Outside of the formal diplomatic gift exchange system, usually carried on between heads of state during or after treaty negotiations or state visits, Thailand also gave gifts to the United States on other occasions.

The Thais participated in several world expositions held in the United States in the late nineteenth and early twentieth centuries. The contents of these exhibits were given in whole or in part to the United States as direct Royal Gifts, by Royal Decree, and are now in the Smithsonian’s collections. These gifts include the entire contents of the Siam Exhibit at the 1876 Centennial Exposition, held in Philadelphia (over 900 objects), small parts of the Siam Exhibit from the New Orleans Exposition of 1884 and the World’s Columbia Exposition of 1893, and part of the Siam Exhibit displayed in the Agricultural Hall at the 1904 Louisiana Purchase Exposition, held in St. Louis (over 300 objects).

For Thailand, expositions became a new form of Royal Gift, for in most cases the Siam exhibits were given in total to the head of state of the host country, until the late 1880s when Siam established the National Museum. The exhibitor was responsible for shipping the items to the exposition and for staffing the exhibit with commissioners or guides. This exhibit/gift was not attached to any treaty negotiations, it was sent at the request of the host country expressly for the exposition. However, the traditional Royal Gift was the heart of an exposition exhibit.