The Iselin family archive, Basel
Finding a private archive
As a historian with an interest in questions of global history, you find an interesting article in the Historical Lexicon of Switzerland about Isaak Iselin–Roulet (1783—1841).
The transnational component of Iselin's career is appealing to you. Not only did he move to New York, where he lived for a couple of years, but he also participated in a voyage around the world and wrote a travelogue about it. It seems that he was part of an economic network between Basel and New York, and that his career developed relatively fast. Living in a comparatively early time of American global shipping commerce, Iselin seems worthy of more research.
After consulting the literature mentioned in the article and reading Iselin's book Journal of a Trading Voyage around the World, you search for recent scholarly literature about him. Not finding much of relevance, you want to know if Isaak Iselin bequeathed any papers after his death.