Line contrast

From the Italic chapter in Learn Calligraphy.  

Line contrast is a term I invented for a concept that lies at the heart of calligraphy: the difference between thick and thin.  The alphabets in "Calligraphy Every Day" make use of this whole range: 

•  Most calligraphers like to work at near-maximum line contrast, where a broad-edged pen makes strokes that vary from very thick to very thin, depending on the direction of the pen.  Durer Caps May 2

Low line contrast is typical of pens like the Speedball D, where the thinner part of the stroke is half or two-thirds the width of the thicker part. Coopy June 12  

No line contrast characterizes a monoline, which does not vary no matter what direction the stroke.  Deco Mono May 27.  

Changing the line contrast of simple alphabets like Italic and Bookhand lets you explore dozens and dozens of styles.  Think about it while you write, and look at other people's calligraphy to analyze the line contrast.  It's all in what pen you pick.