In August 1938, Wallis, Blanke, director William Dieterle, and Muni traveled to Mexico, stopping in 15 small towns, then visited the National Museum in Mexico City, where Juárez's personal papers were housed. They also managed to find a 116-year-old man who had fought with Juárez and Porfirio Diaz, and Muni questioned him about the president's mannerisms and speech patterns at length. He worked with makeup artist Perc Westmore to transform his face to resemble Juárez by changing his bone structure and skin tone, a process that took three hours each day. Despite the fact the actor closely resembled his character, studio head Jack L. Warner was unhappy with the results and complained "You mean we're paying Muni all this dough and we can't even recognize him?" However the premiere audience in Mexico City audibly gasped at first sight of Muni as Juarez, the resemblance being so remarkable.