Another year, another Cosgrove Lecture at the Centre for GeoHumanities at Royal Holloway. Our speaker this year is Siobhan Angus who has written Camera Geologica, a book tracing the interrelations of geological materiality, social-environmental history and photographic image-making. I learn that in the 19th century, 20% of global silver went into photographic production processes. Gelatin, derived from animal bones, was so important for photographic practices that slaughterhouses were kept near Kodak and other major photo studios and facilities. Platinum printing processes were used to print and archive photographs of indigenous and global south communities, and the softer, ethereal aesthetics of platinum is therefore irrevocably linked to archives of communities at the threshold of ‘disappearance’. These are the traces of what Kathryn Yusoff calls ‘geological ghosts’ in historical visual cultures. Siobhan follows the work of Azoulay in stating that photography was not born in the 19th century, it was born in 1492 upon the threshold of the colonisation (and extraction from) the Americas.