The gold Ichibuban of 1714 (佐渡一分判金) had a weight of 4.5 g, with 85.6% of gold and 14.2% of silver. The silver Ichibuban from 1837 to 1854 (Tenpō Ichibugin, 天保一分銀, "Old Ichibuban") weighed 8.66 g, with an alloy of 0.21% gold and 98.86% silver.
The Nibuban (二分判) was worth double the Ichibuban, and half a Koban and was also a rectangular coin.
Gold Ichibuban (一分判金)
- The Cambridge History of Japan: Early modern Japan by John Whitney Hall p.61 
- Toi Museum