The Solot Set:

is officially the first set of stamps of Thailand. The name of this set is derived from the lowest value in the set, which is the one Solot. There are 6 values in the set. On the first day of issue, 4th August 1883 only 5 values were sold at the bangkok Post Office. There are no known examples of the postmarks from the first day of issue.

Initially only 5 values were issued. They were the one Solot, one Soi, one Sik and the one Salung. At a later date the one Fuang was received from the printer. The one Fuang value was not issued on the same day as the others. These stamps were shipped to Siam at a later date and were never officially issued for postal use.
The stamps were designed by Mr. William Ridgeway, an Englishman  who designed and engraved for Messrs. Waterlow & Sons Ltd. London. The stamps were issued in sheets of 80. Each denomination was of a different size, color and design. There were a total of 500,000 of each denomination. There are known color shade variations of all the denominations.

When Siam joined the Universal Postal Union in 1885 the foreign letter rate was set at 12 atts. At the same time the 1 Sulang stamp was revalued from 16 to 12 atts. The original issued brown ochre stamps were replace with a brown orange color, which is more clearly printed. The original 1 Sulang stamp could be exchanged and a refund of 4 atts was given.

The original brown ochre and the replacement orange brown 1 Sulang

Initially the letter rate was 2 atts and so there was little use for the one Solot stamp, being only the value of one Att. The one Solot stamps that have actually been used or affixed to covers are rarely seen. Most of the post marks on the one Solot were canceled to order. There became a huge problem when senders affixed only a one Solot stamp, being insufficient for the postal rate, so the Director of the Postal Department instructed that no further one Solot stamps were to be sold.

On the 1st July 1885 a Provisional issue was released with the denomination of one Tical. For this issue the one Solot from the first issue was overprinted in orange vermillion or red '1 Tical'. There are 5 known type settings. Type 1 (1000 issued), Type 2 (6000 issued), Type 3 (360 issued), Type 4 (300 issued), Type 5 (600 issued). Types 4 and 5 were official reprints and were never issued for use. 

On 1st May 1887 the Second Series was issued and by 1900 the use of the entire Solot Set was prohibited.

The one Soi from the first issue emerged again on the 1st August 1889 in another Provisional Issue, in which the words "one att" in Thai script were overprinted on this stamp. A total of 89,560 stamps were overprinted. Until recently only 3 type settings were known. Now, however, there are a total of 8 variations recorded. Type 1 hand stamp applied by the Post and Telecommunications Department in August 1889 using type obtained from Dr. Dan B. Bradley. There are 6 sub types, 80,000 were overprinted. The differences are in the bottom part of the right hand character being open, partialy closed or closed. Each of these is combined with the curl of the topmost character being curved upward or less curved. Type 2 hand stamp applied by the Post and Telecommunications Department obtained from Rev. Samuel J. Smith. There are 2 sub types, 9560 were overprinted. These variations are noticable by the right hand character being much more angular and the bottom most line being almost horizontal rather than sloping up.

Type 1: The Dr. Dan B Bradley Types A, B and C with the minor sub type variations


Type 2: The Rev. Samuel J. Smith Types A and B

  
There are the only 3 types recognized in the 'Scott' and 'Sakserm' catalogues. Type 1 a, b and c.

Acknowledgements: 'Chronicles of Thai Postage' Stamps by K. Pipat Choovoravech. This excelent book is a must for all serious collectors of Thai stamps.