"Untitled IX" is a drawing made primarily with silverpoint with graphite additions on gessoed paper. Higgins also utilized sanding to lighten areas of the drawing.
Metalpoint is a drawing technique that was developed in the Renaissance before the advent of the graphite pencil. Using a metal wire held in a stylus, the drawing is made on a receptive surface and traces of metal are left behind on it. Silver is traditionally used with this technique, though copper, brass, aluminum, lead, gold and other soft metals can be used. The drawing surface can be paper, board, wood, etc. and is prepared with gesso or gouache. Most metals used in metalpoint oxidize, which changes the tone and contrast of the drawing. This tarnishing/transformation continues gradually over time depending on environmental conditions.
Higgins' work is included in "Silverpoint and Metalpoint Drawing: A Complete Guide to the Medium" by Schwalb and Mazzullo, published in 2019 by Routledge.