Oil reinforcement is a darkroom technique used to enhance the tonal range of prints on matte or textured fibre papers. After the print has dried, it is treated with a medium made of turpentine, mastic varnish, and linseed oil, which prepares the surface for further manipulation.
Artists then apply oil paint locally to the print to deepen shadows, enrich midtones, or highlight specific areas. This method allows photographers and printmakers to add artistic control, texture, and subtle tonal adjustments, creating visually richer and more expressive images.