The DuBois family in Le Locle (Jura Mountains) established the first watch factory in Switzerland in 1785. With transnational branches, such as Frankfurt and Amsterdam, it generated a worldwide trade in the following two centuries. In addition to clocks, the DuBois were also involved in colonial business. This article shows the journey of Philippe and Jean DuBois in the Transvaal in the late 19th century. They were involved in gold and salt mining in the Boer Republics. A million dollar business was created with Carl Fehr, Swiss consul in Pretoria and Johannesburg from 1894. Analysis of their networks reveals various levels of connections: members of the DuBois family in Europe; Swiss missionaries in South Africa from the Jura; the Parisian banks Berthoud and Rothschild; institutional figures like Cecil Rhodes and Roland Bonaparte; and finally, the geographical societies as a place for informal exchange. The DuBois’ South African business went fraudulently bankrupt in 1899, at the dawn of the Second Anglo-Boer War. This event provides an opportunity to understand how colonial speculation worked in practice, and shows how a family-based economic empire could be built through informal networks of transnational collaboration.