Prior to 1945 (when Pius XII changed the form of ballot to use anonymous oaths, first carried out in 1958), the sealing wax on the complex type ballots illustrated above had the effect of making the smoke from burning the ballots either black or white, depending on whether or not damp straw was added. Until the 20th century, sealing wax customarily had beeswax mixed into its composition. The use of wax made solely from animal fat does not give as much white colored smoke, as does wax that includes beeswax. In the 1939 conclave there was some confusion over the smoke color, which was even more apparent in the 1958 conclave. The lack of sealing wax on the ballots explains the confusion over the color of the smoke in the 1958 conclave. The Siri thesis was based on the confusion over the smoke color on the first day of that conclave.