Inseparable from the surface characteristics of the pieces is the presence of calligraphic line which appears in varying degrees in all her work. (texashistory.unt.edu)
The influence of calligraphy first became apparent in the tangled brushwork of his cityscapes of the 1930s, and Tobey went on to develop a unique style consisting of a web or network of calligraphic marks painted in white against a gray or coloured ground. (britannica.com)
Other 20th century innovators of pen drawing include the American oriental artist Mark Tobey (1890 - 1976) who was famous for his «white writing» style of calligraphic paintings; the German artist Wols (Alfred Otto Wolfgang Schulze)(1913 - 51), noted for his hair - thin graphic seismograms; and Agnes Martin (1912 - 2004), noted for her delicate hand - drawn minimalist grids. (visual-arts-cork.com)