In the early 1930s, including his time spent in Lecumberri Prison, Siqueiros produced a series of politically themed lithographs, many of which were exhibited in the United States. His lithograph "Head" was shown at the 1930 exhibition "Mexican Artists and Artists of the Mexican School" at The Delphic Studios in New York City. In 1932, he led an exhibition and conference entitled "Rectifications on Mexican Muralism" at the gallery of the Spanish Casino in Taxco, Guerrero. Shortly after, he traveled to New York, where he participated in the Weyhe Gallery's "Mexican Graphic Art" exhibition. Also in 1932, Nelbert Chouinard invited Siqueiros to Los Angeles to conduct mural workshops. It was at this time that, with a team of students, he also completed "Tropical America" in 1932, at the Italian Hall at Olvera Street in Los Angeles. Painting fresco on an outside wall – visible to passersby as well as intentional viewers – forced Siqueiros to reconsider his methodology as a muralist. He wanted the image – an Indian peon being crucified by American oppression – to be accessible from multiple angles. Instead of just constructing "an enlarged easel painting", he realized that the mural "must conform to the normal transit of a spectator." Eventually, Siqueiros would develop a mural technique that involved tracing figures onto a wall with an electric projector, photographing early wall sketches to improve perspective, and new paints, spray guns, and other tools to accommodate the surface of modern buildings and the outdoor conditions. He was unceremoniously deported from the United States for political activity the same year.