The apron : its traditions, history and secret significances
A Masonic study from 1914 by Frank C. Higgins, published privately in New York for an audience of Freemasons, examining the symbolism of the lambskin apron. Its diagrams are plain line drawings: a square with a circle and inscribed triangles, a bisected square with dashed construction lines, a stepped triangle lettered A to F, and a pair of squares joined at a corner. A designer might take their geometric clarity, dashed construction lines and lettered points as a model for diagrammatic instruction.
