Keichō Koban
慶長小判（Keichō koban） ・ aka: 慶長金
- Series
- Edo-period koban (1-ryō gold)
- Denomination
- 1 ryō
- Period
- Minting began 1601 (Keichō 6); remained the standard for c. 95 years until the Genroku recoinage of 1695
Updated: 2026-09-02
Specifications
| Item | Value | Type | Sources |
|---|---|---|---|
| Fineness & weight (museum catalog) | 84% / 18g / 1601年 | Catalog value | [1] |
| Prescribed fineness (kinza records, early) | 52.2勾位＝84.29% | Historical source | [2] |
| Prescribed fineness (later, "mimashi") | 50.7勾位＝86.8% | Historical source | [2] |
| Measured fineness (XRF, 9 specimens) | 83.6〜86.5%（平均85.4%） | Measured | [2] |
| Measured weight & size (9 specimens) | 17.70〜17.75g / 69.8〜73.5 × 38.1〜39.2mm | Measured | [2] |
| Meiji-era proclamation value | 85.69% | Historical source | [2] |
FACTThe Currency Museum permanent-exhibition catalog lists 84% fineness and 18 g weight (both rounded) with the year 1601.[1]
FACTIn the goldsmith-guild (kinza) document series, the prescribed standard fineness is 52.2 monme-kurai = 84.29%. The kinza expressed fineness in "kurai" units; per cent = (44 / kurai) × 100.[2]
FACTThe same document series records that from around the time of Gotō Shōzaburō III (installed 1641), a higher standard of 50.7 kurai = 86.8% — the "mimashi no kurai" — became the norm.[2]
MEASUREDNon-destructive analysis (electron-beam-excited X-ray) of the 9 specimens held by the Bank of Japan IMES measured gold content of 83.6–86.5% (mean 85.4%, s.d. 0.9).[2]
MEASUREDThe same 9 specimens measure 17.70–17.75 g, 69.8–73.5 mm tall and 38.1–39.2 mm wide (the catalog's 18 g is a rounded figure).[2]
FACTThe Meiji-government series (Dajōkan Proclamation No. 93, 1874) lists 85.69% from Mint analyses. Documentary standards, modern measurements, and Meiji-era proclamations are distinct value series and are deliberately not merged into one "true" figure.[2]
Visual Identification
FACTThe obverse carries gozame — horizontal striations struck into the surface. On Keichō koban these range from dense (20+ lines per cm) to coarse (5–6 per cm); koban from Genroku onward are generally coarse (roughly 4–8 per cm).[2]
FACTThe obverse bears the "Mitsutsugu" hallmark — the name of Shōzaburō Mitsutsugu I, retained by the Gotō house of the kinza as its mark under later generations as well.[2]
FACTThe kinza verification stamps on the reverse vary in position and number on Keichō koban, whereas from Genroku onward they settle at two stamps on the left.[2]
ESTIMATEA hypothesis dates individual pieces by the shift from dense to coarse gozame and from variable to fixed stamps — but the study itself states this is "only a hypothesis, without direct evidence."[2]
Varieties & Period Attribution
INTERPRETATIONNo varieties are registered as independent types. The "early (84.29%) / later (86.8%, mimashi)" split is a period attribution based on the documented change of standard, and assigning individual pieces by appearance remains hypothetical (above). Evidence is insufficient to treat these as independent varieties.[2]
Historical Context
FACTThe koban — from the Keichō koban to the Man'en koban at the era's end — held the position of standard money, always valued at one ryō.[2]
FACTThe shogunate never published koban fineness; the public of the day had no way of knowing the exact standard.[2]
FACTComparing the Keichō and Man'en koban, the weight of one ryō fell to about one-sixth and its gold content dropped by roughly 90% (museum catalog).[1]
Manufacturing
FACTProduction was carried out by the kinza under the Gotō house; the gozame striations are struck into the surface.[2]
ESTIMATEThe final "iroage" surface treatment (removing surface silver to raise gold concentration) may already have been practiced on Keichō koban, per the analysis — though period records confirm it only from Genroku onward.[2]
Authentication Cautions
INTERPRETATIONThe "Mitsutsugu" hallmark and gozame serve as research-grade diagnostics, but no single feature is known to prove authenticity on its own. Appraisal is a holistic judgment of multiple features and provenance; third-party grades assess condition and are not per se proof of historical attribution. This section is educational identification information.[2]
Known Scholarly Issues
INTERPRETATIONTwo positions coexist on the prescribed standard: an evolution from 84.3% to 86.8% around 1641, and Taya (1973), which argues 50.7 kurai (86.8%) from the outset.[2]
INTERPRETATIONTesting fineness by minting period requires separating early from late strikes, and no established method exists for doing so by appearance.[2]
INTERPRETATIONMintage and surviving population cannot be confirmed from the sources this record consults. We leave the unknown unknown rather than fill it with estimates.
Auction Records
No auction records confirmed for this exact coin type yet. Category-wide median prices are not shown as if they were prices for this type. Once confirmed, records will be listed here with auction house, sale, date, lot, grade, realized price (hammer vs. total), source URL, and review date.
References
- [1]「貨幣博物館 常設展示図録（江戸の金貨・改鋳）」（日本銀行金融研究所 貨幣博物館） — https://www.imes.boj.or.jp/cm/collection/tenjizuroku/mod/book/pageindices/index43.html（accessed: 2026-09-02）
- [2]上田道男 「江戸期小判の品位をめぐる問題と非破壊分析結果について」（金融研究 第12巻第2号（日本銀行金融研究所）、1993） — https://www.imes.boj.or.jp/research/papers/japanese/kk12-2-4.pdf（accessed: 2026-09-02）金座史料（座方算法・金位并金吹方手続書・吾職秘鑑）・明治7年太政官布告第93号・田谷[1973]等の規定品位比較（第1表）、日銀所蔵標本の実測（第3表）、電子線励起X線分析（第4表）を含む。これらの内部引用は本論文経由の孫引きとして本項に束ねる 一次史料名の言及だけでは TIER A へ昇格させない（TASK 6）。