1. Identify the host coin
Record country, denomination, date, mint, design subtype, expected composition, expected weight, diameter, edge, and normal orientation. A correct error name cannot rescue a wrong host-coin identification.
2. Describe what the metal does
3. Map it to production
Planchet errors begin before striking. Die varieties repeat on coins from one die. Strike and collar errors occur under press pressure. Edge-lettering errors may occur in a separate operation. Anything after the final production event is damage or alteration.
4. Build a disproof list
Test impact, abrasion, heat, chemical attack, corrosion, plating failure, vise pressure, jewelry use, cutting, grinding, polishing, and machine contact. The best hypothesis is the one that explains all evidence while surviving alternatives.
5. Escalate based on stakes
A low-value curiosity may only need a labeled holder and photographs. A potentially valuable wrong-planchet, mule, major brockage, famous variety, or transitional composition claim deserves specialist review or major-service certification.
Collector checklist and buying paths
The useful first question is what happened to the metal during minting. A strange appearance by itself does not prove an error or collectible premium.
- Record the host coin, approximate weight and diameter, where practical with calibrated equipment.
- Photograph both faces, the rim and edge in sharp light, with a normal coin as a scale comparison.
- Check common post-mint damage and known die varieties before selecting an error category.
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