Picture "Untitled" from the cycle "Castle Square in Transition" (2008)

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

In addition to the classic unique pieces, there exist 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 type 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.

In the history of arts, the starting point of this trend was the work "Les Meules" (1890/1891) by Claude Monet, in which 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.