Traits Atlas

Codebook, Minimums, Exceptions

Obsidian Patina

Summary: Dark brown-to-black patina formed by long-term surface chemistry; valued for its deep, matte to satin tonality that can push the copper into shadow.

Color: Warm blacks, umbers, rich browns; often deeper in low relief and along lettering, with thin films over open fields.

Chemistry: Frequently associated with cuprite (Cu₂O), tenorite (CuO), and copper sulfides (e.g., Cu₂S), sometimes intermixing with existing oxides.

CENT #1144 – Obsidian notable threshold — CENT #1144 – Notable obsidian (minimum)

CENT #5147 – Significant obsidian — CENT #5147 – Significant

CENT #7823 – Obsidian full — CENT #7823 – Full obsidian

Obsidian Tunings

CENT #9484 – Charcoal/graphite — CENT #9484 – Charcoal / graphite

Intensity Scale

Notable obsidian: Clearly visible brown/black toning but still localised: thin films or islands in recesses and along lettering; roughly from the minimum threshold up to ~20–30% of the face area.
Significant obsidian: Obsidian is a major visual actor with strong darkening, but not yet fully dominant; approximately ~30–70% coverage, or a smaller area with notably deep, dense shadow.
Full obsidian: Obsidian toning is the dominant surface condition, forming continuous dark regions that visually define the coin; generally > ~70% coverage with a clear dark-brown/black read at first glance.

Version 1.1 – updated to notable / significant / full scale