Thai definitive stamps

Thai definitive stamps are regular postal issues produced for postal use in Thailand, formerly known as Siam. These long-running definitive series feature royal portraits and have been produced by several different printers over time. The formal postal network was founded under King Chulalongkorn, who appointed his brother, Prince Bhanurangsi Savangwongse, in 1881 to organise and manage the system. The national service commenced operations on 4 August 1883 alongside the release of the kingdom's first definitive issue, operating from the Praisaneeyakarn post office building beside the Chao Phraya River.

The inaugural definitive release was known as the Solot Series, printed in London by Waterlow and Sons with a printing of 500,000 copies per face value. Intended to cover domestic mail services, the issue originally comprised six face values denominated in pre-decimal units: one solot, att, siao, sik, fueang, and salueng. However, the one-fueang stamp was not delivered in time for the opening of the postal service and consequently never entered circulation. Following Siam's entry into the Universal Postal Union in July 1885, the Solot Series was replaced in 1887 to meet international regulations, with subsequent definitive series adopting values denominated in att.

In terms of design, the stamps of the first definitive series depicted King Chulalongkorn shown in profile and facing to the left of the frame. A notable characteristic of this early production was the absence of any country designation or denomination inscribed in an international script. The Solot Series stands as the sole definitive group to feature the complete range of traditional pre-decimal currency units, distinguishing it from subsequent Thai definitive issues that revised denominations to comply with Universal Postal Union requirements.