He discovered the Montacute copper mine in the Mount Lofty Ranges, ten miles from Adelaide, but made no profit from it.

His collections included majolica, Hispano-Moresque ware, Luca Della Robbia and bronzes.

The collections of Elias Ashmole and John Tradescant the younger were awkwardly stored in a building on Broad Street, Oxford.

Fortnum was impressed by the efforts of Arthur John Evans to arrange and display the collections.

He offered the University of Oxford Renaissance objects, and property for the endowment of the museum, on condition that new buildings were erected to accommodate the collections.

[1] For the Council on Education Fortnum wrote the Descriptive Catalogue of the Maiolica, Hispano-Moresco, Persian, Damascus, and Rhodian Wares in the South Kensington Museum (1873), and the Descriptive Catalogue of Bronzes of European Origin (1876) in the South Kensington Museum, published in 1876.