1613 a report from Paolo Sarpi on the theology of Conrad Vorstius. On his staff were Isaac Wake, and Nathaniel Brent who would later smuggle Sarpi's history of the Council of Trent out for publication in London. Carleton as a diplomat had a wide general correspondence, as well as letters from George Abbot, the Archbishop of Canterbury, concerned with English apostates and possible conversions of Catholics. He exchanged information with intelligencers such as Sarpi who had a large network, and recruited informants, such as the Neapolitan jurist Giacomo Antonio Marta. Encouraged by Walter Cope, he began also to look for works of art for Charles, Duke of York and the Earl of Salisbury; Carleton, like his predecessor in Venice Sir Henry Wotton, effectively promoted Italian aesthetics and the Grand Tour to the Stuart upper crust and looked for Venetian works of art that might be acquired by Charles I (then Duke of York) and other members of the Whitehall Group. Ambassador to the United Provinces Carleton returned home in 1615, and next year was appointed ambassador to the Netherlands. Anglo-Dutch relations were central to foreign policy and Carleton succeeded in improving these, through the Amboyna massacre, commercial disputes between the two countries, and the tendency of James I to seek alliance with Spain. The religious situation in the Netherlands had become fraught, during the Twelve Years' Truce, with the Calvinist–Arminian debate that had taken the form of a clash between Remonstrants and Counter-Remonstrants. Carleton used Matthew Slade as informant, who was a Contra-Remonstrant partisan. Maurice of Nassau supported the Contra-Remonstrants and Calvinist orthodoxy, and was vying for dominance in all seven provinces, resisted by Johan van Oldenbarnevelt who backed the Remonstrants. Carleton was himself an orthodox Genevan Calvinist, who also saw the divisive quarrel as weakening an ally. He weighed in on Maurice's side, and in line with the thinking of Abbot and the king pressed for the national Synod of Dort. A British delegation, which he helped to choose with Abbot, was led by George Carleton, a cousin. The Synod in 1618–9 resolved the theological issue, somewhat in arrears of political developments on the ground but providing the keystone to Maurice's control. Carleton at the same time continued his interests in the art trade. He exchanged marbles for paintings with Rubens, served as an intermediary for collectors like Lord Somerset, Lord Pembroke, Lord Buckingham and sent Lord Arundel paintings