Value Village ／ Clothing
This answer is a draft. It stays unpublished until legal review and source verification are complete.
"My silver has gone black" and "the gold plating has worn off" are questions asked the world over. In Japan, fineness marks (hallmarks from the Japan Mint) are common on precious-metal items, so you can usually check what you are holding before choosing how to care for it. This article explains how to read those marks and what each metal can take.
Some precious-metal items sold in Japan carry a voluntary fineness hallmark from the Japan Mint (造幣局). Examples of the stamps you may find:
| Stamp | Meaning |
|---|---|
| K18 / 750 | 75.0% gold |
| K10 / 417 | 41.7% gold |
| SV925 / 925 | 92.5% silver (sterling silver) |
| Pt900 / Pt950 | 90.0% / 95.0% platinum |
| GP / GF | Gold-plated / gold-filled (a different metal underneath) |
[Verify] Check the fineness categories and stamps on the Japan Mint's "Hallmarking of precious-metal products" page.
The blackening is sulphurisation (a reaction with sulphur in the air or in sweat), not rust (oxidation). It is a surface change only, so a silver-polishing cloth or a dedicated dip brings it back. It happens fast in hot-spring (onsen) towns.
The abrasive is coarse: plating wears off, and soft stones such as pearl, opal and turquoise get scratched. Only solid silver (SV925) should be polished this way, and then with a dedicated silver cloth rather than an abrasive one.
Pure gold (K24) hardly changes colour, but K18 and K10 contain alloying metals (silver, copper) and can discolour from sweat and cosmetics. Wiping with a soft cloth after wear is the basic habit.
Ultrasonic cleaning is not suitable for pearls, emeralds, opals or glued-in stones. Stones can loosen or crack. Use it only for hard stones such as diamond and sapphire that are securely held in prong settings.
The sulphur in hot-spring water blackens silver quickly, and chlorine (pools, bleach) damages gold alloys and plating. Taking jewellery off before bathing, swimming and housework is a habit widely shared among people living in Japan.
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https://www.mint.go.jp/operations/hallmark
https://www.kokusen.go.jp/
https://www.caa.go.jp/policies/policy/representation/household_goods/
⚠️ Editorial note: the source URLs above were identified by search. Our working environment cannot reach go.jp domains, so the contents have not been checked against the text. Verify every source before publication and record who checked it and when.
What we share here are ideas and everyday practices passed down among people living in Japan, together with general information drawn from public sources. They are not official recommendations, and they are not professional instruction. Practices vary between households and regions.
This is general information. Results vary from person to person and depend on your own conditions and surroundings.
Please decide for yourself, using your own judgement, whether any of this suits your situation. We cannot accept responsibility for any damage, loss or injury arising from following this article.
Follow the care label and the maker's instructions for any garment, shoe or bag. For expensive or sentimental items, ask a specialist cleaner or repairer.
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