[1] In 1821, following negotiations by his associate Benjamin Wegner, Solly sold his collection of about 3000 works to the Prussian king; 677 of them formed a core of the Gemäldegalerie, Berlin.
During the Napoleonic Wars the firm secured immense contracts for the supply of Prussian and Polish oak timber and ship's stores from the Baltic.
Solly removed to Stockholm and then in 1813 to Berlin, overseeing the family firm's bulk purchases on the part of the European continent not covered by Napoleon's Continental System.
He sailed to England across the North Sea on board a Dutch herring boat and arrived in London twenty-four hours before the official messenger.
His great personal charm and intelligence opened the highest social circles, and as his business affairs prospered he was on good terms with ministry officials, the Prussian court, artists,[5] connoisseurs and intellectuals.
[8] Though he owned one of the finest interior views by Pieter de Hooch[9] and possibly Vermeer's Lady Standing at a Virginal (National Gallery, London),[10] both falling within the desirable contemporary category of "cabinet pictures", he was not drawn to the Seicento and Baroque Old Masters that formed the main other interest of contemporary collectors and connoisseurs, but rather to the early Byzantinising Italian paintings of the 13th and 14th centuries, which had been preserved largely in the churches and monasteries for which they had been commissioned.
[14] Following the successful sale that he had urged so long, in 1821 Solly moved to London, where he retired from shipping and dealt in works of art, which filled his house at 7, Curzon Street, Mayfair.