Hallmark

On the label: Hallmark · Standard and mark

What it is

An official assay-office stamp guaranteeing purity, required in the UK and some countries; the US has no hallmarking system, only the maker's trademark and the voluntary karat stamp under the National Stamping Act.

Standard and marks: The marks, tests and laws behind the words on a label: karat stamps, UV400, ANSI Z80.3, the FTC Jewelry Guides, Prop 65.

In the research

1,052 PubMed papers mention it with jewelry, allergy, eyewear or UV; the three most recent:

[Damage response mechanisms for evading neurodegeneration: mitochondrial supply driven by logistics gate disassembly] · Nihon yakurigaku zasshi. Folia pharmacologica Japonica, 2026
Clinical, neuroimaging, and genetic analyses of isolated sulfite oxidase deficiency in Chinese neonates: a retrospective case series with a narrative synthesis of previously report · Italian journal of pediatrics, 2026
Integrated Transcriptomic and Network Pharmacology Identifies IRF1, PTGS2, TNF, and IFNG as Candidate Targets of Cortex Dictamni in Atopic Dermatitis · Journal of visualized experiments : JoVE, 2026

A paper is a paper, not a verdict: titles are listed so you can read them, and a study on one fabric or one filter says little about the piece in your hand.

Other standard and marks

Karat (k, kt)Fineness (925, 750, 585)Mohs hardness scale Carat (ct)FTC Jewelry Guides Nickel-free Hypoallergenic Nickel allergy Lead in jewelry Proposition 65 ANSI Z80.3 FDA impact test (21 CFR 801.410)

Clasp & Lens describes materials from the public record and does not appraise, grade or test pieces; what a listing states is the supplier's statement. If a piece causes a rash, take it off; a reaction that spreads or blisters is a doctor's question, and sunglasses are no substitute for impact-rated eye protection where that is required.