NEW YORK— Imagine if a batch of hitherto-unknown still lifes by Vermeer or views of Mont Sainte-Victoire by Cézanne were to turn up in the attic or car trunk of someone unconnected to the world of galleries, museums and auctioneers. The impact of such a discovery would be huge—and could lead to new ways of appreciating the already well-examined careers and creations of such legendary artists.

That very kind of eye-opening discovery came to light recently, not in the well-documented fields of Renaissance or Modernist painting, but in the relatively smaller and more specialized field of outsider art (a term referring to works made by untrained artists who live and work outside the cultural-social mainstream; see "Critic’s Notebook," page 121). The news that broke in late October about the emergence of 140 unknown drawings by the Mexican-born outsider Martín Ramírez (1895–1963) shook this still-evolving sector of the international art market to its foundations.

That’s because Ramírez, a poor farmer who left Mexico in 1925 for the United States, where he labored on railways and in mines and spent the last decades of his life in psychiatric hospitals in northern California, is considered one of the giants in the outsider art field. Until lately, some 300 of the self-taught artist’s pencil-on-paper and mixed-media drawings had been known to exist. However, the works that were found tucked away in Peggy Dunievitz’s garage in Auburn, California, instantly increased that number by almost 50 percent; the few experts who have seen them so far say the sometimes looser drawing style and use of abstract motifs suggest that Ramírez’s art had continued to evolve dramatically right up until his death. Considering that a single, collector-coveted Ramírez work can now fetch $100,000 or more, taken together, the newly discovered drawings could be worth millions.

In fact, Dunievitz had a sense that the stash of rolled-up paper might have had some kind of value—to someone— as meaningful art. "It looked unusual, just like the Impressionists’ paintings must have looked different to the viewers who first saw them," she says.

The former public school art teacher also knew her family could trace a link to Ramírez through her late father-in-law, Dr. Max Dunievitz. In the early 1960s, Dr. Dunievitz had served as the medical director of DeWitt State Hospital, the psychiatric facility in Auburn where Ramírez had lived for many years and where he died. Dr. Dunievitz had provided the artist with art supplies, and Ramírez had given him dozens of his drawings.

From the late 1940s through the mid-1950s, the autodidact had enjoyed a similar relationship with Tarmo Pasto, a Finnish-American psychology and art professor at nearby Sacramento State College and who regularly visited DeWitt. Pasto became interested in Ramírez’s work and organized public showings of his drawings during the artist’s lifetime. Ramírez gave works to Pasto, and it was those that the American painter Jim Nutt discovered in the 1970s and, along with his wife, the artist Gladys Nilsson and the art dealer Phyllis Kind, purchased from Pasto.

Kind presented the first exhibition of Ramírez’s rediscovered art at her Chicago gallery in 1973. (Her business is now located in New York.) Since then, appreciation of the artist’s superb draftsmanship and signature images—Mexican horsemen, madonnas, trains barreling down railway tracks and futuristic tunnels—has increased, culminating in the historic Ramírez exhibition that opened at the American Folk Art Museum (AFAM) in New York last January. That same show is now on view, through January 13, at the Milwaukee Art Museum.