During the reign of King Chulalongkorn (King Rama V), Siam was faced with the internal modernization problems and external colonization of the western superpowers. Important changes had taken place that are reflected in the postal services then available in Siam.
Prior to August 1883 foreign postal services were carried out by forwarding agents such as A.L. Johnston & Co., Boustead & Co., Malherbe Jullien & Co., Windsor & Redlich Co., and the British, French and U.S. Consulates in Bangkok.
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The first issue stamp bore a profile portrait of King Chulalongkorn facing to the left, enclosed within an oval frame, with inscriptions of value in panels either at the top or bottom. The first issue was intended for domestic usage only as it had only Siamese characters and numerals and included the values of 1 solot (1/2 of one att), 1 att (the local printed matter single rate), 1 sio (2 atts, the local single rate for letters), 1 sik (4 atts, the inland provincial single rate), 1 fuang (8 atts) and 1 salung (16 atts).
When Siam began its postal services in august 1883 it was able to serve only areas in Bangkok with no provincial or foreign postal services. Foreign postal services were still carried out by forwarding agents and the foreign consulates in Bangkok. These services stopped in July 1885 after Siam joined the U.P.U. and started its own foreign postal services. Siam also began to expand its provincial postal services starting with Samut Prakarn in August 1885.
When Siam introduced its own foreign postal services in July 1885, the postal stationery card rate was 4 atts, the neighbouring country foreign single rate was 8 atts and the non- neighbouring foreign single rate was 12 atts. Since the one salung stamp was worth 16 atts which was more than 12 atts, it was devalued to 12 atts and used for the foreign single rate.