Lahner's stay in Dordogne during the war carried a lasting influence on both his art and career. The primitive forms that he had discovered in the caves began to emerge in paintings such as "Prehistoire."

Lahner's former hosts in Dordogne, the Averseng family, commissioned him to design a chapel for the town of El Affroun. This assignment provided an opportunity for Lahner to participate in the fascination with chapel construction and adornment that was then popular in France. More importantly, Lahner's exploration of stained glass and its refractive properties during this project had a profound impact on the remainder of his abstract work.

The 1950's also marked the beginning of two important relationships for the artist. In 1957, at the age of 64, Lahner married Jeanne Cazenave. And in 1959 he met an American art dealer from California named Laszlo Laky. Mr. Laky became one of the artist's closest friends.

Following his marriage, Lahner moved from his spartan studio of twenty five years on rue des Perichaux to an apartment on rue Alfred-Stevens, near the Place Pigalle.