César was a key figure in the French 1960s movement known as Nouveau Réalisme. This aimed to engage directly with reality through using everyday artefacts rather than traditional art materials. In the early 1960s César made sculptures from machine-crushed pieces of metal. They were known as 'compressions'. From 1965 he worked on a series known as 'expansions', and experimented with what were for him new materials, such as glass fibre and polyester resin. This 'thumb', made for an exhibition on the theme of the hand, was based on a lifesize cast of his own thumb, scaled up using the machines traditionally employed by sculptors to enlarge their works. César made several, increasingly large versions of this work.