In the Spring of 1961 Lahner received critical success in a watershed exhibition at the Galerie Jeanne Castel. This exhibition was under the patronage of Lahner's old friend, Leopold Sedar Senghor, a well-known poet and the former president of Senegal.

Many of the artist's abstract works from the 1960's had the distinct geometric elements of stained glass. But the artist as always continued to press on with his personal experiments.

Colored zones of his paintings abutted one another at sharp angles, conforming to the space defined by lines. Other colored forms were blurred at the edges, as they might be in nature. Contrasting tones gave an approximation of the effects of light and shadows, but there is no specific source of illumination.

Critics writing of the Jeanne Castel exhibition found it difficult to categorize Lahner's paintings of this period. His work, they noted, reflected a synthesis of Cubistic formulae with Impressionistic color.