The Jewish framework
The important part which the Jews of London played in the importation of uncut diamonds from overseas has already been studied. The relevant documentary sources supply very little information on the second stage of the diamond trade: the link between London, the commercial centre of the trade, and the industrial centres of Amsterdam and Antwerp. The Prager letters, however, constitute a rich and unique source of information on this section of the diamond trade, which was also, to a large extent, in Jewish hands. In the eighteenth century the Dutch imported only insignificant quantities of uncut diamonds from the East, and after 1730 the diamond industry was dependent on two main sources of supply: London and Lisbon. London had a near-monopoly on Indian diamonds, 1 while Brazilian diamonds reached Amsterdam both legally — directly from Lisbon - and illegally, through London. In Portugal the diamond trade constituted a crown-monopoly and was leased to a contractor, who was usually Dutch. During most of the period covered by the Prager letters — up to 1787 - the contract was held by a certain Gildemeester, who used to distribute the stones several times a year to a limited group of customers in Amsterdam. 2 In 1787 the contract passed into the hands of the Jewish merchant Benjamin Cohen (also known as Benjamin Amersfoort), an acquaintance of the Pragers, who held it for a few years.
Formally, the possessor of the Portuguese contract had the exclusive right to distribute Brazilian diamonds in Europe. But, as the Prager letters show, side by side with this legal trade there existed a flourishing contraband trade through London. The diamonds were smuggled in the same packet-boats which carried Portuguese gold from Lisbon to Cornwall. There is, naturally, no possibility of determining either the volume of this illegal trade or its importance compared with the legal trade. But the Prager letters do show that Brazilian stones regularly reached the London market and that the 'new sort' (Brazilian diamonds) could be had there with the same ease as the 'old sort' (Indian diamonds). 3