Graphic representation of the periodic table of chemical elements constructed as a triangle. This type of table was originated by Henry A. Wagner and Harold Simmons Booth in 1945 after an incomplete drawing by Emil V. Zmaczynski in 1937. Chemist Edward G. Mazurs classified this table as Type IIIC3-6b in his seminal work Types of Graphic Representation of the Periodic System of Chemical Elements (1957). This illustration, likely adapted by Mazurs himself, appears to be a modified version of Figure 84 on page 148 of Mazurs' 1957 publication.
Mazurs, Edward G. “Symmetrical Series Table Constructed as a Triangle.” Glass, circa 1937–1957. Edward G. Mazurs Collection of Periodic Systems Images, Box 1. Science History Institute. Philadelphia. https://digital.sciencehistory.org/works/rn3012017.