 23), 16 CFR Part 23 (1 January 2021 edition), Federal Trade Commission, published by the U.S. Government Publishing Office, § 23.4(b)(1), (c)(1); § 23.13(a)
- Falsely Stamped Gold or Silver or Goods Manufactured Therefrom (15 U.S.C. chapter 8), 15 U.S.C. 291–300, the National Gold and Silver Stamping Act (2021 edition), U.S. Government Publishing Office, §§ 296, 297
- Hallmarking Act 1973, Schedule 1, Hallmarking Act 1973 (c. 43), Sch. 1, Pt. III, legislation.gov.uk (The National Archives), Sch. 1, Pt. III, para. 2
- Hallmarking Act 1973, Schedule 2: Approved Hallmarks, Hallmarking Act 1973 (c. 43), Sch. 2, legislation.gov.uk (The National Archives), Sch. 2, Pt. I
- Diamond Quality Factors (GIA), Gemological Institute of America, The 4Cs
- Diamond Clarity (GIA 4Cs), Gemological Institute of America
- Diamond Color (GIA 4Cs), Gemological Institute of America
- Diamond Carat Weight (GIA 4Cs), Gemological Institute of America
- JA, AGTA Add Spinel as August Birthstone, National Jeweler, 2 June 2016, National Jeweler
- The Curious Lore of Precious Stones, by George Frederick Kunz, 1913, J. B. Lippincott (Project Gutenberg edition)
- April Birthstone: Diamond (GIA), Gemological Institute of America
Researched, edited and approved by Rory Hansen before publishing. Last reviewed September 29, 2026. How we research