Type designer David Jonathan Ross offers up some great insight into contrast and balance in the thicks and thins of letter forms, and there relation to typography over at I LOVE TYPOGRAPHY
“Ever since I started to draw type, one of the challenges that has intrigued me the most is figuring out how letters carry their weight. Arranging thicks and thins and determining the contrast between them is crucial in assembling the systems of shapes that form a type design.
Historically, a letter’s thicks and thins emerged from the writing or drawing implement used to make it. The angle, direction, and pressure of a pen or brush can produce seemingly endless models of thick and thin in calligraphy and lettering. We sometimes carry these ideas over to typography, thinking of typographic letters in terms of imaginary mark-making tools. In type, the conventional definitions of stress and contrast are focused on the idea of stroke, telling us where a line swells to its thickest point, and how thick it actually gets.”