Shakudo
On the label: Shakudo · Alloy
What it is
A Japanese copper-gold alloy that is patinated to a blue-black; used in mokume-gane and art jewelry.
Alloys: Mixtures of metals used because pure gold and silver are too soft to wear; the other metals set the color and the hardness, and sometimes the allergy question.
Wikidata: Copper alloy. Q912435 →
In the research
No PubMed papers mention this material with jewelry, allergy or eyewear; that is usual for findings and trade terms.
Other alloys
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.