When Bencharong (Benjarong) is used to refer to porcelain it usually means a type of 18th and 19th centuries Chinese polychrome enameled 'five colored' wares, made in Jingdezhen to Thai (Siamese) specifications in the 18th and 19th centuries. The word derives from the Sanskrit panch rang meaning 'five colors', same as the Chinese wu cai.
The most popular designs on the Bencharong were Thepphanom with Norasingha, where Norasingha was a minor Buddhist deity-part man, part lion and part deer, residing in the Himaphan forest, and Thepphanom with Garuda, a mythical royal bird.
These designs were divided by a 'fire pattern' on a black background, pre-coated with green. The interior usually had an opaque green with a floral border design and an overlapping lotus on the bottom.
Originally, in the Ayutthaya period (1677-1767) it was only for the courts in Ayutthaya, Thonburi and Bangkok and was very tightly controlled. Designs were orthodox Hindu and Buddhist, bright and very heavily decorated, and the forms were frequently Indian with stupa-shaped tiered lids. The porcelain body (the paste) and the same as any other Chinese porcelains of the same periods, but the motifs are typical Thai and adapted from traditional Thai painting.
In the 19th century court control over the trade began to slip and more and more Bencharong porcelain was also ordered by the rich Sino-Thai business class that was in the process of taking over the Siamese economy. Many of the traditional court patterns were still followed but a lot of the production was really just intended for the South-east Asian market in general, with a few Thai flourishes here and there. More traditional Chinese forms such as teapots became decorated in the same style.
In the later nineteenth century small-scale efforts were made to paint Chinese blanks in Bangkok and even to manufacture porcelain there, but the quality was always low.
By the time of the Rama V period (1868-1910) the decoration had degenerated quite a bit from the very careful work (Lai Nam Thong) that one finds on earlier pieces.
Unfortunately, with the fall of the Qing dynasty and European tableware becoming fashion in Thailand the production of Bencharong was stopped in the early 20th century. Whatever production that now occurs are the same decorative items for the souvenir and decorative trade that happens with almost all ceramic products of Asia.
For further reading two important books on this topic are:
Natalie Robinson, Sino-Thai Ceramics, Bangkok, 1982, and in Thai language, but with hundreds of colored pictures, Krüang thuay Bencharong lae Lai Nam Thong, from: Khrong gaan sueb san wattana tham thai, Bangkok, 2542, ISBN 974-256-757-3.