The first coins to carry the portrait of HM King Rama 5 were issued in 1876. These coins were minted using the latest steam powered press bought from Taylor and Challen in 1875 and carried the coat of arms, designed by Rama 5 in 1873, on reverse. This series of coins, therefore, are known as the Portrait - Coat of Arms (พระบรมรูป - ตราแผ่นดิน).
Denominations issued were 1 Fuang, 1 Salueng and 1 Baht. From 1876 to 1900 the coins did not carry dates. From 1901 onwards all coins of this series carried RS dates.
Gold 1 Fuang coins were also issued with portrait on obverse and Coat of Arms on reverse. 1 Salueng gold coin is reported to exist but are extremely rare.
Other rare coins in this series are the patterns. A copper pattern for 1 KuengTamlung (2 Baht) is up for auction at Eurseree on 28th March 2010 with a starting price of 600,000 Baht or USD 18,200.
Please refer to my previous posts Thailand: Circulating coin denominations and Thailand: Coin Dating to understand denominations and dates.
Date varieties of 1 Baht RS 121
Click to see Checklist of Portrait - Coat of Arms coins.
All coin images courtesy www.eurseree.com