Up to the year 2000, the 4 baht 1864 with a diameter of 45 mm was the largest flat coin produced for Thailand.
In 2000 A.D. the slightly larger Millennium coins were produced by the Singapore Mint for Thailand. They were the 65 mm Silver 200 Baht and the 55 mm Gold 2,500 Baht coins.
The 4 Baht 1864 coin was struck in gold and silver to commemorate the 60th Birthday of King Mongkut, Rama IV. The coins were used for presentation purposes and the King also permitted them to be used for decorations.
On the obverse of the 4 Baht coin there is the Crown with rays flanked with umbrellas with three branches in the background, and bordered by 32 stars, each star representing one Fuang (1/8 Baht).
The reverse has the inscription, Krung Siam enclosed within a frame and the Chinese legend Cheng Ming Tung Pao outside the frame. “Cheng Ming” is the name of King Rama IV in Chinese and “Tung Pao” means “lawful money”. There are two types; one with the double-lined frame and dots around the rim, and the other with a single-lined frame without dots.
The descriptions of the obverse and reverse are from the book “Coinage of the Rattanakosin era 1782-1982 AD”.
The gold 4 Baht coin is very rare and during the last 30 years only a few transactions have taken place. One collector had two pieces in his collection bought during the last 30 years. He later sold both sets, one by private treaty and one in an auction sale.
The 4 baht coin turns up in auctions from time to time. The price is varied, based on the quality. The prices I have seen have been from 300,000 Baht to 500,000 Baht. For a 4 Baht coin in perfect condition the price might be considerably higher. Because of the size and weight, a little more than 60 grams, this coin is considered a broad thaler.
If one would like a Thai 4 Baht coin in their collection, the alternative would be to buy a 4 Baht Tamlung, Pod Fuang or bullet coin also issued during the reign of King Mongkut, Rama 4. This very nice coin is from 1851 and originally struck for the coronation of Rama IV. The price of this bullet coin is from 50,000 Baht to 150,000 Baht depending on the quality.