of Bowring Treaty was that Siamese economy was liberalized as never been before, shifting away from traditional subsistence to export-oriented economy, expanded in market volume and integrated into world economy. Rice arose to become the top export commodity, leading to rapid expansion of rice fields in Central Siam. Siam exported 60,000 tons of rice in 1857 and became one of the world's leading rice exporters in the 1860s as rice was mostly shipped to Hong Kong and Singapore. Increasing rice export put the raise on incentives of rice producers who worked more lands and produced more crop than that was simply to feed themselves. Another effect was the beginning of disparity of wealth between Central Siam and inner hinterlands when Central Siam flourished from new economies but the hinterlands, which had earlier depended on forest product trade through Central Siam, declined. Bowring Treaty also forced decriminalization of opium, which had been outlawed since 1809, in Siam. Trade agreements of Bowring Treaty and other 'unequal treaties' with Western nations also took detrimental effects on Siamese government revenues. Traditional trade tariffs was sacrificed in order to preserve the kingdom's security in regards of colonial threats. This put Siamese government in dire financial situation even in the time that Siam's economy was expanding and led to creation of fourteen even more tax farms in the reign of King Mongkut for Chinese collectors to levy. Numerous and disorganized taxes were scattered across many departments, which were under control of nobility who benefitted from their tax collection responsibilities. Largest taxes, opium tax and alcohol tax, belonged to the Bunnag-led Kalahom and Kromma Tha. Nobles responsible for tax collection treated tax farms under their control as their own properties and sought to limit their payment to government treasury at fixed rate. Government revenues were not effectively harnessed from this deranged taxation system and led to fiscal reforms by King Chulalongkorn in 1873. Currency Rattanakosin Kingdom used the silver bullet money known as Photduang () as currency until it was officially replaced with flat coins in 1904. Photduang originated in the Sukhothai period and had been in use through the Ayutthaya period. A silver bar was cut into discrete units of weight, which were melted and cast into strips that were bent to curve in the form of curled worms – hence the name Photduang meaning 'curled worm'. Photduang bullet coins were imprinted with the Chakra Seal,