Franz Werfel, and on September 30 Aeneas MacKenzie began writing a first draft under associate producer Henry Blanke's supervision. According to Blanke, "Our problem from the outset in preparing this story for the screen was by no means one of glossing over facts, but rather one of cleaving to the exact line." To ensure the film was as accurate as possible, Warners head of research Herman Lissauer acquired three hundred books on the subject, and two historians were hired to help with changes to the script. Because Wallis had decided to cast Paul Muni, then one of the studio's most prestigious contract players, as Juárez, MacKenzie was instructed to make the role the most dominant in the film. His initial script was long enough for two films, and John Huston and Wolfgang Reinhardt were called in to help trim it. Abem Finkel, who had contributed to the screenplays for Marked Woman and Jezebel, worked on the dialogue but received no screen credit for his efforts. 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. On October 12, 1938, Bette Davis was offered the role of Carlota while in the midst of filming Dark Victory. Although the part was small, she welcomed the opportunity to portray an historical figure, especially one who would go mad during a dramatic confrontation with Napoléon III. She was asked to submit to makeup tests by Perc Westmore and costume fittings by Orry-Kelly but refused to do so while still working on another character. She reported to the set on December 13, two weeks after principal photography had