Mel Bochner, unabashed materialist? It just doesn’t sit right. Isn’t he, after all, the impresario of graph paper and measuring systems, of intangible numbers and words, of mutable materials that blow away like so many curse words in the wind? Certainly, that is one well-established side of his radical and critical split with painting-obsessed mid-century modernism. But to look at his work another way, the legendary American conceptual artist was merely paddling toward uncharted waters, expanding the definitions of materiality. In the late 1960s, Bochner had already made the iconic word portraits of his art-world friends such as Eva Hesse, Robert Smithson, and Sol LeWitt (rendering them, thesaurus-like, in a series of single-word descriptions shaped into various artful forms on paper) when he visited an exhibition of Italian frescoes at the Metropolitan Museum of Art. That 1968 show proved a revelation for Bochner, leading him to eventually pick up a piece of blue carpenter’s chalk and rub it on his own studio wall. The result was a work called “Smudge.”...