Outside of Argentina, Solar may best be known for his association with Borges. In 1940, he figured as a minor character in Borges's semi-fictional "Tlön, Uqbar, Orbis Tertius"; in 1944, he illustrated a limited edition (300 copies) of "Un modelo para la muerte", written by Borges and Adolfo Bioy Casares, writing together under the pseudonym B. Suárez Lynch. He and Borges had common interests in German expressionistic poetry, the works of Emanuel Swedenborg, Algernon Charles Swinburne and William Blake, and Eastern philosophy, especially Buddhism and the I Ching.