I need some help in identifying the host coin for an 1820R 960 Reis that I have. As you may know, most 960 Reis, Brazilian crown sized coins from the early 1800s, were struck over milled 8 Reales (or related coins) from Spain and the Spanish colonies in the Americas. A few were struck on virgin planchets. To my knowledge, none are known struck over hammered coins. About a year ago, I obtained an 1820R 960 Reis that appears to be struck over a hammered coin.

The coin at issue has a diameter of 43 mm (most 960s have diameters of 39 to 41 mm) and a weight of 25.5 grams (most 960s have weights close to 27 grams). The planchet is wavy and irregular and appears to me to belong to a hammered coin. The 960 was double struck, perhaps to completely cover the 43 mm, and so any details of obverse and reverse of the host coin have been obliterated. However, the original edge of the host coin is completely intact (perhaps the coin was too large to receive the "Brazilian" edge?) and has what appears to me to be Arabic script. If the host coin is an Islamic hammered coin, this 960 may be unique.

The diameter and weight of the coin seem to correspond fairly well to those of some Ottoman coins (2 kurus, 2 zolata, 2 piastres) of the late 1700s. I believe however that those coins were not hammered, and that they have plain edges. If anyone can offer some insight into what the host coin for this 960 Reis might be, I would greatly appreciate it.