Picture "Study of a Sleeping Boxer" (1956) (Unique piece)

A one-of-a-kind or unique piece is a work of art personally created by the artist. It exists only once due to the type of production (oil painting, watercolour, drawing, lost-wax sculpture etc.).

In addition to the classic unique pieces, there are also the so-called "serial unique pieces". They present a series of works with the same colour, motif and technique, manually prepared by the same artist. The serial unique pieces are rooted in "serial art", a genre of modern art that aims to create an aesthetic effect through series, repetitions, and variations of the same objects or themes or a system of constant and variable elements or principles.

The historical starting point is considered to be Claude Monet's "Les Meules" (1890/1891), where, for the first time, a series was created that went beyond a mere group of works. The other artists, who addressed to the serial art, include Claude Monet, Piet Mondrian and above all Gerhard Richter.