From 1964 onwards he built a highly personal body of work that is exceptionally difficult to categorize; he successfully reconciled a number of apparent contradictions such as figuration versus abstraction and the physicality of paint versus the ephemerality of the image. His work also explored the fundamentals of painting whilst also referring to his personal life and surroundings. De Keyser took the principles of the Nieuwe Visie (New Vision) and Fundamental Painting in the 1970s and used them to develop his own idiom, which was to bring him international recognition in the 1980s and '90s. The year 1980 marked the beginning of his steadily growing success, highlighted by an important one-man show in Bern and Frankfurt.