English: Resembling a Hang, or small trough for feeding animals, these long, bowed, rectangular bars called nén bac are a distinctly Vietnamese type of semi-official sycee, which was later produced outside Vietnam as well for use in the opium trade. Today most specimens come to the West via Thailand where they are called Ngern Rong. They were made from the early 1800s reportedly through World War II. Cast mainly from Spanish American 8 Reales, Indian Rupees, and French Indochina Piastres they assay consistently .991 fine. Weights generally range 370-380gm. with a likely standard of 380. Size is typically 110x31x14m except the early class which is longer and thinner. They were made by bankers (silver merchants); when presented to government officials for testing, a fee was paid and Thap (10)Lang and three other "verification stamps" were added. Bars later presented in payment of a standard 10 Lang tax were stamped on obverse (concave side) with three panels of two characters each, giving the reign title, sexagenary date, and province respectively, with a fourth Noi Te if paid at the Capital. Bars with these "royal stamps" are scarce. Treasury officials would also test scrap brought to them, and cast bars bearing the three royal stamps and the official assayer's name at the lower left side, but without the four verification stamps. Such bars are rare because the officials charged more for their services than the silver merhcants. At some point this system broke down and to meet the continuing demand for convenient, stackable ingots, silver merchants in Thailand, Hong Kong, and possibly Burma and China produced a slightly different, late version. Along with the Fu and stag-head Tael coins, these may have been used primarily in the opium trade.

   Excepting rare pieces which did not pass through official hands, the inscriptions follow a consistent pattern of four verification marks and an assayer stamp. The reverse (convex) side shows a hand-etched thâp (ten) with numerous short strokes below representing a crude Lang (Tael, Ounce) at the top of the bar. Though lacking on pieces made 1812-32, according to Thierry, three additional verification stamps were applied in relief. At the top left side (generally) is Công giáp (proper fineness), or sometimes just giáp. At the top right side (generally) is trung bín, a type of scale. The top or bottom end bears a two-character verification stamp, either Thüc khán, (true, certified) during Minh Mang and Thieu Tri, or Khán khán, (examine examine) during Tu Duc, providing a rough means of dating. Reportedly pieces with Thü thü (head) instead distinguish a piece made outside Vietnam. Finally, a fifth stamp, the Assayer's name, was added in a large panel on the lower left side. Additional stamps such as Chinese characters, symbols, a rooster, etc., often found at the bottom or middle of either side are guaranty marks of silver merchants. On the Class III bars, vertical panels of Chinese characters name the issuing bank or merchant. Some specimens have two deeply struck obverse panels closely resembling 1-Lang bars, the top being the reign title, the bottom Tinh NgânThâp Liang, a phrase properly used 1859-60 only (Thierry 1988). These were applied ca. 1900 to facilitate acceptance in the opium trade. False royal stamps are sometimes found, possibly for the same purpose, or to enhance the collector value.

   The earliest issues (Class I) were thin and flat with slightly raised obverse edges, a length around 115-117m and Thap Liang neatly etched. See Schroeder #171-172 and Thierry (1986) #115-116. Dateable published specimens are all during Minh Mang's reign (1820-41). Gold 10 Lang and thicker 40 Lang bars of this class are published. Also during Minh Mang, with specimens known for Thieu Tri, Tu Duc, and Dong Khanh, curved, slightly shorter pieces with sharply raised edges (Class II) were made. The Thap Liang is much cruder and Khán khán is added to the bottom end. This class may show guaranty stamps but no makers' names. Half-weight (170-177g) 5 Tael bars exist, though one expert believes they are not of Vietnamese origin. Class III pieces probably started around the turn of the century. Distinctly neater in appearance, the surface is smooth without craters or swellings and the angles are sharp, not rounded. The Khán khán inscription is now at the top end; the standard side inscriptions Trung bính (now a single panel) and Công giáp are much neater and consistent from piece to piece.

   Thanks to Huu Van Nguyen, former coin expert at the Saigon Museum, for much of the information used in this article.