Diagnostic Controls & Presets Samurai Gold Coinage
Diagnostic Forensic Readings
Forensic Attribution Diagnostic
Real-time metallurgical and die variety cross-examination verified against certified populations.
Technical Breakdown: Physics, Metallurgy & Die Diagnostics
Keicho: 17.8g × 0.868 = 15.45g fine gold (0.497 oz). Man'en: 3.3g × 0.574 = 1.89g fine gold (0.061 oz).
Foreign traders imported Mexican silver dollars, bought Koban at 1:5, and exported them to China/Europe at 1:15, tripling their wealth and draining Japan's gold.
Documented Benchmark Auction Records
Flawless 17.8g specimen struck under the authority of Tokugawa Ieyasu with untouched bright gold luster.
Crisp Paulownia flower crests, verified Edo Kinza mintmaster stamps on reverse.
Weighs 8.2 grams (incorrect), casts bubbles on edge, and lacks gold acid coloration.
Frequently Asked Questions
What is a Japanese Samurai Koban?
A Koban is an oval-shaped gold coin minted in Japan during the Edo period (1601–1867) under the Tokugawa Shogunate. Denominated as 1 Ryo (壱両), Koban coins were used for major commercial transactions, paying samurai stipends, and settling international trade.
What is the difference between a Koban and an Oban?
A Koban represents 1 Ryo, measuring approximately 6 to 7 cm in length and weighing 11 to 18 grams. An Oban (大判) was an enormous presentation gold plate representing 10 Ryo (over 15 cm long and weighing up to 165 grams), featuring hand-brushed black ink calligraphy (Kaki-han) by the Goto family of court assayers.
Why did the gold purity and weight of Koban coins decrease over time?
As the Tokugawa Shogunate faced escalating budgetary deficits, shoguns repeatedly debased the coinage. The Keicho Koban (1601) contained 86.8% gold and weighed 17.8g. By 1860, following the foreign exchange crisis triggered by Commodore Perry's arrival, the Man'en Koban was reduced to just 3.3 grams to stop Western traders from draining Japanese gold reserves.
What do the stamps on a genuine Koban signify?
A genuine Koban features: 1. Two Paulownia (Kiri) flower fan crests at top and bottom (the emblem of the Japanese nobility). 2. The denomination '1 Ryo' (壱両). 3. The signature mark of the Kinza (gold mint) official Mitsutsugu. 4. Era markers and assayer counterstamps on the reverse.
What is 'Color Enrichment' (Urumuki) on Japanese gold coins?
Japanese mint masters used an electrochemical depletion gilding technique. After casting and hammering the gold-silver alloy, the coins were coated in a paste of salt, copper sulfate, and sulfur, then heated. This dissolved the surface silver, leaving an ultra-pure, radiant layer of pure 24K gold on the exterior.
How can you detect a fake Japanese Koban?
Common counterfeits are made of brass, pewter, or copper dipped in gold wash. Genuine Koban feature hand-chiseled horizontal grooves (Tsuchime) cut by hammer and chisel, specific metallurgical densities matching their era, and crisp raised relief stamps without casting seams.
How much is a genuine Samurai Koban worth today?
The common Tempo Koban (1837) ranges from $1,800 to $4,500 USD depending on condition. The earlier Genbun Koban sells for $3,000 to $6,500, while the large, high-purity Keicho Koban commands $15,000 to over $35,000 USD at auction.