1. Jewelry Identifier
  2. Hallmarks
  3. COPPER

* base hallmark

The COPPER hallmark: meaning, purity & value

Pure copper. Antimicrobial properties; warm reddish color. Causes green skin discoloration on some wearers. Common in Southwest US Native American jewelry.

Published May 30, 2026

Quick facts

Metal
base
Common regions
international
Density
8.96 g/cm³

Stamps that mean the same thing

This purity may be struck into jewelry as any of: COPPER / Cu. The mark differs by country and era, but the metal content is identical.

What COPPER tells you

Pure copper. Antimicrobial properties; warm reddish color. Causes green skin discoloration on some wearers. Common in Southwest US Native American jewelry.

How to check it yourself

  1. Examine the stamp under a 10× loupe — genuine marks are crisp and evenly struck, not doubled or smeared.
  2. Confirm the mark reads COPPER or an equivalent such as Cu.
  3. Weigh the piece and estimate its volume — the density should land near 8.96 g/cm³ for this alloy.
  4. Photograph it in the Jewelry Identifier app to read the metal, hallmark, and any gemstones from the image.
  5. For a binding result, have an assay office or gemological lab run an XRF purity test.

* Frequently asked

FAQ

Q. Is COPPER the same as Cu?
A. Yes. COPPER, Cu all denote the same material — base. Different markets and eras stamp it differently, but the purity is identical.
Q. How do I confirm a COPPER stamp is genuine?
A. Look at the mark under 10× magnification for crisp, even strikes, cross-check the weight-to-volume ratio against the expected density (8.96 g/cm³ for this alloy), scan it with the Jewelry Identifier app, and — when it matters — have an XRF test done by an assay office or gemological lab.

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