The critical examination of the artistic output of Kazimir Malewicz (1879—1935), intended to establish a catalogue raisonné of the work of the painter, has led the author of the present paper to emphasise some fundamental traits of his painting technique which — apart from their artisanal application — constitute an indispensable element of the painter's artistic practice. Going beyond the limits of the mere specificity of technical processes, this study reveals the aesthetic objectives in the artist's creation, present already in his Expressionist period (1910—1911), and which are far better visible in his works from the Suprematist period (1915—1918). Based on a broad repertory of technical approaches, this study of Malewicz's painting technique, and in particular on the specificity of some of his own artistic devices (lacquered watercolour, intermediary layers of varnish or the characteristic way of inscribing forms in relation to the background of a composition), shows the important aspects of an eminently expressionist conception of non-objective (abstract) forms, "pictural beings" (Malewicz 1915), which for many decades, quite falsely, had been relegated by the pretended "modernist" critics to the purgatory of "geometrical coldness". This vision had subsequently influenced abusive restorations of surfaces of numerous works by Malewicz and thus had distorted the image of Suprematism. Revealing the preliminary stages of creation of several of Malewicz's key works, such as the original Quadrilateral (called the Black Square, 1915) or the lower layers of the White Square (1918), obtained by means of technical investigation — using X-rays or digital infra-red camera — for the first time provided access to the origin of Suprematist forms. In this way one can see to what extent the Suprematist forms are the result of a painstaking, though voluntary process of purification of artistic concepts.