Technical examination of the Courtauld Gallery’s Trees by a Lake: Le Parc de Carrières-Saint-Denis, painted by André Derain in 1909, highlights the artist’s reuse of canvas following a change in his painting technique from his earlier Fauvist style to that of the 1908–14 period. The discovery of a finished underlying composition using X-radiography and evidence from concomitant technical analysis is presented in the context of Derain’s changing painterly goals during this period. Technical evidence gathered as a prelude to the recent conservation of the painting together with consultation of documentary sources raised important issues including the impact of his technique on the drying of the paint and of surface finish that influenced the approach to the subsequent treatment and display of the work in the Gallery. The consistency and range of materials and techniques used by Derain at this time were identified as a subject for future study