The Othmanli sequin, ducat, Sultani, Ashraff or Sharifi, was struck originally at Cairo as the equivalent of the widely popular Venetian Ducat coin, with which it agreed in weight (3.5 grams). Nunes in 1554 mentions it under the name of Soltani as being current in Goa for 420 reis, and it is again spoken of in 1582 as being in use and of the same weight and fineness as the Venetian (Aragao, Doct 16) In 1583-8 Linschoten gives its value as 2 pardao xerafins or 600 reis.
The only Othmanli sequins found in Lanka were discovered in company with the Hormuz xerafins; all are of the sixteenth century. Coins with traceable provenance are of the following reigns.
The gold sultani from the three reigns linked above were minted in Misr which is modern Cairo in Egypt. The name Misr is used for both Egypt and Cairo. It is the most common mint found in Lanka, however the sultani shown on this website are not from circulation in Lanka, and are probably from Middle Eastern hoards.
The Calligraphy used on the coins is known as Thuluth which is a script first appears in the 10th century. The straight angular forms of Kufic were replaced in the new script by curved and oblique lines. Arabic text depends on if the character is located in beginning, middle, end or alone. The vowel additions to the characters like the dots are not necessarily written in a standard location but artistically to fill in the space available.
I find it interesting that the script changed from straight to curved around the same time as the Sinhala script developed in Lanka. Most writing changed from being chiseled on to stone to written on paper. Straight lines are simpler to chisel on stone. The Ola leaf based Paper used in lanka split by the straight text requiring a rounder font. Papyrus probably split the same way.
For the three sultani coins with images linked above there appears to be a clear improvement in the quality of the strike over the 75 year period. Does this signify a rapid improvement in their minting technology over the 16th Century. Without looking at far more of these coins I am not sure if this is a valid observation.
William Holberton(Jem Sultan) in his Guide to Ottoman Empire Numismatics, breaks down the coinage from Ottoman Empire (1300-1920) into four major periods, and these gold sultani are from Class II (1512-1648) which was from Salim I (918AH) to Mehmed IV (1058AH).
The sequin seems to have been current at one time in the Dutch period, for, according to Valentyn (c. 1726), the Moorze ducat or Moorish ducat was worth at Galle 19 fanams of 6 stuivers each or 5 guilders 14 stuivers; at Mannar 2 to 2 1/6 rix-dollars of 60 stuivers each; at Surat 4 3/16 4 1/4 or 4 5/16 rupees of 30 stuivers each ; and at Cochin 2 reals or pieces-of-eight of account. From its use in the Mocha trade it seems to have been also called the Mocha ducat. In 1782 at Batavia then so-called Turkish gold ducats were put into circulation at 1 1/2 rix-dollars the piece ; they were then stated to be entirely unknown in Ceylon.
Text edited from
I thank Nihat Ozbudun and Slobodan Sreckovic for their reading of the coins and references in reply to my post in the discussion group islamic_coins. I thank Jim Farr and Steve Album for additional information on these coins. I also thank Ahmed Badran from Egypt doing his masters in computer science at CS.CMU.edu for explaining to me the Arabic writing on the coins.