The Yuan dynasty under Kublai Khan issued paper money backed by silver, and again banknotes supplemented by cash and copper cash. Marco Polo wrote that the money was made of mulberry bark. The standardization of paper currency allowed the Yuan court to monetize taxes and reduce carrying costs of taxes in goods as did the policy of Möngke Khan. But the forest nations of Siberia and Manchuria still paid their taxes in goods or commodities to the Mongols. Jiaochao was used only within the Yuan dynasty, and even Ilkhan Rinchindorj Gaykhatu, who was supportive of the Yuan leadership in other ways, failed to adopt the monetary experiment in his Middle East realm in 1294. As did the khanates of the Golden Horde and Chagatai Khanate, the Ilkhanate minted their own coins in gold, silver and copper. Ghazan's fiscal reforms enabled the inauguration of a unified bimetallic currency in the Ilkhanate. Chagatai Khan Kebek renewed the coinage backed by silver reserves and created a unified monetary system through the realm.