Fountain pens are frequently used for calligraphy, whether by advanced professionals or beginning amateurs. The nib customizations that John performs to increase line-width variation can make your quality fountain pen into a highly suitable instrument for creating calligraphic script.
In general, the line-width variation required for creating calligraphy with a fountain pen is achieved by modifying the nib through two distinct methods. A regrind to a sharper italic point results in a pen that will give broad down-strokes and narrow cross-strokes, making this an appropriate tool for creating traditional italic style calligraphy.
Adding flex to a nib, on the other hand, allows the user to achieve line-width variation by varying the pressure used while writing - when combined with a regrind to needlepoint, this modification is well-suited for Spencerian copperplate and similar styles.