Thus the bakufu emitted Ansei koban, which had been made lighter to four fifths of Tenpo koban, and Ansei Nishu gin silver coins, which weighed almost half as much as a one-dollar silver coin, on June 30, 1859, in an attempt to shift to an exchange rate of 1 bu to the dollar and to modify the exchange ratio between gold and silver to 17:21, a ratio a little more favorable to gold than the international standard.
そこで幕府は、安政6年（1859年）6月1日より、天保小判の量目の4/5倍に低下させた安政小判と、量目がほぼ1ドル銀貨の半分である安政二朱銀を発行し、これにより1ドル＝一分に誘導し、かつ金銀比価を国際水準に対しやや金高に設定された17.21に是正しようと試みた。