Art: Onward From Olmec: Mexico: Splendors of Thirty Centuries,

"Mexico: Splendors of Thirty Centuries," which opens to the public this week at the Metropolitan Museum of Art in New York City, is the biggest show of art to leave Mexico in 50 years. There is no mystery about why it is happening. Mexico has, as the flacks say, an "image problem" in the U.S.: people think of drugs and corruption. Moreover, norteamericanos in general are abysmally ignorant of Mexican culture, its immense age, its stylistic types, its myths and its rich confluences. It makes good diplomatic sense to use one to correct the other. With the Columbian quincentennial of 1992...