Like many other artists, Baertling experienced resistance during his time, for a long time he was in Sweden “the constantly controversial banker who tried to paint”, despite the fact that, unlike many contemporary artists, he reached far beyond the borders of his home country during his lifetime.

From the 1940s, Baertling's painting evolved from the figurative, step by step towards the non-figurative. When the borders opened after the Second World War, Baertling, like many others, sought out the hunting grounds of the new art - France. During the first years of the 1950s, he took longer and longer leaves of absence from his banking job at Skandinaviska Banken and traveled to Paris. There, in the Mecca of art, he came into contact with the new artistic winds at the Salon des Réalités Nouvelles and sought out artists such as André Lhote, Fernand Léger, Victor Vasarely, Richard Mortensen and Auguste Herbin. The latter was crucial to his further development as an artist. Herbin introduced Baertling to the far-sighted gallerist Denise René, who immediately installed him in her 'stable' of Constructivists.

Baertling abandoned the OP art that had inspired him for some time and began to create his own style in which triangles and diagonals became the main theme. From basic geometric elements, he built up a new pictorial world of dimensions, proportions and synthetic, programmed color tones. Intense color fields enclosed in black diagonal contours create a dynamic that few other artists have managed to achieve. Baertling applied the black lines, which are slightly curved and known as sabre lines, last. During the 1960s, as is evident in the auction's “KSIA”, the angular points were moved outside the picture surface and thus he created his “open form”, in which the reflections on intersecting directions in space took on their own compositional form. Baertling preferred artificial shades that did not evoke nature and believed that black was a magical color, both light, happy and beautiful. Gunnar Berefelt describes the effect of colors on each other as follows: “Probably the most tangible and active effect in Baertling's art is the boundary contrast, when two colors get a sufficiently long and distinct boundary, they seem to alternately penetrate a little over the neighboring color's domain. It is precisely at the boundary line that the two color fields oscillate, flutter.”

“There is a Swedish artist who has made a completely original contribution to the art of our time, fully comparable to the foremost master names in modern art history - namely Olle Bærtling,” wrote Gunnar Berefeldt, professor of art history at Stockholm University, in memory of the artist in Sydsvenska Dagbladet on September 4, 1981. The exhibition, which was a collaboration with Moderna Museet in Stockholm, was planned as a tribute to Bærtling's 70th anniversary, but became a memorial exhibition due to his sudden death.